Inhibitor Report for: Parathion

Organophosphorus hydrolase (OPH) is capable of hydrolyzing a wide variety of organophosphorus pesticides and chemical warfare agents. However, the hydrolytic activity of OPH against the warfare agent VX is less than 0.1% relative to its activity against parathion and paraoxon. Based on the crystal structure of OPH and the similarities it shares with acetylcholinesterase, eight OPH mutants were constructed with the goal of increasing OPH activity toward VX. The activities of crude extracts from these mutants were measured using VX, demeton-S methyl, diisopropylfluoro-phosphate, ethyl parathion, paraoxon, and EPN as substrates. One mutant (L136Y) displayed a 33% increase in the relative VX hydrolysis rate compared to wild type enzyme. The other seven mutations resulted in 55-76% decreases in the relative rates of VX hydrolysis. There was no apparent relationship between the hydrolysis rates of VX and the rates of the other organophosphorus compounds tested.

The neurotoxicities of single doses of a chemical warfare agent VX [phosphonothioic acid, methyl-S-(2-[bis(1-methylethyl)amino/ethyl) O-ethyl ester], a metabolite of the agricultural chemical parathion, paraoxon, PO (phosphonothioic acid, diethyl paranitrophenyl ester), and the known neuropathic agents DFP] phosphorofluoridic acid, bis(1-methylethyl) ester] and TOCP (phosphoric acid, tri-o-tolyl ester) were compared in the chicken. Single injections (subcutaneous, sc) of VX as high as 150 micrograms/kg (5 times the LD50, intramuscular, im) were tolerated by laying tens if atropine and 2-pralidoxime were used as antidotes before and immediately after injection. The 150 of VX for inhibition of chicken brain acetylcholinesterase was approximately 5 X 10(-10). Plasma acetylcholinesterase, but not butyrylcholinesterase, was depressed 2 h after injections of 2-20 micrograms VX/kg im without antidotes. Levels of plasma enzymes such as creatine kinase, indicative of tissue damage, were increased after exposure to both VX and PO. Injections of up to 150 micrograms/kg of VX with antidotes did not cause locomotor or histological signs of organophosphorus-induced delayed neuropathy, but single injections of 400 mg TOCP/kg did.

Alle als lnsektizide verwendbaren organischen Phosphorsaureester wie E 6O5 oder Gusathion entsprechen einem ganz bestirnmten Aufbauschema. Von besonderem lnteresse sind die systernisch wirkenden Systox-Preparate. Die neu entwickelten lnsektizide zeigen die Tendenz, die allgemeingiftigeren Phosphor-Verbindungen durch biologisch selektiv wirkende zu ersetzen https://onlinelibrary.wiley.com/doi/epdf/10.1002/ange.19570690304

Organophosphorus hydrolase (OPH) is capable of hydrolyzing a wide variety of organophosphorus pesticides and chemical warfare agents. However, the hydrolytic activity of OPH against the warfare agent VX is less than 0.1% relative to its activity against parathion and paraoxon. Based on the crystal structure of OPH and the similarities it shares with acetylcholinesterase, eight OPH mutants were constructed with the goal of increasing OPH activity toward VX. The activities of crude extracts from these mutants were measured using VX, demeton-S methyl, diisopropylfluoro-phosphate, ethyl parathion, paraoxon, and EPN as substrates. One mutant (L136Y) displayed a 33% increase in the relative VX hydrolysis rate compared to wild type enzyme. The other seven mutations resulted in 55-76% decreases in the relative rates of VX hydrolysis. There was no apparent relationship between the hydrolysis rates of VX and the rates of the other organophosphorus compounds tested.

1. Twenty-one cases out of 272 patients of acute organophosphates poisoning were diagnosed as intermediate syndrome (IMS) with a prevalence at 7.7%. The responsible OP insecticides included parathion, omethoate and some OP containing pesticide mixtures. IMS occurred mainly in severe OP poisoning patients who recovered from the acute cholinergic crisis at 7-75 h after the onset of acute poisoning. 2. Muscular weakness appeared in the following three categories of muscles: (1) neck flexors and proximal limb muscles; (2) muscles innervated by motor cranial nerves and/or (3) respiratory muscles. Blood acetylcholinesterase activity was persistently inhibited. Electroneuromyography (ENMG) with repetitive nerve stimulation (RNS) at frequencies of 20 Hz or 30 Hz in seven patients showed decrements of common muscle action potentials during the presence of myasthenia in five patients and became normal when their muscle strength recovered. 3. Mild IMS recovered within 2-7 days and had a favorable prognosis. Severe IMS patients with respiratory paralysis needed immediate endotracheal intubation and mechanical ventilation. Recovery of weakness of the respiratory muscles and proximal limb muscles took longer, the slowest being 30 days. Four of the patients died of respiratory paralysis and the fatality rate was 19%. 4. The mechanism of IMS remains to be further investigated. The RNS/ENMG changes indicate a post-synaptic block at the neuromuscular junctions. 5. In order to promote the recognition of this syndrome, we proposed to name the syndrome as Intermediate Myasthenia Syndrome (IMS).

A set of four learning and memory tests (Morris Maze I for reference memory, Morris Maze II for working memory, one-way active avoidance, and passive avoidance) were employed to address the questions whether parathion impaired cognitive functions after low, long-term exposure and could cause persistent changes in cognition. Motor activity and general behavior were investigated in a functional observational battery. Parathion was administered in rat food in low doses which caused no clinical symptoms and no or borderline brain acetylcholinesterase inhibition. Parathion doses of 0.5, 2, or 8 ppm in rat food produced the averaged uptake of 24, 100, or 400 microg/kg body weight per group per day in male rats and 36, 152, or 550 microg/kg per day in female rats in week 13. Learning tests were performed in weeks 1 to 4 and 10 to 14, as well as 30 to 34 weeks after the end of treatment, when the male and female rats were about 13 months old. Low doses of parathion given daily for 13 weeks had no cumulative or adverse effects on learning and memory, either during treatment or after the extended treatment-free period, in any of the tests. A significant improvement of learning compared to control observed in the Morris Water Maze I during the first week of treatment (males dose group 0.5 ppm) shows that parathion can improved cognitive functions in rats. Results of the study indicate that adverse effects changing learning and memory in animals may occur only at higher doses of organophosphates, at which the peripheral and brain acetylcholinesterases are inhibited to a greater extent than those in the present study.

