Indirect effects of progesterone on the synthesis and secretion of prolactin in mammotroph-enriched cells.

To elucidate the role of steroid hormones in the synthesis and secretion of prolactin (PRL), a mammotroph-enriched cell preparation was made by centrifugal elutriation of trypsin-dispersed anterior pituitary cells from adult male rats. The mammotrophs were enriched by about 2-fold in comparison with those in the initial cell suspension. On the other hand, the ratio of enrichment of gonadotrophs, thyrotrophs and somatotrophs was less than onetenth. The separated mammotrophs were incubated in media containing 17 beta-estradiol and/or progesterone. 17 beta-estradiol increased the levels of PRL in the medium and the cells of 300% and 140%, respectively, and the content of messenger RNA (mRNA) to 193%, whereas progesterone had no such effects. Furthermore, progesterone had no influence on the 17 beta-estradiol-induced increase in the levels of PRL and the contents of PRL mRNA. These results suggest that 17 beta-estradiol regulates PRL synthesis and secretion in mammotrophs, whereas progesterone does not.