Feminization of hepatic S metabolism in male rats with a transplanted (MtT/F₄)

After transplantation of MIT/F₄ pituitary tumor cells to male rats of the Fisher strain, the masculine type of hepatic steroid metabolism was changed into a feminine pattern of enzyme activities. Liver metabolism of steroid hormones in female rats was relatively unaffected following transplantation of pituitary tumor cells. Furthermore, extract from MIT/F₄ tumors and "autonomous" pituitary tissue increased the 5α-reductase activity of hepatoma cells in the culture (HTC cells) at subsaturation concentrations of the substrate 4-androstene-3, 17-dione by decreasing the apparent K_m of the enzyme. It is concluded that the pituitary tumor (in accord with the secretion from an "autonomous" pituitary gland) secretes "feminotropin," a novel hypophyseal principle that probably is an important regulator of hepatic steroid metabolism. It is suggested that pituitary tumor tissue of the MtT/F₄ type could be used as source of feminotropin in purification studies.