Effects of Estradiol on Basal and Luteinizing Hormone Releasing Hormone (LHRH)-Induced Release of Luteinizing Hormone (LH) from Bovine Pituitary Cells in Culture1

Abstract

The effect of estradiol-17β (E₂) in regulation of basal and luteinizing hormone releasing hormone (LHRH) mediated release of LH was studied. Bovine anterior pituitaries were dispersed and ∼5 x 10⁵ cells in 1 ml medium were dispensed to each well of multiwell culture plates. LHRH at concentrations of 0.01, 0.1, 1 and 10 ng/ml increased LH release 3, 23, 94 and 183%, relative to controls without LHRH. In addition, experiments were conducted as 4 x 5 factorials where concentrations of E₂ (0, 5, 50 or 500 ng/ml) and concentration of LHRH (0, 0.1, 1, 10 and 100 ng/ml) were main effects. Estradiol was present in media beginning 2 h (acute) or 26 h (chronic) before LHRH was added. Estradiol exposure for 2 h did not affect basal LH release. In contrast, basal LH release by pituitary cells incubated for 26 h with 5, 50 and 500 ng E₂/ml media averaged 26, 37 and 33 ng/ml, greater (P2 was added to the media beginning 2 or 26 h before LHRH. Dose response slopes were 0.75, 1.40 and 2.12 (acute) and 1.5, 13.4 and 10.5 (chronic), respectively. Acute, but not chronic exposure of pituitary cells to 500 ng/ml E₂ inhibited (P2 was 854 ng. LH content was increased 201, 360 and 542% relative to untreated controls by chronic exposure of cells to 5, 50 or 500 ng E₂/ml media. We conclude that chronic exposure of bovine pituitary cells to E₂ increased basal LH release and synthesis. In addition, acute exposure of bovine pituitary cells to 5 or 50 ng/ml E₂ or chronic exposure to 5, 50 or 500 ng/ml E₂ increased sensitivity of bovine pituitary cells to LHRH.