Modulation of gonadotropin-releasing hormone receptor concentration in cultured female rat pituitary cells by estradiol treatment

Abstract

Short-term (0.5-4 h) treatment of rat pituitary cells in culture with estradiol (E 2) results in a significant decrease of Gonadotropin-Releasing Hormone (GnRH) induced LH-release. We studied whether changes in the concentrations of GnRH-receptors (GnRH-R) might account for this phenomenon: pituitary cells from adult female rats were incubated for 4 or 24 h in the presence or absence of 10 −9M E 2. Then saturation curves of D-Ala 6-des-Gly 10-GnRH ethylamide binding were obtained. In addition, binding studies were carried out in cultures incubated for 0.5, 1, 2 or 4 h with or without 10 −9 M E 2 using a near saturating concentration of GnRH-analog. No changes of GnRH-R affinity occurred (4 h experiments: K a in vehicle treated cells: 0.94 ± 0.2 × 10 9 M −1, K a in E 2 treated cells: 1.06 ± 0.3 × 10 9 M −1; 24 h experiments: K a , vehicle: 0.95 ± 0.2 × 10 9 M −1, K a E 2: 0.82 ± 0.3 × 10 9 M −1). The GnRH-R concentrations, however, were significantly reduced (44 ± 3%; P < 0.001) by 4 h E 2 treatment and increased (by 68 ± 8%; P < 0.01) by 24 h of E 2 treatment. The GnRH induced LH-release in aliquots of the same cell preparations was significantly reduced after 4 h and markedly increased after 24 h of E 2 treatment. The experiments on the time-course of the reduction of d-Ala 6-GnRH-binding by E 2 treatment showed that the number of GnRH-R was significantly decreased (24 ± 1%; P < 0.05) already after 0.5 h of exposure to the estrogen. This is also the time period after which the negative E 2-effect on GnRH-induced LH-release becomes significant. These data provide first evidence that the short-term negative E 2-effect on GnRH induced LH-release by rat pituitary cells in culture could be mediated via a reduction of available GnRH-R.