Modulatory actions of estradiol and progesterone on phorbol ester-stimulated LH secretion from cultured rat pituitary cells.
We compared the ability of estradiol and progesterone to modulate gonadotropin-releasing hormone (GnRH) and protein kinase C (PKC)-mediated luteinizing hormone (LH) secretion. Long-term (48 h) treatment of rat pituitary cells with 1 nM estradiol enhanced GnRH and phorbol ester (TPA)-stimulated LH secretion. This positive effect was facilitated by additional short-term (4 h) treatment with progesterone (100 nM). However, long-term progesterone treatment, which inhibited GnRH-stimulated LH secretion, did not influence TPA-stimulated gonadotropin release. These steroid actions occurred without an effect on the total amount of LH in the cell cultures (total LH = LH secreted + LH remaining in the cell) and neither the secretagogues nor the steroids altered total LH. Since GnRH or TPA-induced LH secretion depends on Ca2+ influx into the gonadotroph, we also analyzed the effects of estradiol and progesterone under physiological extracellular Ca2+ concentrations and in the absence of extracellular Ca2+. The steroids were able to influence GnRH or TPA-induced LH secretion under both conditions. However, when TPA was used as stimulus in Ca(2+)-deficient medium the relative changes induced by estradiol and progesterone were more pronounced, possibly indicating that the extracellular Ca(2+)-independent component of PKC-mediated LH secretion is more important for the regulation of the steroid effects. It is concluded that estradiol and progesterone might mediate their modulatory actions on GnRH-stimulated LH secretion via an influence on PKC. This effect can occur independently from de novo synthesis of LH and Ca2+ influx into gonadotrophs.
Ortmann
O
O
Department of Obstetrics and Gynecology, Philipps-University Marburg, Germany.
Tilse
B
B
Emons
G
G
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology*; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium