Inhibitor Report for: Atropine

OBJECTIVE To determine whether serum cholinesterase level has a prognostic value in human acute organophosphorus poisoning. DESIGN: Cohort (prospective) prognosis study. SETTING: Medical ICU at University Hospital. PATIENTS: Thirty consecutive patients admitted to the ICU for acute organophosphate poisoning. MEASUREMENTS: Serum cholinesterase level was measured in all patients at the time of hospital admission. Severity of intoxication was assessed by the total dose of atropine required to relieve poisoning manifestations, the Simplified Acute Physiology Score, the need for assisted ventilation, and by a specific grading system previously validated that identified two groups of patients: group 1 (low severity, n = 18) and group 2 (high severity, n = 12). RESULTS: Serum cholinesterase level did not correlate with the total dose of atropine or with the Simplified Acute Physiology Score. Mean serum cholinesterase level was not significantly different between group 1 and group 2 patients (448 +/- 409 U/L in group 1 compared with 611 +/- 575 U/L in group 2 (p = NS); it was also not significantly different between patients with and without mechanical ventilation support (567 +/- 571 vs 470 +/- 409, respectively). CONCLUSION: Serum cholinesterase levels have no prognostic value in acute organophosphate poisoning. Thus, a grading system to identify high-risk patients based on this measurement is most likely unreliable.

Study was conducted to find out the correlation between red blood cholinesterase (RBC ChE) and plasma butyryl cholinesterase (BCHE) activities and toxic signs of oral methylparathion (MPT) and their recovery pattern with or without atropine treatment in female rats. Enzyme activity was estimated before and after an oral dose of MPT (7.5 mg/kg-1) at various time intervals upto 120 hr. Antidote groups received atropine (10 mg/kg-1, i.p.), either alone or with diazepam (2.5 mg/kg-1, i.p.), at the onset of toxic signs. Inhibition of enzyme activity served as definite index of acute toxicity of MPT. RBC ChE activity correlated with the intensity of toxic signs in no-antidote rats, while in atropine treated groups, there was no correlation. BCHE levels did not correlate with toxic signs in any of the groups except in the fatal group. The resynthesis of both the enzymes was complete in 120 hr study and did not synchronize with the recovery pattern of animals from toxic signs. Compared to BCHE, RBC ChE activity was found to be a more sensitive indicator for the diagnosis of severity of MPT toxicity.

The inhibitory effect of paraquat on cholinesterase activity was investigated in comparison with four paraquat derivatives, six monoquaternary ammoniums and six anticholinergic drugs. Inhibitor concentrations to cause 50% inhibition (I50) and Hill coefficients for three enzymes, human erythrocyte acetylcholinesterase (AChE), Electrophorus electricus AChE and human plasma butyrylcholinesterase (BCHE) were measured. The results obtained were as follows. The I50 for erythrocyte AChE was similar to the I50 for eel AChE. Secondary to edrophonium, diethylparaquat, paraquat, morfamquat and monoquat showed lower I50 for AChE, and possessed higher inhibition selectivity (IS), expressed as the ratio of I50 for BCHE to I50 for erythrocyte AChE. However, diquat showed higher I50 for AChE and lower IS, similar to the other monoquaternary ammoniums. A negative correlation was observed between log [I50 for erythrocyte AChE] and log [IS], among paraquat and its derivatives, monoquaternary ammoniums and anticholinergic drugs, respectively. With respect to Hill coefficients, these inhibitors could be classified into four groups, [1] competitive inhibitors: diquat, edrophonium, choline, tetramethylammonium and trimethylphenylammonium, [2] inhibitors showing negative cooperativity: paraquat, diethylparaquat, morfamquat, d-tubocurarine, atropine, gallamine and nicotine, [3] moderate type inhibitors: monoquat, hexamethonium and decamethonium. [4] the other type inhibitors showing positive cooperativity for erythrocyte AChE: tetraethylammonium and ethyltrimethylammonium.

