Effects of estradiol on basal and luteinizing hormone releasing hormone (LHRH) - induced release of luteinizing hormone (LH) from bovine pituitary cells in culture

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 hr (chronic) before LHRH was added. Estradiol exposure for 2 hr did not affect basal LH release. In contrast, basal LH release by pituitary cells incubated for 26 hr with 5, 50 and 500 ng E2/ml media averaged 26, 37 and 33 ng/ml, greater (P<0.005) than the 6 ng/ml average for controls. LH release increased linearly (P<0.1) with log dose of LHRH when 0, 5, or 50 ng/ml E2 was added to the media beginning 2 or 26 hr 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 (P<0.01) LHRH-induced LH release. LH content in cells not exposed to E2 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. The authors 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.