Androgenic regulation of hepatic metabolism of 4-androstene-3,17-dione in the rainbow trout, Salmo gairdnerII.

The metabolism of 4-androstene-3,17-dione by liver microsomes from the juvenile rainbow trout, Salmo gairdnerii, was studied in vitro. Administration of testosterone, 11 -oxotestosterone, dihydrotestosterone or 17 alpha-methyltestosterone to juvenile fish significantly increased mean hepatic 17-hydroxysteroid oxidoreductase (17-HSOR) activity. Androgen treatment tended to increase the total cytochrome P-450 content significantly in liver microsomes from 11-oxotestosterone-treated fish. On the other hand, androgen treatment decreased mean hepatic 6 beta-hydroxylase activity but did not affect 16-hydroxylase or 5 alpha-reductase activity. The suppressive effect of simultaneous administration of testosterone and oestradiol-17 beta on 6 beta-hydroxylase activity was more pronounced than when these steroids were administered separately. Furthermore, oestradiol-17 beta diminished the effect of testosterone on 17-HSOR activity. Testosterone treatment of hypophysectomized fish caused a significant increase in 17-HSOR activity when compared with activity in untreated hypophysectomized fish, indicating that this effect of testosterone is mainly direct and independent of the pituitary gland. The results indicate that androgens as well as oestradiol-17 beta play a role in the control of sexual differences in hepatic steroid metabolism in trout.