The rates of inhibition of mouse acetylcholinesterase (AChE) (EC 3.1.1.7) by paraoxon, haloxon, DDVP, and enantiomers of neutral alkyl methylphosphonyl thioates and cationic alkyl methylphosphonyl thiocholines were measured in the presence and absence of AChE peripheral site inhibitors: gallamine, D-tubocurarine, propidium, atropine and derivatives of coumarin. All ligands, except the coumarins, at submillimolar concentrations enhanced the rates of inhibition by neutral organophosphorus compounds (OPs) while inhibition rates by cationic OPs were slowed down. When peripheral site ligand concentrations extended to millimolar, the extent of the enhancement decreased creating a bell shaped activation profile. Analysis of inhibition by DDVP and haloxon revealed that peripheral site inhibitors increased the second order reaction rates by increasing maximal rates of phosphylation.

Organophosphorus nerve agents are still in use today in warfare and as terrorism compounds. Classical emergency treatment of organophosphate poisoning includes the combined administration of a cholinesterase reactivator (an oxime), a muscarinic cholinergic receptor antagonist (atropine) and a benzodiazepine anticonvulsant (diazepam). However, recent experiments with primates have demonstrated that such treatment, even when administered immediately after organophosphate exposure, does not rapidly restore normal electroencephalographic (EEG) activity and fails to totally prevent neuronal brain damage. The objective of this study was to evaluate, in a realistic setting, the therapeutic benefit of administration of GK-11 (gacyclidine), an antiglutamatergic compound, as a complement to the available emergency therapy against organophosphate poisoning. GK-11 was injected at a dose of 0.1 mg/kg (i.v) after a 45-min latency period to heavily intoxicated (8 LD50) primates. Just after intoxication, man-equivalent doses of one autoinjector containing atropine/pralidoxime/diazepam were administered. The effects of GK-11 were examined on survival, EEG activity, signs of toxicity, recovery after challenge and central nervous system histology. The present data demonstrate that treatment with GK-11 prevents the mortality observed after early administration of classical emergency medication alone. EEG recordings and clinical observations also revealed that GK-11 prevented soman-induced seizures and motor convulsions. EEG analysis within the classical frequency bands (beta, theta, alpha, delta) demonstrated that central activity was totally restored to normal after GK-11 treatment, but remained profoundly altered in animals receiving atropine/pralidoxime/diazepam alone. GK-11 also markedly accelerated clinical recovery of soman-challenged primates. Lastly, this drug totally prevented the neuropathology observed 3 weeks after soman exposure in animals treated with classical emergency treatment alone. GK-11 represents a promising adjuvant therapy to the currently available emergency polymedication to ensure optimal management of organophosphate poisoning in man. This drug is presently being evaluated in a human clinical trial for a different neuroprotective indication.

BACKGROUND: Imbalance in cardiac sympathetic tone causes prolongation of the QTc interval of the ECG. On the other hand, impairment of the parasympathetic control of the heart rate caused by anticholinesterase-anticholinergic combinations might also affect the cardiac sympathetic tone and hence the QTc interval of the ECG. The main purpose of the present study was to compare the effects of four anticholinesterase-anticholinergic combinations used for the antagonism of the neuromuscular block on the QTc interval of the ECG, heart rate and arterial pressure. METHODS: Eighty-four ASA class I-II patients with a mean age of 32 to 37 yr undergoing otolaryngological surgery were randomly allocated to one of the following groups: neostigmine 40 microg/kg+glycopyrronium 8 microg/kg (Ne-Glyc), neostigmine 40 microg/kg+atropine 20 microg/kg (Ne-Atr), edrophonium 200 microg/kg+atropine 300 microg (Edr-Atr (1)), edrophonium 500 microg/kg+atropine 7 microg/kg (Edr-Atr (2)). QTc interval and heart rate were measured by a signal processing method based on an IBM/PC/xT-compatible microcomputer and arterial pressure with a sphygmomanometer at 1-min intervals up to 10 min after the injection of the drugs and immediately and 2 min after extubation. The ECG, lead II, was continuously recorded. Neuromuscular block was measured by a Datex relaxograph. RESULTS: In all groups, the most pronounced increase in both QTc interval, heart rate and arterial pressure occurred 1 min after the study drugs and immediately after extubation. In all groups, the mean QTc intervals at 1 and 2 min after the study drugs and after extubation were longer than the upper limit of the normal range (440 ms). Junctional rhythm occurred in 1 to 3 patients in all other groups with the exception of the Edr-Atr(1) group in which no cardiac arrhythmias occurred. At 1 min, the heart rate in the Ne-Atr group was at a significantly higher level than that in the Ne-Glyc group. From 3 to 6 min, the heart rate in the Edr-Atr(2) group and at 3 min in the Edr-Atr(1) group was at a lower level than the heart rate in the Ne-Glyc group. CONCLUSIONS: On the basis of the present results, anticholinesterase-anticholinergic combinations should be avoided in patients having a long QT interval syndrome or a prolonged QT interval from other causes. In addition, the cardiovascular stimulation caused by tracheal extubation should also be avoided in these patients.

