Progesterone Inhibits the Stimulatory Effect of Estrogen on the Mammotrope Proliferation in Rat Pituitary Cultures

Lee, Byung Lan; Han, Boo Kyung

Abstract

This study was performed to investigate the effect of progesterone (P) on the estrogen-induced proliferation of mammotropes in cultures of normal rat pituitary cells. Dispersed pituitary cells from male rats were cultured in Dulbecco's Modified Eagle's medium containing striped 10% fetal bovine serum for 6 days. Part of cells were treated with 10(-9) M 17beta-estradiol with or without P (10(-6) M). For the simultaneous detection of mitotic cells and mam-motropes, bromodeoxyuridine (BrdU) labeling and double immunocytochemical staining for BrdU and prolactin were performed. The ratio of BrdU-labeled cells among mammotropes (BLI) was increased by 6.3-fold after 6 day treatment with estradiol, which was partly suppressed by 2.3-fold by additional P treatment. The percentage of mammotropes among pituitary cells was increased by 1.5-fold by estradiol treatment, which was suppressed by 1.1-fold after coadminis-tration of progesterone. Thus, coadmistration of progesterone could suppress the estradiol-induced effect on the BLI and the proportion of mammotropes by 75% and 80%, respectively. In addition, apoptotic ratio of mammotropes was not changed by hormone treatment. The present data demonstrated that progesterone inhibits estradiol-induced proliferation of mammotropes, which may contribute to the decrease in the proportion of mammotrope. The indirect modulatory effect of progesterone on the estradiol-induced increase in the prolactin secretion in the rat pituitary was suggested.