Organophosphorus pesticides (OPs) exert acute toxicity through inhibition of acetylcholinesterase (AChE) in target tissues. Previous studies in our laboratory have demonstrated, however, that dosages of the OPs chlorpyrifos (CPF) or parathion (PS), which cause similar degrees of brain AChE inhibition in adult male rats, can produce marked differences in toxicity. While compensatory changes in postsynaptic receptors can modulate the clinical expression of AChE inhibition and lead to tolerance to these toxicants, we propose that OP-selective changes in presynaptic cholinergic processes can also regulate the ultimate consequences of AChE inhibition. The relative effects of either vehicle (peanut oil, 2 ml/kg, sc), CPF (280 mg/kg), or PS (6.6 mg/kg) on clinical signs of toxicity and AChE activity, high-affinity choline uptake (HACU), and potassium-evoked acetylcholine (ACh) release in striatum were examined for a 7-d period after exposure in adult female Sprague-Dawley rats. In vitro effects of CPF-oxon or paraoxon, the active oxidative metabolites of CPF and PS, on HACU were also examined in comparison with the prototype inhibitor hemicholinium-3 (HC-3). Similar to our previous findings in male rats, female rats treated with dosages of CPF or PS causing similar maximal degrees of AChE inhibition (82-96%) exhibited marked differences in response; that is, PS produced more extensive signs of acute toxicity (salivation, lacrimation, urination and/or defecation, i.e., SLUD signs and involuntary movements). CPF reduced striatal synaptosomal HACU at 1, 2, and 7 d after exposure, whereas PS only decreased HACU at 2 d posttreatment. While CPF-oxon was a weak inhibitor of HACU (IC50 > 200 microM), paraoxon had no effect on this process in vitro. Potassium-evoked ACh release in the presence of physostigmine (20 microM) was not affected by either OP at 1 d but was increased 2 d after either CPF or PS treatment and remained elevated at 7 d after exposure in CPF-treated rats only. ACh release in the presence of both physostigmine and the muscarinic antagonist atropine (1 microM) was decreased by both OPs as early as 1 d after exposure and remained lower at 2 d posttreatment. By 7 d, however, ACh release in response to atropine was decreased in CPF-treated animals only, suggesting that both CPF and PS affected muscarinic autoreceptor function but with somewhat different time courses. These results suggest that different OPs may selectively modify presynaptic cholinergic processes and that early, OP-selective changes in HACU/ACh synthesis may contribute to the differential toxicity noted following extensive AChE inhibition by either CPF or PS.

The majority of insecticides currently in use throughout the world belong to the class of the organophosphorus insecticides. Many of these compounds, such as the phosphorothioate insecticides, exert their mammalian toxicity only after undergoing metabolic activation by a variety of cytochrome P450 isoforms to produce their corresponding oxygen analogs (or oxons), which are potent inhibitors of the critical enzyme acetylcholinesterase. Of the many chemicals identified that can modulate cytochrome P450-dependent activities, the flavonoids represent some of the most unusual compounds in that they have been reported to both inhibit and stimulate certain activities. The present study was undertaken to determine if representative flavonoids (at in vitro concentrations of 1-100 microM) can alter the mammalian cytochrome P450-dependent biotransformation and acute toxicity of the phosphorothioate insecticide parathion. The flavonoids 5,6-benzoflavone, flavone, and quercetin had the biphasic effect of stimulating mouse hepatic microsomal parathion oxidation at a concentration of 1 microM, and inhibiting this same activity when increased to 100 microM. In contrast, 7,8-benzoflavone was only inhibitory at all concentrations examined. All the flavonoids examined except quercetin altered the ratio of activation/detoxification of parathion by mouse hepatic microsomes, but had no effect on this same ratio with human CYP1A2. These data suggest that the changes in the activation/detoxification ratio observed with mouse hepatic microsomes resulted from selective inhibition or stimulation of various cytochrome P450 isoforms rather than a flavonoid-induced alteration in the nonenzymatic rearrangement of the putative phosphooxythirane intermediate generated by cytochromes P450 from parathion. Surprisingly, however, none of the four flavonoids in the current study affected the lethality of parathion in vivo, suggesting that the flavonoid-induced alterations in cytochrome P-450-dependent metabolism of parathion documented in vitro were simply not great enough to be of any significance in vivo.

Serum paraoxonase (PON1) is an esterase that is associated with high-density lipoproteins (HDLs) in the plasma; it is involved in the detoxification of organophosphate insecticides such as parathion and chlorpyrifos. PON1 may also confer protection against coronary artery disease by destroying pro-inflammatory oxidized lipids present in oxidized low-density lipoproteins (LDLs). To study the role of PON1 in vivo, we created PON1-knockout mice by gene targeting. Compared with their wild-type littermates, PON1-deficient mice were extremely sensitive to the toxic effects of chlorpyrifos oxon, the activated form of chlorpyrifos, and were more sensitive to chlorpyrifos itself. HDLs isolated from PON1-deficient mice were unable to prevent LDL oxidation in a co-cultured cell model of the artery wall, and both HDLs and LDLs isolated from PON1-knockout mice were more susceptible to oxidation by co-cultured cells than the lipoproteins from wild-type littermates. When fed on a high-fat, high-cholesterol diet, PON1-null mice were more susceptible to atherosclerosis than their wild-type littermates.

Juvenile rats are more susceptible to the acute toxicity of the phosphorothionate insecticides parathion and chlorpyrifos than are adult rats. Developmental changes in brain acetylcholinesterase and hepatic aliesterase (carboxylesterase), cytochrome P450, and the P450-mediated metabolism of these two phosphorothionate insecticides were investigated in male Sprague-Dawley rats. Specific activities of acetylcholinesterase in cerebral cortex, but not medulla oblongata, and of liver aliesterases increased with age, indicating the presence of both more target esterases and more protective esterases, respectively, in the adult compared to the juvenile animal. Sensitivity of the brain acetylcholinesterase to inhibition by paraoxon and chlorpyrifosoxon, as measured by IC50 values, did not change significantly with age, whereas the hepatic aliesterase sensitivity to inhibition decreased with age. Progressive increases in activities of P450-mediated activation (desulfuration) (6- to 14-fold) and detoxication (dearylation) (2- to 4-fold), as well as concentrations of P450 (7-fold) and protein (2-fold), were observed between neonate and adult hepatic microsomes. Microsomal pentoxyresorufin O-dealkylase activity followed a developmental pattern similar to desulfuration and dearylation, displaying a 16-fold increase between neonates and adults. However, microsomal ethoxyresorufin O-deethylase activity increased until 21 days of age, displaying a 16-fold increase, then decreased in adulthood to a level 10-fold higher than neonates. These results indicate that target enzyme sensitivity is not responsible for age-related toxicity differences, nor is the potential for hepatic bioactivation, whereas lower levels of hepatic aliesterase-mediated protection and P450-mediated dearylation probably contribute significantly to the greater sensitivity of juveniles to phosphorothionate toxicity.

Oxidative damage was quantified in the liver of rats by measuring the levels of 8-OH-2-deoxyguanosine (8-OH-2DG) relative to 2-deoxyguanosine in DNA after treating rats for 10 days at a total dose of 1 mg/kg/day with a mixture of the 15 pesticides most commonly found in Italian foods (comprised of dithiocarbamate, benomyl, procymidone, methidathion, chlorpyrifos-ethyl, parathion-methyl, chlorpropham, parathion, vinclozolin, chlorfenvinphos, pirimiphos ethyl, thiabendazole, fenarimol, diphenylamine and chlorothalonil). We fractionated this pesticide mixture into subgroups in order to determine which molecules, if any, induced DNA oxidative damage. The administration of diphenylamine (0.09-1.4 mg/kg/day) and chlorothalonil (0.13-1 mg/kg/day) induced a dose-dependent increase in 8-OH-2DG levels in liver DNA. The other 13 pesticides of the mixture on the contrary, did not produce oxidative liver DNA damage. These results indicate that the toxicity of low doses of pesticide mixtures present in food might be further reduced by eliminating diphenylamine and chlorothalonil.