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.

To investigate transsynaptic effects on peptides of adrenal chromaffin cells in the rat, presynaptic sympathetic terminals were destroyed by intravenous injection of monoclonal antibodies to acetylcholinesterase. At several times thereafter, neuropeptide Y (NPY)-like immunoreactivity (NPY-IR) and methionine-enkephalin-like immunoreactivity (Met-Enk-IR) were measured by radioimmunoassay. Within 2 days of antibody injection, adrenal Met-Enk-IR increased five- to 10-fold and NPY-IR increased 50%. These effects were accompanied by large increases in proenkephalin A mRNA assayed by polymerase chain reaction. The peptide responses could reflect either an acute activation, as presynaptic terminals degenerated, or a chronic synaptic inactivation after terminal degeneration. To test the possibilities, muscarinic and nicotinic receptors were inhibited by repeated injection of atropine (1 mg/kg) and chlorisondamine (5 mg/kg). Measurements of urinary free catecholamine excretion showed that this treatment prevented the paroxysmal release of norepinephrine and reduced the release of epinephrine that normally followed injection of acetylcholinesterase antibodies. When the drugs were given alone for 2 or 4 days, adrenal Met-Enk-IR increased modestly and NPY-IR remained steady or declined. When given together with acetylcholinesterase antibodies, the cholinergic antagonists blocked the increase of NPY-IR but not Met-Enk-IR. Adding naloxone (1 mg/kg) to the treatment regimen enhanced the blockade of epinephrine excretion and largely prevented the antibody-induced increase in Met-EnK-IR. These findings indicate that adrenal NPY and enkephalin are not regulated identically. Adrenal NPY behaves as though controlled by transsynaptic cholinergic input. On the other hand, adrenal enkephalin may be regulated by additional or different mechanisms, possibly involving peptidergic transmission or synaptic inactivation.

Neurotransmitters have been reported to regulate neurite outgrowth in several vertebrate and nonvertebrate species. In this study, cultures of isolated embryonic day 12 (E12) chick sympathetic neurons were grown in the presence of cholinergic receptor agonists or antagonists. Both ACh and the nonhydrolyzable cholinergic agonist carbamylcholine (CCh) inhibited neurite outgrowth. ACh (0.1-1.0 mM) decreased the percentage of neurons bearing neurites, but had no significant effect on cell survival. The effect of ACh was increased in the presence of the cholinesterase inhibitors BW284C51 (1 microM), Tacrine (20 microM), and edrophonium (200 microM). Neurite outgrowth was strongly inhibited by the muscarinic receptor agonist oxotremorine (5-100 microM) and weakly inhibited by nicotine (50 nM to 10 microM). The inhibitory effect of CCh was decreased by the muscarinic receptor antagonist atropine (10 microM), demonstrating that the effect of CCh on neurite outgrowth was mediated, at least in part, through a muscarinic receptor. The possibility that AChE can influence neurite outgrowth directly, through a noncatalytic mechanism, was also examined. When dissociated chick brain or sympathetic neurons were grown on plates precoated with purified AChE, neurite outgrowth was strongly stimulated. However, the neurite outgrowth-promoting effect of AChE was strictly dependent upon the presence of substratum-bound heparan sulfate proteoglycans (HSPG). Pretreatment of AChE with diisopropylfluorophosphate to inhibit the esterase activity did not abolish this effect, suggesting that the neurite outgrowth-promoting effect of AChE was associated with a noncatalytic mechanism, a view supported by the observation that soluble AChE had no effect on neurite outgrowth.

