Estradiol modulation of GNRH-stimulated LH release in rat anterior pituitary cells: involvement of dihydropyridine-sensitive calcium channels.

Although enhancement of GnRH-stimulated luteinizing hormone (LH) release by estradiol (E2) has been established, it is not known at what stages of the process of transduction E2 acts. We investigated the release of LH in response to GnRH and to Bay K 8644, an activator of L-type calcium channels, in a culture of pituitary cells obtained from ovariectomized females, these cells having being treated or not with E2 (OVX + E2 and OVX). We studied the effects of D600, an antagonist of T- and L-type calcium channels, and PN 200-110, an antagonist of L-type calcium channels. The effects of the latter were studied in protein kinase C-depleted cells in order to investigate the possible phosphorylation of these channels. D600 caused a decrease in GnRH-stimulated LH release in OVX and OVX + E2 cells. However, this decrease was greater in OVX + E2 cells, suggesting that at least one type of calcium channels may be involved as a result of treatment with E2. We confirmed the involvement of L-type calcium channels in the action of GnRH since the GnRH-stimulated LH release was enhanced in the presence of Bay K 8644 in OVX cells. Bay K 8644 alone increased basal LH in a dose-dependent manner only in OVX + E2 cells. PN 200-110 induced a decrease of GnRH-stimulated LH release only in OVX + E2 cells. These results suggest that L-type calcium channels are activated in E2-treated cells. The dose-dependent decrease caused by PN 200-110 in OVX + E2 cells disappeared in the OVX + E2 PKC-depleted cells. This result was confirmed with Bay K 8644 and suggests a phosphorylation of dihydropyridine-sensitive calcium channels by protein kinase C.