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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 17α-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 6β-hydroxylase activity but did not affect 16-hydroxylase or 5α-reductase activity. The suppressive effect of simultaneous administration of testosterone and oestradiol-17β on 6β-hydroxylase activity was more pronounced than when these steroids were administered separately. Furthermore, oestradiol-17β 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-17β play a role in the control of sexual differences in hepatic steroid metabolism in trout.
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The effects of oestradiol-17β 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-17β caused significant decrease in the liver microsomal metabolism of BP, PNA and EM while hypophysectomy had no effect. The suppressive effect of oestradiol-17β on the mixed function oxidases was as pronounced in hypophysectomized as in sham-operated fish, indicating that this effect of oestradiol-17β is mainly direct and independent of the pituitary gland. Administration of oestradiol-17β caused a significant increase in the apparent K m values of the PNA-O-demethylase whereas no alteration was seen in the apparent V max values of the enzyme. The results indicate that oestradiol-17β may play a role in the regulation of hepatic mixed function oxidases in rainbow trout.
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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.