During the past decade the oxime HI 6(1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]-2- [(hydroxyimino)methyl] pyridinium dichloride) was shown to improve survival in nerve agent poisoning (in combination with atropine). Recent studies indicate, that HL 7 (1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]-2,4-bis [(hydroxyimino)methyl] pyridinium diiodide or dimethanesulfonate) is also an effective antidote in nerve agent poisoning but, with both oximes, data on restoration of respiration and circulation are scarce. The ability of HL 7 or HI 6 with atropine to improve the respiratory and circulatory function in sarin-poisoned guinea-pigs was therefore investigated. Female Dunkin-Hartley guinea-pigs were anaesthetised with urethane (1.8 g/kg) and the arteria carotis, vena jugularis and trachea were cannulated. After baseline measurements the animals received 100 or 200 micrograms/kg sarin, and 2 min later the antidotes (all i.v.): 10 mg/kg atropine sulfate or a combination of atropine and HL 7 or HI 6 (30 mumol/kg, each). Respiratory and circulatory parameters were recorded for the whole experimental period of 60 min or until the death of the animal. Brain and diaphragm acetylcholinesterase (AChE) activity was determined in each animal after the experiment. Poisoning by sarin resulted in a rapid respiratory arrest within 5 min. Atropine treatment was only partially effective in improving respiration after 100 micrograms/kg sarin but was ineffective after 200 micrograms/kg sarin. Therapy of sarin-poisoned animals with atropine plus oxime further improved respiration to various extents, restored circulation and increased survival time, HL 7 being more effective than HI 6. Diaphragm and brain AChE were reactivated by HL 7 and, to a minor extent, by HI 6. The results of this investigation suggest, that at equimolar doses (30 mumol/kg) the new bispyridinium dioxime HL 7 has a higher therapeutic efficacy in sarin-poisoned guinea-pigs when compared to HI 6 (both in combination with atropine).

Three experiments are reported: 1) a feasibility study on using laboratory primates repeatedly in behavioral toxicity studies of organophosphate (OP) agents or of chemical countermeasures against OPs; 2) a study of the efficacy of pyridostigmine pretreatment and 2-PAM therapy; and 3) a study to determine the effects of these treatments on soman-induced cholinesterase (ChE) inhibition and its recovery. In rhesus monkeys, three repeated acute low-dose (2.1 to 2.8 micrograms/kg) soman exposures, separated by intervals > 5 weeks, did not change baseline compensatory tracking performance or the soman ED50. Atropine therapy (97 micrograms/kg) alone had no effect on soman ED50. Addition of pyridostigmine pretreatment (150 micrograms/kg) and 2-PAM therapy (17 mg/kg) to atropine therapy increased the soman ED50 for a performance decrement from 2.27 micrograms/kg to 2.58 micrograms/kg, an insignificant protective effect. At the soman ED50 for behavioral decrements, pyridostigmine pretreatment increased the inhibition of serum ChE observed immediately after soman exposure, but reduced the extent of permanent inhibition. The 2-PAM therapy reduced serum ChE inhibition from about 80% to less than 70%. These effects on the time course of ChE inhibition following soman exposure appear to combine additively. These chemical countermeasures do not prevent soman-induced performance decrements, even though they are effective in protecting lives after much higher doses. The soman doses used produce only small, transient performance decrements; animals so exposed can, thus, be used repeatedly in such studies.

