Modification of carbaryl metabolism in rats with monoamine oxidase inhibitors.

The rate of carbaryl metabolism by rats was decreased by simultaneously administering drugs commonly referred to as monoamine oxidase inhibitors and by prolonged exposure of the animals to one of the drugs in the drinking water. Conjugative mechanisms of metabolism were affected most by the drugs although oxidative and hydroxylative metabolism rates were reduced to some degree. Decreasing the rate of metabolism resulted in a slower rate of excretion of the carbamate from rats treated with the drugs. Tranylcypromine at 50 mg/kg, e.g., reduced excretion of carbaryl-14C equivalents from rats by 50% during the 1st 48 hours after treatment. A rat intestine enzyme system, fortified with UDPGA, conjugated 1-naphthol but did not metabolize carbaryl. This in vitro conjugating system was inhibited by the monoamine oxidase inhibitors. The effect of these drugs on conjugation was not sufficient to suggest that they might enhance the action of pesticides under practical conditions. However, the data do demonstrate that conjugation enzyme systems are sensitive to certain foreign chemicals and that more effective inhibitors of conjugation could be important in the safety and efficacy of chemicals used to control insect pests.