The metabolism of 4-[4- 14C]androstene-3,17-dione was studied in the microsomal fraction of rat livers after continuous administration of human GH (hGH) in Alzet osomotic minipumps under varying conditions. hGH caused a complete feminization of hepatic steroid metabolism (i.e. increased the 5α-reductase and decreased the 6β- and 16α-hydroxylase activities) in normal male rats when infused at a rate of 5 μg/h for 7 days. Hypophysectomy and castration or adrenalectomy and thyroidectomy of male rats did not reduce the feminizing capacity of hGH, indicating that the adrenals and the thyroid gland are not involved in the mediation of the feminizing effect of hGH. The same dose (5 μg/h for 7 days) of hGH was also able to refeminize the liver steroid metabolism in hypophysectomized-ovariectomized female rats. The effect of the homologous hormones, rat PRL and rat GH on hepatic steroid metabolism was also investigated. Either hormone was infused at a rate of 10 μg/h for 7 days, a dose which was sufficient to increase the serum level of the hormone in hypophysectomized animals. No feminizing effect was seen after the administration of rat PRL, whereas rat GH caused a partial feminization of hepatic steroid metabolism in hypophysectomized male animals. It is concluded that GH or a hormone related to GH is involved in sexual differentiation of liver steroid metabolism.
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