Inhibition of rat platelet 5-hydroxytryptamine uptake by chlorpyrifos and carbaryl

The organophosphate insecticide chlorpyrifos and the carbamate insecticide carbaryl were investigated in adult male rats in terms of their effects on the activity of brain monoamine oxidase-A (MAO-A) activity and on the plate let uptake of 5-hydroxytryptamine (5-HT). The activities of brain acetylcho linesterase (AChE) and plasma butyrylcholinesterase (BuChE) were also deter mined. For each compound two different dosage regimens were employed. In th e acute study, chlorpyrifos or carbaryl was administered at a single intrap eritoneal dose of 100 mg/kg or 50 mg/kg. respectively. In the subacute stud y, chlorpyrifos was injected at a daily dose of 20 mg/kg for 7 days, while carbaryl was given at a daily dose of 10 mg/kg for 14 days. Acute chlorpyri fos administration produced a 85.01% inhibition of AChE and a 43.4% inhibit ion of BuChE but had no effect on MAO-A activity and 5-HT uptake. In contra st, subacute chlorpyrifos exposure caused a 94.96%, inhibition of AChE and a 85.8% inhibition of BuChE and, also, elicited a significant (35.02%) redu ction in the platelet uptake of 5-HT. MAO-A activity was not affected. Acut e carbaryl administration produced a 56.38% AChE inhibition and a 55.95% Bu ChE inhibition and also caused a significant (26.36%) decrease in 5-HT upta ke but no change in MAO-A. Subacute carbaryl exposure failed to affect sign ificantly any of the biochemical parameters determined. Interference with t he 5-HT system by chlorpyrifos and carbaryl could contribute to the toxicit y of these pesticides.