A toxicity test for organophosphates (OP) and carbamates (C) was improved with the adult ragworm Nereis diversicolor. Animals were maintained in U-shaped glass tubes of 4-mm inner diameter fixed vertically on a plastic plate and placed in glass aquaria. Each tank was covered with glass in order to reduce evaporation and heat dissipation. Temperature varied between 15 and 16 degrees C and salinity was constant (34 per thousand) during the entire length of the experiment. Experiments were performed with a fixed day length of 12 h and seawater was gently aerated. The maintenance system allowed the administration of OP and C compounds via the seawater. An acclimatization period of 48 h was not sufficient to accomodate worms to their artificial burrows; accordingly, we chose to acclimate worms for a week before beginning the exposure. Choline acetyltransferase (ChAT) activity was very low and was not significantly modified by two OP compounds: malathion and parathion-ethyl. ChAT is not a target for these pesticides and should not be used for future studies about OP and C toxicity. On the other hand, inhibitory effects on acetylcholinesterase (AChE) activity were determined at concentrations of 10(-6) M for three OP compounds-malathion, parathion-ethyl, and phosalone-and a carbamate pesticide-carbaryl. We measured only short-term effects and no cumulative effect was determined, the maximum percentage of AChE activity inhibition being between 2 (carbaryl) and 7 (OP compounds) days after exposure and then remaining stable. Mortality occured only after a period of intoxication of 14 days. N diversicolor, which can be easily maintained at the laboratory, seems to be a good candidate for future laboratory studies to test the toxicity of other pollutants.

We studied the in vitro hydrolysis of acetylsalicylic acid (ASA) to salicylic acid (SA) catalysed by microsomal preparations from liver, kidney, small intestine and stomach mucosas and blood serum of adult female and male rats. Hepatic microsomes from male rats had the highest specific activity: 42.3 +/- 6.0 nmol SA mg(-1) min(-1) (mean +/- SEM). Kidney, intestine, stomach and serum activities were 60, 30, 14 and 0.7% with regard to the liver. In contrast, gastric microsomes from female rats showed the highest specific activity: 53 +/- 22.1 nmol SA mg(-1) min(-1) (mean +/- SEM) whereas intestine, liver, kidney and serum activities were 60, 43, 40 and 1.7% with regard to the stomach mucosa. Hepatic, renal and intestinal microsomes had a pH optimum of 5-6. Male rats had Vmax and Km values of 95.5, 83.4 and 29.4 nmol SA mg(-1) min(-1) and 2.9, 1.27 and 6.4 mM, while for female rats they were 54.8, 75.8 and 59.4 nmol SA mg(-1) min(-1) and 2.6, 1.35 and 3.4 mM for hepatic, renal and intestinal microsomes, respectively. Parathion inhibited the hydrolysis of ASA with an IC50 of 1.2 x 10(-5) M for liver and kidney and 5 x 10(6) M for intestine from male rats.

1 In vitro studies with human erythrocyte acetylcholinesterase (AChE) and the mouse diaphragm model were performed to unravel the various microscopic reaction parameters that contribute to the dynamic equilibrium of AChE inhibition, ageing and reactivation. These data may help to define more precisely the indications and limitations of oxime therapy in organophosphate (OP) poisoning. 2 Diethylphosphoryl-AChE resulting from intoxications with parathion, chlorpyrifos, chlorfenvinphos, diazinon and other OPs is characterized by slow spontaneous reactivation and low propensity for ageing. This kind of phosphorylated enzyme is particularly susceptible to reactivation by oximes. 3 None of the oximes tested (pralidoxime, obidoxime, HI 6 and HLo 7) can be regarded as a universally suitable reactivator. Obidoxime turned out to be the most potent and most efficacious oxime in reactivating AChE inhibited by various classes of OP insecticides and tabun. Obidoxime, however, was inferior to HI 6 against soman, sarin, cyclosarin and VX. Pralidoxime was generally less potent. 4 The kinetic data of reactivation established for diethylphosphoryl-AChE of human red cells indicate that the usually recommended dosage to attain a plasma concentration of 4 micrograms/ml does not permit exploitation of the full therapeutic potential of the oximes, in particular of pralidoxime. However, in suicidal mega-dose poisoning, oximes, even at optimal plasma concentrations, may be unable to cope with the fast re-inhibition of reactivated AChE in the first days following intoxication. 5 It is suggested that oximes be administered by continuous infusion following an initial bolus dose as long as reactivation can be expected and until permanent clinical improvement is achieved.

Cholinesterase (ChE) in brain and muscle was quickly inhibited during a 48-hr in vivo exposure to chlorpyrifos (0.1 ppm), parathion (0.15 ppm), and methyl parathion (8 ppm) in mosquitofish (Gambusia affinis). ChE remained inhibited during a 96-hr nonexposure period. Brain ChE reached peak inhibition by 12 hr after exposure to parathion and chlorpyrifos and by 4 hr after exposure to methyl parathion. All insecticides caused greater than 70% ChE inhibition by 4 hr in muscle. There was no recovery of ChE after 4 days of nonexposure in either brain or muscle. Hepatic aliesterases (AliE) were quickly and greatly inhibited (> 70% by 4 hr) after exposure to parathion and chlorpyrifos but not after exposure to methyl parathion. Exposure to methyl parathion required 24-36 hr to inhibit hepatic AliE to the same level as that following parathion and chlorpyrifos exposures at 4 hr. Exposure to all insecticides eventually resulted in greater than 80% inhibition of AliE. None of the test groups treated with insecticides showed any signs of significant recovery of AliE during the 4 days of nonexposure. Nonprotein sulfhydryl (NPSH) concentrations were lower than controls after 24 hr of exposure and 96 hr after recovery for all compounds. Exposure to methyl parathion lowered NPSH concentrations greater than the other compounds. Hepatic AliE appear capable of affording some protection of ChE from inhibition following parathion or chlorpyrifos exposures, but considerably less protection against methyl parathion.

In rats, the phosphorothionate insecticide parathion exhibits greater toxicity than chlorpyrifos, while in catfish the toxicities are reversed. The in vitro inhibition of brain acetylcholinesterase (AChE) by the active metabolites of the insecticides and the rates at which these inhibitor-enzyme complexes undergo reactivation/ aging were investigated in both species. Rat AChE was more sensitive to inhibition than catfish AChE as demonstrated by greater bimolecular rate constants (ki) in rats than in catfish. In both species, chlorpyrifos-oxon yielded higher ki's than paraoxon. The higher association constant (KA) of chlorpyrifos-oxon than paraoxon in both species and the lack of significant differences in the phosphorylation constants (kp) suggest that association of the inhibitor with AChE is the principal factor in the different potencies between these two inhibitors. In catfish, the ki of chlorpyrifos-oxon was 22-fold greater than that of paraoxon, while in rats it was 9-fold greater, suggesting that target site sensitivity is an important factor in the higher toxicity of chlorpyrifos to catfish but not in the higher toxicity of parathion to rats. No spontaneous reactivation of phosphorylated catfish AChE occurred and there were no differences in the first oder aging constants (ka) between compounds. For phosphorylated rat AChE, there were no differences in the first order reactivation constants (kr) but the ka for chlorpyrifos-oxon was significantly greater than that for paraoxon. This difference suggests that the steric positioning of the diethyl phosphate in the esteratic site is not the same between the two compounds, leading to differences in aging.