OBJECTIVE To study the clinical profile and cholinesterase levels of subjects of organophosphate and carbamate poisoning and to identify those subjects who would require ventilatory support. DESIGN: Prospective, observational study. SETTING: Intensive care unit of a tertiary care urban hospital. SUBJECTS: Fifty-two patients admitted with a diagnosis of organophosphate or carbamate poisoning. OUTCOME MEASURES: Subject survival and ventilator requirement. INTERVENTION: Treatment with atropine and pralidoxime and mechanical ventilation for patients with respiratory failure. Clinical features were monitored at every stage, and blood for plasma and red blood cell cholinesterase levels was collected on admission. RESULTS: According to the ingested poison, subjects were divided into four groups: organophosphates (13 subjects), mixed organophosphate and carbamate (18), carbamates (13), and a fourth miscellaneous group (8). Dyspnea and vomiting were the most common symptom and miosis and cyanosis were the most frequently observed signs. Plasma and red cell cholinesterase levels were lowest in the mixed poison group and highest in the carbamate group. Twenty-seven subjects developed Type I respiratory failure and 7 had Type II respiratory failure. Mechanical ventilation was required in 31 subjects. Overall 33 subjects survived. A scoring system, on a point scale of 16, was developed using miosis, unconsciousness, fasciculations, and plasma cholinesterase levels to predict ventilator requirement. CONCLUSION: This study helps to identify at an early stage those patients with organophosphate or carbamate poisoning who would ultimately require ventilatory support. We found miosis, unconsciousness, fasciculations, and a low plasma cholinesterase level to be of greatest predictive value.

Insecticide poisoning is an increasing event which requires a thorough knowledge base for diagnosis and management. Awareness of the importance of decontamination is fundamental not only in the prehospital care phase but also in the emergency department. A thorough knowledge of the essentials of emergency and critical care is indispensable for the management and support of ventilatory and circulatory functions. Specific antidotal therapy utilizing atropine and pralidoxime is usually necessary in the immediate care of acute cases. In addition, use of pralidoxime after acute exposure may contribute to a beneficial outcome. Appropriate laboratory determinations in the acute phase are necessary parameters for successful outcomes. The use of cholinesterase determinations for diagnostic and prognostic purposes is discussed.

OBJECTIVE To determine whether serum cholinesterase level has a prognostic value in human acute organophosphorus poisoning. DESIGN: Cohort (prospective) prognosis study. SETTING: Medical ICU at University Hospital. PATIENTS: Thirty consecutive patients admitted to the ICU for acute organophosphate poisoning. MEASUREMENTS: Serum cholinesterase level was measured in all patients at the time of hospital admission. Severity of intoxication was assessed by the total dose of atropine required to relieve poisoning manifestations, the Simplified Acute Physiology Score, the need for assisted ventilation, and by a specific grading system previously validated that identified two groups of patients: group 1 (low severity, n = 18) and group 2 (high severity, n = 12). RESULTS: Serum cholinesterase level did not correlate with the total dose of atropine or with the Simplified Acute Physiology Score. Mean serum cholinesterase level was not significantly different between group 1 and group 2 patients (448 +/- 409 U/L in group 1 compared with 611 +/- 575 U/L in group 2 (p = NS); it was also not significantly different between patients with and without mechanical ventilation support (567 +/- 571 vs 470 +/- 409, respectively). CONCLUSION: Serum cholinesterase levels have no prognostic value in acute organophosphate poisoning. Thus, a grading system to identify high-risk patients based on this measurement is most likely unreliable.

Study was conducted to find out the correlation between red blood cholinesterase (RBC ChE) and plasma butyryl cholinesterase (BCHE) activities and toxic signs of oral methylparathion (MPT) and their recovery pattern with or without atropine treatment in female rats. Enzyme activity was estimated before and after an oral dose of MPT (7.5 mg/kg-1) at various time intervals upto 120 hr. Antidote groups received atropine (10 mg/kg-1, i.p.), either alone or with diazepam (2.5 mg/kg-1, i.p.), at the onset of toxic signs. Inhibition of enzyme activity served as definite index of acute toxicity of MPT. RBC ChE activity correlated with the intensity of toxic signs in no-antidote rats, while in atropine treated groups, there was no correlation. BCHE levels did not correlate with toxic signs in any of the groups except in the fatal group. The resynthesis of both the enzymes was complete in 120 hr study and did not synchronize with the recovery pattern of animals from toxic signs. Compared to BCHE, RBC ChE activity was found to be a more sensitive indicator for the diagnosis of severity of MPT toxicity.

