Influence of a novel hypophyseal factor on steroid metabolism in cultured hepatoma cells

A rat hepatoma cell line in tissue culture (HTC cells) was treated with hypophyseal extracts from adult male and female rats. Cell homogenates were then assayed for steroid metabolizing enzymes using 4 androstene 3,17 dione as substrate. The major products were the 5α reduced derivatives (5α androstane 3,17 dione, androsterone, and epiandrosterone). When the cells were grown in the presence of female hypophyseal extract the apparent activity of the 5α reductase increased markedly, whereas treatment with male hypophyseal extract was without effect. Treatment with female hypophyseal extract resulted in a marked decrease in the apparent Km for 5α reductase from 667±120 to 99±4 μM in addition to a decrease in the apparent Vmax from 67±12 to 46±2 pmol of product/min per mg of protein. A logarithmic dose response was obtained with female hypophyseal extract. Treatment of the HTC cells with purified rat hypophyseal follicle stimulating hormone, luteinizing hormone, growth hormone, thyrotropic hormone, and prolactin had only marginal effects on 5α reductase activity. Crude female hypophyseal extracts were at least 6 fold more potent than any of the standard hormone preparations and at least 250 fold more potent than male hypophyseal extracts when based on activity per mg of pituitary tissue. Chromatography of crude female hypophyseal extracts on Sephadex G 25 indicated that the factor was of high molecular weight. The identity of this activity with a hypophyseal ''feminizing'' factor is postulated.