Induction of hepatic P450s in rat by essential wood and leaf oils.

1. The effects of essential oils extracted from the wood and leaves of Chamaecyparis obtusa, Cryptomeria japonica and Thujopsis dolabrata on P450s in the hepatic microsomes of the male rat have been investigated. 2. Essential oils did not affect the content of total P450s measured photometrically. However, some metabolic activities and the levels of some forms of P450, including 2B1, were significantly increased, indicating their induction by essential oils. 3. The effects of components derived from essential oils (alpha-pinene, 1,8-cineole, cadinene and borneol) on P450s in rat hepatic microsomes were investigated. The activities of testosterone 2 beta-, 6 beta-, 16 alpha- and 16 beta-hydroxylation and the levels of P4502B1 and 3A2 were increased by 1,8-cineole and cadinene. The induction of P450s by essential oils is thought to be caused by cadinene, a major component. The P450 isoform induced by cadinene is similar to that induced by phenobarbital. However, the magnitude of induction by cadinene was less than that by phenobarbital at the dose levels studied. 4. P4502B1 and 3A2 were induced by essential oils in the perivenous area in the hepatic lobe.