In-vitro metabolism of 4-androstene-3,17-dione by hepatic microsomes from the rainbow trout (Salmo gairdnerii): effects of hypophysectomy and oestradiol-17 beta.

The metabolism of 4-androstene-3,17-dione by liver microsomes from juvenile rainbow trout, Salmo gairdnerii, was studied in vitro. Hypophysectomy of the fish significantly increased mean hepatic 17-hydroxysteroid oxidoreductase activity when compared with that from sham-operated fish but none of the other enzyme activities investigated were affected. Administration of oestradiol-17 beta resulted in a significant decrease in mean hepatic 6 beta-hydroxylase activity and total cytochrome P-450 content but had no effect on the 16-hydroxylase or on the reductive metabolism of androstenedione. The effect of oestradiol-17 beta on hepatic 6 beta-hydroxylase activity was as pronounced after hypophysectomy as after sham-operation indicating that these effects of oestradiol-17 beta are mainly direct and independent of the pituitary gland. The results indicate that hypophysial hormone(s) as well as oestradiol-17 betal play a role in the regulation of hepatic steroid metabolism in trout.