Effects of cytochrome P-450 monooxygenase inducers on mouse hepatic microsomal metabolism of testosterone and alkoxyresorufins

The effects of treatment with phenobarbital, l,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), pregnenolone-16/ga-carbonitrile (PCN), 3-methylcholanthrene (3-MC) and isosafrole on the hepatic microsomal formation of nine monohydroxy metabolites of testosterone and the O-dealkylation of the ethyl and pentyl ethers of resourfin were evaluated in adult male C57BL/6J and DBA/ 2NCR mice. In both strains, phenobarbital, TCPOBOP and PCN induced testosterone 2β-, 6β-, 15β-and 16/gb-hydroxylases up to 5-fold, while phenobarbital and TCPOBOP increased the rate of dealkylation of pentoxyresorufin by approximately 30-fold. However, phenobarbital and TCPOBOP did not exhibit identical patterns of induction for the testosterone oxidation reactions. Hepatic microsomes from C57BL/6J mice treated with TCPOBOP displayed a depression in 6α-testosterone hydroxylase activity, which was also observed in PCN-treated animals, whereas phenobarbital-treated mice exhibited an elevation in this monooxygenase activity. A dose of TCPOBOP (0.5 μmol/kg) previously demonstrated to represent an ED₅₀ for mouse aminopyrine N-demethylase activity was also found to approximate the ED₅₀ for pentoxyresonifin O-dealkylase activity in the C57BL/6J mouse. Isosafrole or 3-MC treatment had little effect on testosterone metabolism or pentoxyresorufin O-dealkylase activity in either strain, while 3-MC induced ethoxyresorufin O-deethylase activity in C57BL/6J but not DBA/2NCR mice. This study confirms that TCPOBOP is a potent cytochrome P-450 inducer which most closely resembles phenobarbital in its mode of action. However, TCPOBOP and phenobarbital do not evoke identical modulations of cytochrome P-450-dependent monooxygenases in mice.