Paraoxon (O,O-diethyl O-p-nitrophenyl phosphate) is the neurotoxic metabolite of the insecticide parathion (O,O-diethyl O-p-nitrophenyl phosphorothioate). The effects of organophosphorus compounds on peripheral synapses have been attributed to inhibition of cholinesterase and to direct actions on muscarinic and nicotinic receptors, but less is known about the actions of organophosphorus compounds, including paraoxon, in the central nervous system. We investigated initially the effects of paraoxon on spontaneous transmitter release by recording miniature postsynaptic currents (MPSCs) from cultured rat hippocampal neurons using the whole-cell mode of the patch-clamp technique. Paraoxon (0.3 microM) in the presence of tetrodotoxin (0.3 microM) and atropine (1 microM) caused a significant increase in the frequency of gamma-aminobutyric acid- and glutamate-mediated MPSCs, but did not change the peak amplitudes or decay-time constants of these MPSCs. In contrast, application of nicotinic agonists or antagonists did not change the MPSC frequency. The presynaptic effect of paraoxon shown here was not mediated by actions on muscarinic or nicotinic receptors, or by elevated acetylcholine levels secondary to inhibition of cholinesterase. In addition, agonists were applied to assess the postsynaptic effects of paraoxon on excitatory and inhibitory amino acid receptors. Paraoxon (30 microM-1 mM) blocked the ion channels of glycine, gamma-aminobutyric acidA, N-methyl-D-aspartic acid and nicotinic acetylcholine receptors, but not the ion channels of kalnate- and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors. The combined effects of paraoxon on spontaneous transmitter release and on the functions of several ligand-gated receptors may constitute mechanisms relevant to the neurotoxicity of paraoxon.

The acute toxicity of chlorpyrifos, methylchlorpyrifos, parathion and methylparathion to three age classes of Artemia salina was determined. In general, A. salina 24-h old was less sensitive to these organophosphorous insecticides (OPI) than A. salina 48-h old and A. salina 48-h old was significantly more tolerant than A. salina 72-h old, in contrast, chlorpyrifos was equally toxic to A. salina 48- and 72-h old. There were some differences among the three age classes of A. salina in the relative order of toxicity of OPI tested. The rank order of toxicity to A. salina 48-h old was methylparathion < parathion < methyl-chlorpyrifos < chlorpyrifos, while to A. salina 24- and 72-h old it was methylparathion = parathion < methyl-chlorpyrifos < chlorpyrifos. The protective effect of the cholinergic antagonists atropine, hexamethonium, pirenzepine and 11-(2-((diethyl-amino)methyl)-1-piperidinylacetyl)-5, 11-dihydro-6H-pyrido(2,3-b)-(1,4)-benzodiazepine-6-one (AF-DX 116) and a cholinesterase-reactivating oxime 2-pyridine aldoxime methochloride (2-PAM) on the mortality due to four selected OPI in Artemia salina 24-h old was investigated. The lethal action of OPI tested was completely prevented by pretreatment of Artemia salina 24-h old with 2-PAM (10(-5) M) and atropine (10(-4 )M). However no concentration of hexamethonium, pirenzepine or AF-DX 116 protected 100% of the animals poisoned by LC84 of the OPI selected, maximum protection obtained was 71 to 88%. In contrast, the maximum inhibition of mortality obtained with AF-DX 116 pretreatment was about 55% because this compound was used at concentrations which were non toxic to control Artemia salina. Atropine, hexamethonium, pirenzepine, AF-DX 116 and 2-PAM afforded 50 % protection (IC50) of Artemia salina against mortality by LC84 of the OPI selected at concentrations in the range of 6.62x10(-7)-1.6x10(-6) M, 2. 38x10(-4)-2.05x10(-3)M, 8.91x10(-7)-1.24x10(-6) M, 9.66x10(-8)-1. 34x10(-7 )M, and 1.95x10(-8)-2.73x10(-8 )M, respectively. Pretreatment of atropine plus 2-PAM to determine whether this combination afforded greater inhibition of the lethality induced by four OPI tested than pretreatment with either atropine or 2-PAM alone was investigated. Atropine (10(-5) M) in combination with 2-PAM (10(-7 )M) inhibited completely the acute toxicity of all OPI tested, while the pretreatment with atropine (10(-6) M) plus 2-PAM at the same concentration gave a inhibition of mortality (about 62%) significantly greater than each antagonist alone (about 14 and 46%, respectively).

The inhibition and aging of acetylcholinesterase (AChE) in fingerling channel catfish (lctalurus punctatus) brain tissue was studied after single in vivo exposures to high levels of chlorpyrifos (0.25 mg/L), chlorpyrifos-oxon (7 micrograms/L), parathion (2.5 mg/L), or paraoxon (30 micrograms/L). Exposure to both parent compounds produced identical initial inhibition (95%), but in the later sampling times there was significantly more inhibited AChE in the chlorpyrifos-treated fish than in the parathion-treated fish (47% and 28%, respectively, on d 16). There were higher levels of aged AChE following chlorpyrifos exposure than following parathion exposure, but differences were not significant. Exposure to both oxons produced initial inhibition greater than 90%, and patterns of recovery and aging were statistically similar between both compounds; no significant inhibition was observed after d 11. The similar patterns of inhibition, recovery, and aging between the two oxon treatments, which have similar lipophilicities, suggest that the greater amount of AChE inhibition and aging observed in the chlorpyrifos-treated fish compared with the parathion-treated fish probably results from the higher lipophilicity of chlorpyrifos than of parathion. Overall, the prolonged brain AChE inhibition exhibited in catfish exposed to phosphorothionates is not the result of aging of the inhibited enzyme but is the result of either a slow rate or a lack of spontaneous reactivation.

Annealed murine erythrocytes were employed as a carrier model to antagonize the toxic effects of organophosphorus agents. These resealed cells containing a recombinant phosphotriesterase provided striking protection against the lethal effect of paraoxon, an active metabolite of an agricultural pesticide, parathion. Phosphotriesterase hydrolyzes paraoxon to the less-toxic 4-nitrophenol and diethylphosphate. This enzyme was encapsulated into carrier erythrocytes by hypotonic dialysis with subsequent resealing and annealing. These carrier cells were administered to mice either alone or in combination with pralidoxime (2-PAM) and/or atropine. The recipient animals were subsequently challenged with paraoxon and a marked protection was noted. Protection of free enzyme and encapsulated enzyme was compared and the encapsulated enzyme was found to persist longer and possess much greater efficacy. Less serum cholinesterase inhibition also was observed with this enhanced protection. These results indicate that the erythrocyte carrier alone is quite effective in the antagonism of organophosphorus intoxication. Moreover, when these carrier cells were administered in combination with 2-PAM and/or atropine, a marked synergism was observed.

Lymphocytes obtained from 5 healthy donors were incubated with a mixture of 15 pesticides commonly found in foods of central Italy (dithiocarbamates (20.7%), benomyl (19.6%), thiabendazole (14.9%), diphenylamine (14.4%), chlorthalonil (13.1%), procymidone (8.0%), methidathion (2.3%), chlorpyrifos-ethyl (2%), fenarimol (1.9%), parathion-methyl (1%), chlorpropham, parathion, vinchlozolin, chlorfenvinphos and pirimiphos-ethyl (< 1%)). The percent of each pesticide in the mixture was proportional to its average concentration in foods. Incubated with the lymphocytes at a concentration of 1-20 micrograms/ml the pesticide mixture did not induce significant variations in the number of hypodiploid, hyperdiploid and polyploid cells or in the number of chromosome and chromatid aberrations. On the contrary, we observed a dose-dependent increase in the number of nonsynchronous centromeric separations which reached the level of 37.9% at 20 micrograms/ml of pesticide mixture in the incubation medium. This effect was not observed when benomyl was excluded from the mixture. These data show that the removal of benomyl could decrease the toxicity of pesticide residues present in human food.

