Short Term Suppression of the Hormone-Stimulable Adenylyl Cyclase System in the Granulosa Cells of the Domestic Hen by Luteinizing Hormone*

Publisher Website
Google Scholar
Abstract
In the avian ovary, granulosa cells are target cells for LH. The present experiments were performed to determine if the adenylyl cyclase (AC) system is desensitized after exposure to LH. In Exp 1, hens were injected iv with 25 or 100 μg ovine LH 12 h before ovulation. At various times postinjection, hens were killed, granulosa (Gr) cells removed from the largest (F1), second largest (F2), and third largest (F3) follicles, and AC activity was measured. The progesterone released in response to 25 fig LH was also quantitated. In Exp 2, Gr cells were isolated from the F1 follicle and subjected to one of four treatments before the AC activity was measured: 1) assayed immediately, 2) maintained at 4 C for 1 h, 3) preincubated with BSA at 37 C for 1 h, or 4) preincubated with LH at 37 C for 1 h. Results (Exp 1) were similar for both doses of LH, except that 100 μg ovine LH caused a greater suppression of AC activity. The suppression of AC activity in Gr cells of F1 and F2 follicles occurred 5 min after the injection of LH; a rebound to preinjection levels was observed at 20 min. Exposure of F3 Gr cells to LH resulted in an initial increase in basal and LH-stimulable AC activity. In response to LH, peaks of progesterone were observed 10 and 40 min after the injection of LH which were negatively correlated with enzyme activity. Maintenance of Gr cells at 4 C for 1 h had no effect on basal or LH-stimulable AC activity. Preincubation of Gr cells with BSA at 37 C for 1 h did not change the basal activity but increased relative LH stimulation 8.9-fold. Exposure of cells to LH (25 μg/ml) for 1 h at 37 C resulted in a decrease in relative stimulation compared to controls. Results indicate that: 1) the AC system of the hen's Gr cells exhibits a short term suppression in response to LH, 2) the iv injection of LH elicits a bimodal response in progesterone secretion, and 3) exposure of Gr cells to LH in vitro does not result in desensitization of the LH-stimulable AC system.