In a guinea-pig model with on-line respiratory and circulatory monitoring the therapeutic efficacy of atropine, HL 7 and HI 6 in VX poisoning was compared. In female urethane-anaesthetized Pirbright-white guinea-pigs the a. carotis, v. jugularis and trachea were cannulated. After base line measurements the animals received VX (22.5, 45 or 90 micrograms/kg = 5, 10 or 20 x LD50) intravenously and 2 min. later the antidotes: HL 7 or HI 6 (30 mumol/kg, each) or atropine 10 mg/kg or a combination of atropine and one of the oximes (all intravenously). Respiratory and circulatory parameters were recorded for 60 min. or until death of the animal. Erythrocyte, brain and diaphragm acetylcholinesterase (AChE) activity was determined after the experiment. VX poisoning caused a rapid respiratory arrest within 4-5 min. Atropine treatment was effective in improving the respiratory function after VX, 22.5 micrograms/kg, but had only a small effect after the higher VX doses. The treatment of VX (10 or 20 x LD50) poisoned animals with oxime plus atropine improved respiration to various extents, restored circulation and prolonged the survival time, HL 7 being more effective than HI 6 after VX 90 micrograms/kg. Oximes alone were completely ineffective. Erythrocyte and diaphragm AChE was reactivated by HL 7 and, less effectively, by HI 6, while brain AChE remained almost completely inhibited in all groups. The results of this investigation demonstrate a reasonable efficacy of atropine after lower VX doses and of HL 7 and HI 6 (plus atropine) after high-dose VX poisoning, HL 7 being slightly more effective than HI 6.

To evaluate whether any degenerative changes affect the brain cholinergic systems during natural aging, we compared various cholinergic biochemical markers (number of muscarinic receptors, mAChR; choline acetyltransferase activity, ChAT; acetylcholinesterase activity, AChE; and sodium-dependent high affinity choline uptake) in the cortical (CR) and subcortical (SS) regions of the brains of aged (24 month) and young (2 month) rats. Using [3H]-quinuclidinyl benzilate ([3H]-QNB) as the ligand of muscarinic receptor binding, the numbers of mAChR decreased about 30% in both the CR and the SS of aged rats compared with those in young rats, while a significant age-related increase in the affinity of mAChR was observed. [3H]-QNB binding in both the young and aged rat brain was displaced markedly by pirenzepine, while [3H]-QNB binding in the SS of the aged rat brain was displaced at low concentrations of atropine. The Vmax values of ChAT and AChE also decreased about 20-30% compared with those of young rats. The sodium-dependent high affinity choline uptake was lower in the crude synaptosomal fraction prepared from aged rat brain than in young brain. Hemicholinium-3 inhibited the choline uptake in young rat brain at a concentration range of 1 microM-10 nM, but choline uptake in aged brain was insensitive to hemicholinium-3. These results indicate that natural aging brings about a diffuse and multiple depletion of various biochemical markers in cholinergic neurons.

The cholinergic activities of SR 46559A, 3-[N-(2 diethyl-amino-2-methylpropyl)-6-phenyl-5-propyl] pyridazinamine sesquifumarate, have been investigated in vitro and in vivo, in rodents. Using rat brain cortical membranes, SR 46559A was a competitive ligand (Ki = 112 nM) at muscarinic M1 receptors, its affinity for muscarinic M2 (cardiac) and M3 (glandular) receptors being 6-7 times lower. SR 46559A did not interact with brain nicotinic receptors and high affinity choline uptake sites nor did it inhibit brain acetylcholinesterase activity. In contrast to reference muscarinic agonists, SR 46559A (1 mM) did not inhibit the forskolin-induced activation of cAMP synthesis nor did it stimulate phosphoinositides breakdown in various brain preparations. However, this compound enhanced (+67% at 1 mM) diacylglycerol formation in rat striatal miniprisms, an effect fully reversed by atropine. As shown with reference agonists, SR 46559A inhibited (IC50 = 10 microM) the K(+)-evoked release of [3H]GABA from rat striatal slices and reduced at 0.5 and 1 microM, the population spike amplitude of the CA1 pyramidal cells induced by stimulation of the Schaffer's collateral commissural pathway in rat hippocampal slices. In mice, SR 46559A at a near lethal dose (200 mg/kg PO) did not induce the typical cholinergic syndrome nor did it modify at 30 mg/kg PO the oxotremorine-induced hypothermia. Like muscarinic agonists, SR 46559A (1 mg/kg PO) potentiated haloperidol-induced catalepsy in rats and inhibited (ED50 = 0.12 mg/kg PO) rotations induced in mice by intrastriatal injection of pirenzepine.