The level of 8-OH-2-deoxyguanosine in rat liver DNA was measured as an index of oxidative damage after treating rats for 10 days at a dose ranging from 0.75 to 10 mg/kg with a mixture of 15 pesticides (dithiocarbamate, benomyl, thiabendazole, diphenylamine, chlorthalonil, procimidone, methidathion, chlorpyrifos-ethyl, fenarimol, parathion-methyl, chlorpropham, parathion, vinclozolin, chlorfenvinphos, pirimiphos-ethyl) commonly found in foods of central Italy. At the doses of 0.75 and 1 mg/kg DNA levels of 8-OH-2-deoxyguanosine were significantly increased relative to controls, whereas at higher doses (2.5, 5, 10 mg/kg) the levels returned to control values. The administration of the pesticide mixture dose dependently reduced benzo(a)pyrene hydroxylase, N-demethylase activities, glutathione peroxidase, glutathione reductase, glutathione-S-transferase and thiol transferase activities in the liver. The results show that the pesticide mixture induced free radical DNA damage at low doses. However, at higher doses it produced a depression of cellular metabolism, inhibiting a further expression of oxidative damage.

Inhibitory (ki), spontaneous (k0), and oxime-mediated reactivation (k(oxime)) reaction kinetics for the four stereoisomers of isomalathion (SPRC,SPSC,RPRC, and RPSC) were determined against rat brain acetylcholinesterase (AChE). (SPRC)-Isomalathion was the most potent anticholinesterase agent and RPSC-isomalathion the least potent with racemic material approximately midway in activity. Following inhibition of rat brain AChE by (SPRC)- or (SPSC)-isomalathion, k0 and k(oxime) values were obtained that were comparable to (SP)-isoparathion methyl, indicating that the same mechanism of inhibition was shared, namely, formation of an O,S-dimethyl phosphorothiolated enzyme. Conversely, no appreciable reactivation occurred with or without oxime following inhibition of rat brain AChE by (RPSC)- or (RPRC)-isomalathion. This observation was not consistent with (RP)-isoparathion methyl, and a switch in inhibition mechanism to the loss of the thiomethyl moiety is suggested. The nonreactivation of rat brain AChE following inhibition by the (RP)-isomalathion stereoisomers is postulated to result from a mechanism involving either a beta-elimination of diethyl fumarate or displacement of the thiosuccinate moiety from the phosphate moiety.

The biomolecular reaction constants (ki), dissociation constants (Kd), and phosphorylation constants (kp) were determined for the enantiomers of malaoxon against rat brain acetylcholinesterase, and for the stereoisomers of isomalathion against rat brain acetylcholinesterase and electric eel acetylcholinesterase. (R)-Malaoxon was an 8.6-fold more potent anti-cholinesterase than (S)-malaoxon. Isomalathion stereoisomers with the R configuration at carbon were 3-13-fold stronger inhibitors than those with the S configuration. The isomalathion stereoisomers with the R configuration at phosphorus were 4.3-8.8-fold stronger inhibitors of rat brain acetylcholinesterase, yet 3.4-5.8-fold weaker inhibitors of electric eel acetylcholinesterase, than the isomalathion stereoisomers with the S configuration at phosphorus. The rat brain acetylcholinesterase spontaneous (k0 = approximately 13.0 x 10(-3) min-1) and oxime-mediated (koxime) = 51.0 x 10(-3) min-1) reactivation rate constants following inhibition by isomalathion stereoisomers with the R configuration at phosphorus were comparable to spontaneous (11.3 x 10(-3) min-1) and oxime-mediated (50.2 x 10(-3) min-1) reactivation rates obtained for (S)-isoparathion methyl. These data support a common phosphorylation mechanism, namely, the displacement of the thiosuccinyl moiety from isomalathion stereoisomers with the R configuration at phosphorus, and displacement of the p-nitrophenoxy ligand from (S)-isoparathion methyl to form the same O,S-dimethyl phosphorothiolated enzyme. Rat brain acetylcholinesterase inhibited by the isomalathion stereoisomers with the S configuration at phosphorus were refractory to reactivation, suggesting an alternate mechanism of inhibition, i.e., the loss of the methylthio ligand. Several mechanisms are proposed to account for the subsequent nonreactivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Rats were administered high sublethal intraperitoneal dosages of the phosphorothionate insecticides parathion, methyl parathion, and chlorpyrifos, and their oxons. Acetylcholinesterase activities in cerebral cortex and medulla oblongata and aliesterase activities in liver and plasma were monitored at 2 hr and 1, 2, and 4 days after exposure. The maximal inhibition of brain acetylcholinesterase activity was not immediate with parathion and chlorpyrifos, reflecting the time required for bioactivation of the phosphorothionates as well as the effectiveness of the aliesterases to inactivate much of the hepatically generated oxons. In contrast, brain acetylcholinesterase activities were more quickly inhibited following administration of paraoxon and chlorpyrifos-oxon, which do not require bioactivation. Brain acetylcholinesterase was also rapidly inhibited following administration of methyl parathion and methyl paraoxon, reflecting the low sensitivity of the aliesterases to methyl paraoxon. Aliesterases were inhibited to a greater extent than acetylcholinesterase at each sampling time with parathion and chlorpyrifos and their oxons, whereas the reverse was true with methyl parathion and methyl paraoxon. All of the above patterns correlate with the in vitro sensitivities of acetylcholinesterase and aliesterases to the oxons. The very prolonged inhibition of esterase activities following chlorpyrifos treatment probably results from its substantially greater lipophilicity compared to the other compounds, which would allow it to be stored and released for gradual bioactivation. The data reported indicate that the disposition and effects of different phosphorothionate insecticides will be influenced by the sensitivities of target and nontarget esterases for their oxons and by their lipophilicity, and that predictions of in vivo responses can be made from in vitro data.

OBJECTIVES To estimate the frequency of the intermediate syndrome in organophosphorus-poisoned patients, and examine its relationship to cholinesterase inhibition and electromyographic findings. Muscle biopsies were available in some patients. DESIGN: A 3-yr prospective study. SETTING: University teaching hospital intensive care unit. PATIENTS: Consecutive patients with acute organophosphorus poisoning (n = 19). MEASUREMENTS AND MAIN RESULTS: We determined the frequency of the intermediate syndrome in poisonings with various organophosphates, duration of (acetyl) cholinesterase inhibition and metabolite excretion, evolution of alterations on repetitive nerve stimulation, type and frequency of muscle lesions. A total of eight of 19 patients developed an intermediate syndrome. In some patients, short relapses of muscarinic symptoms superimposed on the intermediate syndrome. Agents such as methylparathion, fenthion, and dimethoate carry a high risk, but we also noted a prolonged intermediate syndrome in an ethyl-parathion-poisoned patient. Prolonged and severe cholinesterase inhibition occurred during the intermediate syndrome in all patients, and metabolite excretion was prolonged. As the intermediate syndrome evolved, repetitive nerve stimulation initially demonstrated decrement, then increment, and finally, normal responses. Necrotic fibers were noted in muscle biopsies, but these fibers were too sparse to explain severe muscle weakness and were similar in patients with and without the intermediate syndrome. No patients developed delayed neuropathy. CONCLUSIONS: The intermediate syndrome is not rare. Although it is more likely to occur with some organophosphates, it is not confined to a few distinct compounds. This syndrome coincides with prolonged cholinesterase inhibition, and is not due to muscle fiber necrosis. When viewed together, the clinical and electromyographic features are best explained by combined pre- and postsynaptic dysfunction of neuromuscular transmission. The intermediate syndrome is not related to an incipient delayed neuropathy.

