Xenobiotic and endobiotic induction of mixed function monooxygenase in carp Cyprinus carpio

3-Methylcholanthrene (3-MC) significantly induces aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) activity in mature and juvenile Cyprinus carpio of both sexes. The degree of induction of AHH by 3-MC in mature fish is significantly lower than that in juveniles and induction in mature males is significantly higher than in mature females. Pretreatment with sex steroids (testosterone in males and estradiol in females) significantly reduces 3-MC-inducibility of AHH in both mature and juvenile fish, while gonadectomy in mature fish elevates AHH inducibility. AHH induction is slightly decreased by hydrocortisone and increased by metyrapone pretreatment in mature fish only. Gonadectomy further elevates metyrapone affected 3-MC inducibility of AHH in C. carpio.