Various organophosphorus compounds with low acute toxicity levels are widely used as insecticides. Human acute poisoning by organophosphates has often occurred accidentally. We determined the activity and isoenzyme patterns of serum cholinesterase (ChE) obtained from 13 human patients who attempted suicide with various organophosphates, i.e. Fenitrothion, Malathion, Isoxathion, Pyridaphenthion and Trichlorfon, and studied on the changes in the activity and isoenzyme patterns of serum ChE after ingestion. The following results were obtained. 1) Twenty ChE isoenzyme bands from normal human serum were detected by electrophoretic separation on polyacrylamide gradient gel. The main bands in the ChE isoenzyme pattern in normal serum were bands 4 and 5 which had the highest activity of acetylcholinesterase (AChE) with a molecular weight of 600,000-800,000, and bands 7, 12, 14, 17 and 18. 2) Inhibition of serum ChE activity was more severe as the amount ingested increased in patients who took Fenitrothion and Malathion. Reactivation of serum ChE activity was very slow in patients treated with PAM (2-pyridine aldoxime methiodide) in the late stage of ingestion or whose symptoms reappeared. 3) There were no differences in the patterns of serum ChE isoenzyme by organophosphorus compound. Band 7 disappeared in the serum ChE isoenzyme of almost every patient, and bands 12, 18, 14 and 17 of the serum ChE isoenzyme disappeared successively with the decline of serum ChE activity. Only band 5 of the isoenzyme remained in cases who had serum ChE activity lower than 5% of normal. 4) All 13 patients were treated with PAM and atropine immediately after being admitted to hospitals. We could not clearly determine the efficacy of PAM on reactivation of serum ChE activity and isoenzyme, because it was impossible in human poisoning to compare PAM efficacy with no treatment and with pre- and post-PAM treatment. 5) The activity and isoenzyme patterns of serum ChE recovered rapidly after combined hemoperfusion and hemodialysis treatment (HP-HD treatment) of the patients poisoned with Malathion. But HP-HD treatment had no effect on poisoning by Fenitrothion and Isoxathion. These findings demonstrated the changes in the activity and isoenzyme pattern of serum ChE in patients poisoned with several organophosphates after PAM and HP-HD treatment.

The inhibitory effect of paraquat on cholinesterase activity was investigated in comparison with four paraquat derivatives, six monoquaternary ammoniums and six anticholinergic drugs. Inhibitor concentrations to cause 50% inhibition (I50) and Hill coefficients for three enzymes, human erythrocyte acetylcholinesterase (AChE), Electrophorus electricus AChE and human plasma butyrylcholinesterase (BCHE) were measured. The results obtained were as follows. The I50 for erythrocyte AChE was similar to the I50 for eel AChE. Secondary to edrophonium, diethylparaquat, paraquat, morfamquat and monoquat showed lower I50 for AChE, and possessed higher inhibition selectivity (IS), expressed as the ratio of I50 for BCHE to I50 for erythrocyte AChE. However, diquat showed higher I50 for AChE and lower IS, similar to the other monoquaternary ammoniums. A negative correlation was observed between log [I50 for erythrocyte AChE] and log [IS], among paraquat and its derivatives, monoquaternary ammoniums and anticholinergic drugs, respectively. With respect to Hill coefficients, these inhibitors could be classified into four groups, [1] competitive inhibitors: diquat, edrophonium, choline, tetramethylammonium and trimethylphenylammonium, [2] inhibitors showing negative cooperativity: paraquat, diethylparaquat, morfamquat, d-tubocurarine, atropine, gallamine and nicotine, [3] moderate type inhibitors: monoquat, hexamethonium and decamethonium. [4] the other type inhibitors showing positive cooperativity for erythrocyte AChE: tetraethylammonium and ethyltrimethylammonium.