To determine the toxicological effects of complex mixtures of pesticides, we obtained data on 100 pesticide residues in common foods of central Italy. Fifteen pesticides were more regularly detected at higher levels (dithiocarbamates, benomyl/carbendazim, thiabendazole, diphenylamine, chlorthalonil, procymidone, fenarimol, chlorpropham, vinchlozolin, methidathion, chlorpyriphos-ethyl, parathion-methyl, parathion, chlorfenviphos, pirimiphos-ethyl). Using itemized data on daily food consumption in Italy, we calculated that the average exposure for an adult subject was 716 micrograms/day, ranging from 148 micrograms of dithiocarbamates to 1 microgram of pirimiphos-ethyl. We made a mixture of these 15 pesticides at concentrations proportional to the ratio determined in foods and tested it with the Salmonella-microsome assay, with and without metabolic activation with PCB-induced rat liver S9. No mutagenic activity was observed at concentrations up to 500 micrograms/plate. We also tested the same mixture at concentrations ranging from 0.1 to 20 micrograms/ml on human lymphocytes in vitro, and observed a slight but statistically significant increase in sister-chromatid exchanges at 1 microgram/ml. We also administered the mixture in corn oil by gavage to Wistar rats at doses of 1, 10, and 100 micrograms/kg. After 24 hr the ratio between bone marrow polychromatic and normochromatic lymphocytes (a sign of cellular toxicity) was decreased by the exposure, but we did not observe a significant increase in the frequency of micronuclei. We conclude that the pesticide mixture did not have appreciable genotoxic activity in the assays used.

In 40 experiments on 20 pigs three different organophosphorus insecticides (OPs), parathion (n = 6), phoxim (n = 7) and phosmet (n = 7), were administered both intravenously (i.v.) and dermally (d.) as 'pour-ons' in a crossover design in order to determine the dermal bioavailability of the OPs. As percutaneous absorption of drugs may be affected by the vehicle used, three chemically different vehicles--DMSO, 1-octanol and macrogol 400-were used for the dermal administration of each of the OPs. The pharmacokinetic parameters measured showed that 15-30% of dermally applied parathion is absorbed when administered in DMSO or octanol, but only 4-5% when administered in macrogol. Absorption was fastest with DMSO and slowest with macrogol. For the two ectoparasiticides, phoxim and phosmet, only between 0.5 and 3% of the dermal dose was absorbed with little difference in the absorption rate between the three vehicles. On the basis of the very limited dermal bioavailability for these two OPs it seems doubtful whether sufficient concentrations can reach the ectoparasites through the systemic route.

The effect of ad libitum dietary exposure (as occurs in the field) to parathion for 14 d was investigated on the muscarinic acetylcholine receptor (mAChR) in brains and submaxillary glands of adults of a field species, the white-footed mouse Peromyscus leucopus. Immunoprecipitation using subtype selective antibodies revealed that the relative ratios of the m1-m5 mAChR subtypes in Peromyscus brain were similar to those in rat brain. There was little variability in acetylcholinesterase (AChE) activity in control mice brains but large variability in 39 exposed mice, resulting from differences in food ingestion and parathion metabolism. Accordingly, data on radioligand binding to mAChRs in each mouse brain were correlated with brain AChE activity in the same mouse, and AChE inhibition served as a biomarker of exposure reflecting in situ paraoxon concentrations. Exposure to parathion for 14 d reduced maximal binding (Bmax) of [3H]quinuclidinyl benzilate ([3H]QNB), [3H]-N-methylscopolamine ([3H]NMS), and [3H]-4-diphenylacetoxy-N-methylpiperidine methiodide ([3H]-4-DAMP) by up to approximately 58% without affecting receptor affinities for these ligands. Maximal reduction in Bmax of [3H]QNB and [3H]-4-DAMP binding occurred in mice with highest AChE inhibition, while equivalent maximal reduction in Bmax of [3H]NMS occurred in mice with only approximately 10% AChE inhibition, without further change at higher parathion doses. This is believed to be due to the hydrophilicity of [3H]NMS, which limits its accessibility to internalized desensitized receptors. In submaxillary glands (mAChRs are predominantly m3 subtype), there were significant dose-dependent reductions in [3H]QNB binding and m3 mRNA levels in exposed mice, revealed by Northern blot analyses. The reduction in m3 receptors is suggested to result mostly from reduced synthesis at the transcription level, rather than from translational or posttranslational events. The data suggest that down-regulation of mAChRs occurs after dietary exposure for 14 d to sublethal concentrations of parathion in a field rodent species, and that significant though incomplete recovery in AChE and mAChRs occurs in 7 d following termination of exposure.

A number of lines of evidence suggest that serum paraoxonase is protective against poisoning by organophosphorus substrates of this enzyme. Birds that have very low levels of paraoxon hydrolyzing activity in their sera are very susceptible to parathion poisoning. Rabbits, which have a sevenfold higher enzyme level compared with rats, have a fourfold higher resistance to paraoxon poisoning than rats. Rabbit paraoxonase hydrolyzes chlorpyrifos-oxon with a much higher turnover number than does rat paraoxonase, resulting in a very high resistance of rabbits to chlorpyrifos toxicity. Direct tests of paraoxonase protection have been carried out by injecting purified rabbit enzyme into rats. The protection achieved was higher for chlorpyrifos-oxon than for paraoxon, probably due to the high hydrolytic activity of the rabbit enzyme for chlorpyrifos-oxon. In humans, a substrate-dependent polymorphism of serum paraoxonase is observed, where one isoform of paraoxonase has a high turnover number for paraoxon and the other a low turnover number. Both isoforms appear to hydrolyze chlorpyrifos-oxon and phenylacetate at the same rate. Cloning and sequencing of the human paraoxonase cDNAs has elucidated the molecular basis of the polymorphism. Arginine at position 192 determines high paraoxonase activity, and glutamine at this position, low paraoxonase activity. In addition to the polymorphism, a 13-fold variation in serum enzyme levels within a given genetic class is seen. The experiments reported here demonstrate that rabbit paraoxonase injected into mice provides protection against the parent insecticide chlorpyrifos as well as the toxic oxon. These results suggest that serum paraoxonase status may serve as a biomarker for insecticide susceptibility in humans.

Some compounds that inhibit acetylcholinesterase (AChE) activity compete directly with quinuclidinyl benzilate (QNB) binding, a muscarinic antagonist which binds to all subtypes equally, and with cis-methyldioxolane (CD), an agonist that binds with high affinity to the M2 subtype of muscarinic receptors. The relationship between inhibition of AChE activity and the capability to affect muscarinic receptors directly has not been systematically explored. The interaction of eight organophosphates with muscarinic receptors was compared to their ability to inhibit AChE activity in vitro in tissue homogenates from rat hippocampus and frontal cortex, two cholinergically enriched areas of the brain. Of the compounds tested only echothiophate competed for [3H]QNB binding and only at concentrations greater than 100 microM. The anticholinesterase compounds were also tested for their ability to compete with a muscarinic receptor agonist, [3H]CD, which binds with high affinity (approximate KD = 3.5 nM) to 10 and 3% of the muscarinic receptors in the frontal cortex and hippocampus, respectively. The anticholinesterase compounds inhibited high-affinity [3H]CD binding up to 80% and the effects were similar in both tissues. Echothiophate and DFP were potent inhibitors of [3H]CD binding, as were the active "oxon" forms of parathion, malathion, and disulfoton. The parent "thio" forms of these insecticides, however, were much less effective in competing for [3H]CD binding. A similar pattern of potency was observed for the inhibition of brain AChE activity. A strong correlation was found between the ability of a compound to inhibit AChE activity and the ability to compete with [3H]CD binding. These data suggest that the biological effects of cholinesterase-inhibiting compounds may be due to more than their ability to inhibit AChE.

