Effects of oestradiol-17 beta and hypophysectomy on hepatic mixed function oxidases in rainbow trout

The effects of oestradiol-17 beta and/or hypophysectomy on the metabolism of benzo (a) pyrene (BP), paranitroanisole (PNA), ethylmorphine (EM) and 7-ethoxycoumarin by liver microsomes from juvenile rainbow trout, Salmo gairdnerii, were studied. Administration of oestradiol-17 beta caused significant decrease in the liver microsomal metabolism of BP, PNA and EM while hypophysectomy had no effect. The suppressive effect of oestradiol-17 beta on the mixed function oxidases was as pronounced in hypophysectomized as in sham-operated fish, indicating that this effect of oestradiol-17 beta is mainly direct and independent of the pituitary gland. Administration of oestradiol-17 beta caused a significant increase in the apparent Km values of the PNA-O-demethylase whereas no alteration was seen in the apparent Vmax values of the enzyme. The results indicate that oestradiol-17 beta may play a role in the regulation of hepatic mixed function oxidases in rainbow trout.