Anticholinesterase Pesticides Research Articles

In vitro inhibition of goat brain acetylcholinesterase by pure and commerical anticholinesterase pesticides

In vitro inhibition of goat cerebellar acetylcholinesterase by pure and commerical anticholinesterase pesticides clearly indicates a remarkably high inhibitory effect of commerical carbamate and organophosphate pesticides containing a lower percentage of the respective active ingredients comparable to that of the known anticholinesterase agents such as DFP and physostigmine. It may be presumed that injudicious use of commercial formulations conduce severe toxicity in the nontarget mammalian species, namely, goat, and this response of the brain acetylcholinesterase may be utilized as a reliable bioindicator of pesticidal contamination of the terrestrial environment.

In vivo andIn vitro studies on synergism with anticholinesterase pesticides in the snailLymnaea acuminata

The synergistic effects of piperonyl butoxide (PB)2, sulfoxide (SU), and dimethyl amino aniline (DAA) used in conjunction with two organophosphate pesticides (phorate and formothion) and two carbamate pesticides (mexacarbate and carbaryl) were examined in terms of the LC50 and acetylcholinesterase (AChE) inhibition in the snailLymnaea acuminata. The three synergists reduced the LC50 of phorate, formothion, mexacarbate, and carbaryl at exposure periods ranging from 24 to 144 hr. PB and SU had strong synergistic action; DAA had little effect; the highest synergistic ratio (70) was found with carbaryl and PB. The synergists enhanced thein vitro inhibition of cholinesterase caused by the pesticides; the synergistic effect onin vitro inhibition, however, was lower, compared to the change in the LC50.

Water deprivation and food restriction on toxicity of parathion and paraoxon.

Three groups of rats were injected intraperitoneally with either parathion or paraoxon: (1) rats deprived of water for 48 hr, (2) rats allowed water ad lib but restricted in food intake to equal that consumed by water-deprived rats, and (3) controls. Following injection of parathion all groups showed a progressive decrease in enzymatic hydrolysis of acetylcholine over a 2-hr period. The decrease was significantly greater in food-restricted rats. Injection with paraoxon resulted in an immediate decrease in red cell cholinesterase activity, which remained low for 1 hr, but recovered thereafter. The esterase activity of both deprived groups was significantly lower than that of controls. These experiments suggest that persons subject to nutritional deficiency and water deficit may be abnormally susceptible to the effects of anticholinesterase pesticides.

Pharmacological studies on the molluscicidal activity of phorate on Pila globosa (Gastropoda).

Amongst heart, rectum and radula protractor muscles of Pila globosa, the heart showed a negative inotropic and negative chronotropic response while the rectum and radula protractor showed a positive tonotropic response to exogenously applied acetycholine (ACh). The anti-cholinesterase pesticide phorate substantially increased the response to ACh; at high doses it could also evoke cholinomimetic response from the heart. The anti-cholinesterase property of phorate gradually increased with an increase in its contact period to the tissue. The extent of alteration in ACh response caused by prior treatment with low and high doses of phorate were very similar, indicating that the efficacy of phorate is by and large time-dependent rather than dose-dependent. The effect of phorate remained irreversible even after prolonged washing. The mode of action of phorate has been discussed in the light of the above findings.

Determination of trace quantities of anticholinesterase pesticides

A procedure has been described which is applicable to the screening of large numbers of samples for anticholinesterase activity. The method is sufficiently sensitive to detect cholinesterase depression due to as little as 30 ppt paraoxon; 3 ppb malaoxon or 2 ppm of carbaryl in either ethylene glycol or water. While the method does not allow the absolute differentiation between compounds which might be present, some classification is possible, i.e., for compounds which must be activated before they possess anticholinesterase activity.

Behavioral and physiological effects of the cholinesterase inhibitor carbaryl (1-naphthyl methylcarbamate)

The anticholinesterase pesticide carbaryl was injected subcutaneously into rats lever-pressing for liquid reinforcement. During the test session a low intensity footshock accompanied each lever-press response with the carbaryl rats exhibiting a smaller response decrement due to the shock. In the second experiment, carbaryl injected rats displayed a higher behavioral threshold to footshock. These results appear to explain other studies in which animals given anticholinesterase agents show decreased efficiency in performing an avoidance response. Two additional experiments examined the effects of carbaryl on motivation for liquid. Rats lever pressing for liquid reinforcement on an FR-25 schedule were injected with carbaryl. It was found that the response onset after each reinforcement was significantly delayed in the carbaryl animals. This result, in addition to ad lib liquid consumption data, indicated a decreased drive for water in the carbaryl animals. Our findings, similar to results obtained using cholimolytics, presents an apparent discrepancy which we discuss in terms of (a) the necessity of having an optimum level of Acetylcholine (ACh) in the brain, (b) the possibility of a peripheral mechanism, or (c) the possibility of sympathomimetic effects of carbaryl.