We measured in nine patients, poisoned by organophosphorus agents (ethyl parathion, ethyl and methyl parathion, dimethoate, or bromophos), erythrocyte and serum cholinesterase activities, and plasma concentrations of the organophosphorus agent. These patients were treated with pralidoxime methylsulphate (Contrathion), administered as a bolus injection of 4.42 mg.kg-1 followed by a continuous infusion of 2.14 mg.kg-1/h, a dose regimen calculated to obtain the presumed "therapeutic" plasma level of 4 mg.l-1, or by a multiple of this infusion rate. Oxime plasma concentrations were also measured. The organophosphorus agent was still detectable in some patients after several days or weeks. In the patients with ethyl and methyl several days or weeks. In the patients with ethyl and methyl parathion poisoning, enzyme reactivation could be obtained in some at oxime concentrations as low as 2.88 mg.l-1; in others, however, oxime concentrations as high as 14.6 mg.l-1 remained without effect. The therapeutic effect of the oxime seemed to depend on the plasma concentrations of ethyl and methyl parathion, enzyme reactivation being absent as long as these concentrations remained above 30 micrograms.l-1. The bromophos poisoning was rather mild, cholinesterases were moderately inhibited and increased under oxime therapy. The omethoate inhibited enzyme could not be reactivated.

Organophosphate transport through the placenta was investigated in an in-vitro placental perfusion system. The system consisted of maternal and fetal reservoirs in which Krebs Ringer bicarbonate buffer with heparin, albumin and glucose was circulated at a constant pH, temperature and pO2. Parathion was analysed by means of gas chromatography with a N-P detector. 14C Antipyrine, a lipid soluble salt, was used as an internal standard, which allowed for the difference in placental size and permeability. A certain amount of parathion passed the placenta and reached the fetal compartment. Glucose consumption was not influenced by the introduction of parathion; neither was the water content of the placental tissue. Acetylcholinesterase activity in placental tissue decreased 50%. The amount of parathion transferred was not negligible and could have caused damage to a fetus.

Selection of field populations originating from several countries allowed us to isolate 13 strains of Drosophila melanogaster resistant to parathion. In vitro studies of acetylcholinesterase inhibition by paraoxon have been carried out on purified enzymes: most of the resistant strains harbor an altered acetylcholinesterase. Enzymes with higher resistance levels have been characterized with respect to their cross-resistance toward several insecticides. The patterns obtained have permitted us to group them and to delineate four categories. The existence of four distinct types of protein suggests that several mutations of acetylcholinesterase are responsible for insecticide resistance in Drosophila.

Using pharmacokinetic data from healthy human volunteers in a bicompartmental pharmacokinetic model, a repeated dose scheme for pralidoxime methylsulphate (Contrathion) was developed producing plasma levels remaining above the assumed "therapeutic concentration" of 4 mg.l-1. Using the same data, it was found that a concentration of 4 mg.l-1 could also be obtained by a loading dose of 4.42 mg.kg-1 followed by a maintenance dose of 2.14 mg.kg-1.h-1. In order to study the pharmacokinetic behaviour of pralidoxime in poisoned patients, this continuous infusion scheme was then applied in nine cases of organophosphorus poisoning (agents: ethyl parathion, ethyl and methyl parathion, dimethoate and bromophos), and the pralidoxime plasma levels were determined. The mean plasma levels obtained in the various patients varied between 2.12 and 9 mg.l-1. Pharmacokinetic data were calculated, giving a total body clearance of 0.57 +/- 0.27 l.kg-1.h-1 (mean +/- SD), an elimination half-life of 3.44 +/- 0.90 h, and a volume of distribution of 2.77 +/- 1.45 l.kg-1.

Although acetylcholinesterase is the target molecule of organophosphate poisoning, it is not always assayed in clinical evaluations which include only the determination of plasma or serum cholinesterase. In this paper we present observations on workers exposed to, or poisoned by, ethylparathion. Acetylcholinesterase decreased earlier and more intensely than cholinesterase, with the suggestion of an initial increase of acetylcholinesterase activity in newly exposed, workers. A simplified standard Ellman assay of total acetylcholinesterase activity of hemolyzed total blood correlated with that of washed erythrocyte acetylcholinesterase. All results were standardized to both red blood cell and hemoglobin concentration. Normal values in a group of unexposed subjects were acetylcholinesterase: 1225 +/- 181 nU x 10/RBC and 39.30 +/- 5.05 U/g Hb for men, 1321 +/- 234 nU x 10/RBC and 42.57 +/- 6.85 U/g Hb for women. Differences between total and erythrocyte acetylcholinesterase were not statistically significant. Plasma cholinesterase appeared to be decreased in pregnancy and increased in anesthesia, liver and kidney disease and neuropathologic conditions attributed to metal poisoning while total acetylcholinesterase was unaffected. The determination of both cholinesterase and acetylcholinesterase assists the evaluation of individuals exposed to or poisoned by organophosphate, the differentiation of other conditions affecting cholinesterase and the recognition of genetically atypical cholinesterase.

Between 1978 and 1986, 305 samples of apples were monitored for the residues of a wide range of pesticides used in their production. Three (1%) contained residues above the maximum residue limits (MRL) permitted under the Canadian Food and Drug Act and regulations; two involved phosalone at 5.9 and 6.2 mg/kg respectively and one involved diphenylamine at 6.7 mg/kg when the MRL was 5.0 mg/kg for both compounds. Low residues of dicofol, endosulfan, phosalone, phosmet, captan, daminozide and diphenylamine were frequently found; however they were well below the MRLs. These residue levels were correlated with survey data on the areas of the apple crop treated with specific pesticides. Residues of carbaryl, diazinon, ethion, azinophosmethyl, parathion, and dithiocarbamate fungicides were found occasionally; all were well below the MRLs and correlated with the pattern of use. No residues of PCB were found to a limit of detection of 0.01 mg/kg.

An HPLC method for the simultaneous detection of six organophosphorus pesticides (Dimethoate, Ethion, Malathion, Phorate, Phosalone and Parathion) on a Zorbex ODS column using methanol + water (80:20) as solvent is described.

Bobwhite quail eggs were injected at 48 or 72 hr of incubation with various doses of the organophosphate (OP) insecticides diazinon or parathion and the embryos were examined after an additional 48 hr of incubation by both histological and cartilage-staining methods. Bobwhite embryos did not display the notochordal folding or vascular enlargement reported for OP-injected chicken embryos. Cartilage staining of embryos injected with insecticide at 72 hr of incubation and recovered at day 12 of incubation revealed severe shortening and contortion of the vertebral axis, as well as tibiotarsal, rib, and sternum defects. Parathion was more potent in causing skeletal defects than diazinon. No type I defects (micromelia, parrot beak) were detected. Radiometric acetylcholinesterase (AChE) assays of whole embryo homogenates were performed for day 6, 9, and 12 diazinon-injected and control embryos. Diazinon effected drastic reductions in AChE activity. Although the AChE and axial skeletal responses of bobwhite embryos to OP injection are similar to those reported in the literature for other species, some major differences in the bobwhite response were noted: namely, the absence of notochordal folding in the young bobwhite embryo and the absence of type I defects at day 12. These differences suggest that further studies with the bobwhite quail would be useful in clarifying the mechanisms involved in OP-induced teratogenesis.

