Inhibition of cytochrome P450-dependent monooxygenases by an alkaloid fraction from Helietta apiculata markedly potentiate the hypnotic action of pentobarbital.

Crude alkaloid fraction (CAF) isolated from the leaves of Helietta apiculata showed the presence of furoquinolines. The extract was investigated to determine if it can enhance the sensitivity of the central nervous system (CNS) to the hypnotic action of pentobarbital. Administration of CAF to mice in a dose range of 300-500 mg/kg prior to an injection of pentobarbital (40 mg/kg, i.p.) was associated with a statistically significant decrease of sleep latency and prolongation of pentobarbital-induced sleeping time. Pretreatment of rats with the same alkaloid extract (150 mg/kg, i.p. for 4 days) prior to administration of pentobarbital (40 mg/kg, i.p.) caused not only significant reduction of the levels of microsomal proteins, total cytochrome P450 enzymes and a decrease of aminopyrin-N-demethylation and 3,4-benz(a)pyrene hydroxylation but also changed the pattern of cytochrome P450. It is concluded that the CAF isolated from H. apiculata can potentiate the CNS depressant effect of pentobarbital due to alteration of barbiturate metabolism through inhibition, mainly, of cytochrome P450-dependent enzymes.