Effects of 17 beta-estradiol, synthetic estrogens, and antiestrogens on prolactin secretion, nuclear translocation of pituitary estrogen receptor and on progesterone receptor levels in rat pituitary, hypothalamus and uterus.

Estrogen-receptor and progesterone-receptor values were studied following repeated application of estrogens and/or the antiestrogen tamoxifen. Nuclear estrogen-receptor contents of the pituitary as well as serum prolactin levels and uterus weight were increased by treatment with 17 beta-estradiol and synthetic estrogens DM-EE2 (1,3 diacetoxy-17 alpha-ethinyl-7 alpha-methyl-1,3,5(10)-estratrien-17 beta-ol) and DB-EE2 (1,3 dibenzoyloxy-17 alpha-ethinyl-7 alpha-methyl-1,3,5(10)-estratrien-17 beta-ol). Tamoxifen also increased pituitary estrogen receptor values, but no stimulation of serum prolactin levels was found. Tamoxifen decreased estradiol stimulated uterus weight, but had no repressor effects on serum prolactin levels. Progesterone receptor levels were stimulated in the pituitary by repeated injection of 17 beta-estradiol, DM-EE2 and DB-EE2 and to a smaller degree by tamoxifen. The stimulation of progesterone receptor levels by estrogen was greater in the pituitary than in the hypothalamus and uterus. The present data combine to suggest differences in metabolic and/or cellular events following stimulation with estrogens of different biological activities.