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

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-17β resulted in a significant decrease in mean hepatic 6β-hydroxylase activity and total cytochrome P-450 content but had no effect on the 16-hydroxylation or on the reductive metabolism of androstenedione. The effect of oestradiol-17β on hepatic 6β-hydroxylase activity was as pronounced after hypophysectomy as after sham-operation indicating that these effects of oestradiol-17β are mainly direct and independent of the pituitary gland. The results indicate that hypophysial hormone(s) as well as oestradiol-17β play a role in the regulation of hepatic steroid metabolism in trout.