The effect of four different clonal pituitary tumors on hepatic steroid metabolism was studied in male and female rats and this effect was related to the secretion of prolactin, LH and FSH from the tumors. Tumors derived from the cell line C811RAP caused an alteration of the steroid metabolism to a completely female pattern in male rats whereas it had little effect on metabolism in female rats. This tumor cell line was the only one which appeared to secrete prolactin according to the observed level of this hormone in host serum. Furthermore, extract from C811RAP tumor tissue increased the 5α-reductase activity in cultured HTC cells. The other cell lines tested (C29RAP, C13RAP and C311RAP) did not appear to secrete prolactin but did have general effects on the hepatic steroid metabolism of both sexes. These effects could not be interpreted as changes towards a female or a male pattern of metabolism. When extract from C13RAP or C311RAP tumor tissue was assayed in the HTC cell system, small or insignificant effects on the 5α-reductase activity were observed. In conclusion, it appears that the C811RAP pituitary tumor cell line produces a factor(s) that induces a female type of hepatic steroid metabolism in the rat. This factor does not seem to be produced by the other cell lines tested. Based on the clonal nature of the cells and the fact that the C811RAP cells also secrete prolactin, it is reasonable to suggest that the mammotrophs of the normal female pituitary are the cells that produce this factor.
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