1. 1. p,p′-DDE, phenobarbital, dieldrin heptachlor, chlordane and toxaphene induced rat liver microsomes exhibited increased formation of the 4,5-dihydrodiol, 3,6-quinone, 9- and 3-hydroxy-metabolites of benzo[a]pyrene and the latter three compounds also induced an increase in the rate of formation of the 9,10-dihydrodiol metabolite. Lindane was inactive as an inducer of benzo[a]pyrene hydroxylase. 2. 2. With the exception of lindane, all the organochlorine pesticides and PB induced testosterone 16α-and 16β-hydroxylases; in contrast lindane induced testosterone 6α-, 7α- and 6β-hydroxylases and PB also induced testosterone 15β-hydroxylase and androstenedione formation. 3. 3. Using a battery of monooxygenase enzyme assays it was evident that there were significant differences between PB and several organochlorine pesticides as inducers of rat hepatic cytochrome P-450-dependent monooxygenases.
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