Responses of Paramecium caudatum, a ciliated protozoan, to acute exposures of certain organic solvents and organophosphorus insecticides (OPI) were studied by determining their lethal concentration (10 min-LC100) and median lethal concentration (4 h-LC50). The solvents and OPI evoked a distinct sequence of responses. Among the five solvents tested, acetone proved most toxic [LC-2.9% and LC50-0.68% (v/v)], while dimethyl sulphoxide (DMSO) showed least toxicity [LC-11.0% and LC50-3.16% (v/v)]. The order of toxicity of solvents was: acetone greater than ethanol greater than methanol greater than N, N-dimethylformamide greater than dimethylsulphoxide. The LC values of six OPI dissolved in either acetone or DMSO indicated that they were more toxic when dissolved in acetone and least toxic in DMSO. Among the OPI, bromophos proved most toxic (LC-10 ppm) while malathion showed least toxicity (LC-200 ppm) in DMSO. The order of toxicity of OPI was: bromophos greater than pirimiphos-methyl greater than parathion methyl greater than dichlorvos greater than fenitrothion greater than malathion. The 4 h-LC50 values computed for bromophos and malathion (dissolved in DMSO) were 575 ppb and 19.9 ppm, respectively, indicating the high susceptibility of P. caudatum to bromophos. The results indicate that the Paramecium toxicity assay could be used as a complementary system to rapidly elucidate the cytotoxic potential of compounds.

The postmortem distribution of acetylcholinesterase (AChE) inhibition was studied in the brains of 2 victims of lethal parathion intoxication and 2 control brains matched for age and sex. AChE activity in discrete brain regions was studied by quantitative histochemistry of 40-micron-thick sagittal or coronal cryostat sections from the 4 brains. Inhibition of human brain AChE by parathion is regionally selective. The biggest decreases (60-85%) were observed in the cerebellum, some thalamic nuclei, and the cortex. Only a moderate decrease (10-30%) was observed in the substantia nigra and basal ganglia, and no effect was seen in white matter. Detailed knowledge of the brain regions affected by parathion poisoning may explain some of the clinical manifestations of organophosphate poisoning.

The regional distribution of AChE inhibition by parathion in the human brain was examined in a comparative study of the brains of 2 victims of lethal parathion intoxication and 2 control brains matched for age and sex. AChE activity in discrete brain regions was studied by quantitative histochemistry of 40 microns-thick sagittal or coronal cryostat sections from the 4 brains. The inhibition of human brain AChE by parathion is regionally selective. The biggest decreases were observed in the cerebellum, some thalamic nuclei and cortex. Only a moderate decrease (10-30%) was observed in the substantia nigra and basal ganglia, while no effect at all was seen in white matter regions. Detailed knowledge of the brain regions affected by parathion poisoning may explain some of the clinical manifestations of organophosphate poisoning.

The neurotoxicities of single doses of a chemical warfare agent VX [phosphonothioic acid, methyl-S-(2-[bis(1-methylethyl)amino/ethyl) O-ethyl ester], a metabolite of the agricultural chemical parathion, paraoxon, PO (phosphonothioic acid, diethyl paranitrophenyl ester), and the known neuropathic agents DFP] phosphorofluoridic acid, bis(1-methylethyl) ester] and TOCP (phosphoric acid, tri-o-tolyl ester) were compared in the chicken. Single injections (subcutaneous, sc) of VX as high as 150 micrograms/kg (5 times the LD50, intramuscular, im) were tolerated by laying tens if atropine and 2-pralidoxime were used as antidotes before and immediately after injection. The 150 of VX for inhibition of chicken brain acetylcholinesterase was approximately 5 X 10(-10). Plasma acetylcholinesterase, but not butyrylcholinesterase, was depressed 2 h after injections of 2-20 micrograms VX/kg im without antidotes. Levels of plasma enzymes such as creatine kinase, indicative of tissue damage, were increased after exposure to both VX and PO. Injections of up to 150 micrograms/kg of VX with antidotes did not cause locomotor or histological signs of organophosphorus-induced delayed neuropathy, but single injections of 400 mg TOCP/kg did.

In developing countries, extensive use of pesticides to meet with increased agricultural needs is inevitable and the indiscriminate use has led to several toxicological implications in humans. The toxic effects, however, to a large extent depend on the nutritional status of the individuals. In the present work, the hepatic susceptibility to pesticide toxicity has been studied in experimental animals maintained on diets containing different levels of protein for a period of 3 weeks. Along with protein deprivation, the rats were also exposed to three organophosphorus pesticides, viz., parathion, malathion, and phosalone, individually at various doses for the same time period. Phosphatases, the functionally important enzymes of the liver, were estimated and the results obtained indicated that protein deprivation further aggravated the pesticide-induced effects on the hepatic phosphatases.

A screening method has been developed for determining organophosphorus pesticides at ng/L levels in drinking water. Sixteen organophosphorus pesticides, diazinon, diazinon-oxon, dimethoate, ronnel, beta-phosphamidon, methyl parathion, ethyl parathion, malathion, chlorpyrifos, fenitrothion, ruelene, methidathion, ethion, EPN, phosalone, and phosmet, were extracted by Amberlite XAD-2 resin from 100 and 200 L drinking water previously spiked with these pesticides. The pesticides were eluted from the XAD-2 resin with acetone-hexane (15+85). The concentrated extract was analyzed by gas chromatography using a nitrogen-phosphorus selective detector and by gas chromatography-mass spectrometry using selected ion monitoring. Recoveries at the 10 and 100 ng/L spiking levels were greater than 90%, except recoveries for dimethoate and phosphamidon were 37 and 42%, respectively. The analysis of 300 L Ottawa tap water showed no detectable amounts (less than 1 ng/L) of any of the 16 organophosphorus pesticides.

The development of chemical control of Musca domestica on Danish farms 1945--72 is outlined. It has been strongly influenced by successive development of resistance and failure of control by one insecticide after another. The chlorinated hydrocarbons used as residual sprays failed 1947--51. Organophosphorus compounds (OPC) were widely used from 1953, first as strips impregnated with parathion and residual sprays with diazinon. Resistance to OPC was first found in 1955, diazinon was given up in 1957--59 and parathion strips failed in the early '60's. Trichlorfon paint-on baits were widelyused 1958--64 and serious resistance did not appear until 1967, induced by selective pressure of fenthion and dimethoate used as residual sprays. High resistance to the contact effect of trichlorfon now occurs everywhere in Denmark. However, trichlorfon baits are still able to kill many flies. Residual sprays with fenthion, ronnel and fenitrothion were used to some extent 1960--70, but increased resistance reducing the residual effect developed in 2--3 years. Dimethoate was used on the majority of farms 1965--72. It was very effective the first years and resistance increased slowly until 1971--72, when high to extreme dimethoate-resistance became general on Danish farms. This was associated with high resistance to other OPC for fly control, e.g. fenthion, fenitrothion, bromophos, and tetrachlorvinphos, and to carbamates, with the result that no generally effective residual sprays were available. In 1971--72 frequent treatments with synergized pyrethroids have been tried. However, the method is often expensive, and serious resistance problems have appeared on a few farms. In this situation preventive, sanitary measures to eliminate or reduce fly breeding in manure are becoming decisive again, but difficult to practise due to lack of farm labour. The extreme Danish situation is compared with those in other areas, and probable reasons for differences in resistance and control problems are discussed, as well as possibilities for strategies to reduce resistance development.

Alle als lnsektizide verwendbaren organischen Phosphorsaureester wie E 6O5 oder Gusathion entsprechen einem ganz bestirnmten Aufbauschema. Von besonderem lnteresse sind die systernisch wirkenden Systox-Preparate. Die neu entwickelten lnsektizide zeigen die Tendenz, die allgemeingiftigeren Phosphor-Verbindungen durch biologisch selektiv wirkende zu ersetzen https://onlinelibrary.wiley.com/doi/epdf/10.1002/ange.19570690304