Estradiol induces a shift in cultured cells that release prolactin or growth hormone.

The process by which estradiol induces an increase in the percentage of prolactin cells in the rat pituitary requires clarification. In this study the effect of estradiol treatment on growth hormone and prolactin cells in monolayer cultures of male rat pituitaries was assessed by use of reverse hemolytic plaque assays. Treatment of cultures with 17 beta-estradiol (10 nM) for 6 days elevated significantly (P less than 0.01) the percentage of all cells in culture that released prolactin without affecting the percentage of growth hormone secretors. However, by sequentially assaying single cells for growth hormone and prolactin, we found that estradiol caused a marked increase (P less than 0.01) in the proportion of individual cells that released both growth hormone and prolactin and a commensurate decrease in the proportion that released growth hormone alone. These results demonstrate that estradiol acts directly on cultures of male pituitary cells to shift the proportions of cells that released growth hormone, prolactin, or both hormones and indicate that estradiol may convert cells that release only growth hormone to those that release both growth hormone and prolactin.