Stimulation of ovarian adenylyl cyclase activity by gonadotrophins during the natural and gonadotrophin-induced cycles in the hamster.

In this study we utilized the hamster ovary as a model to investigate the effects of ovulation induction with gonadotrophin on the activation of the signal transducer effector system, adenylyl cyclase (AC). For this purpose, we prepared membrane particles from the ovary and analysed both gonadotrophin-sensitive AC and non-receptor-mediated activation during a cycle in which ovulation and luteinization were achieved by pregnant mare's serum gonadotrophin (PMSG)/human chorionic gonadotrophin (HCG) administration. Results were directly compared with AC activation in similarly prepared membranes obtained at different stages of the natural unstimulated cycle. AC activity was quantified by the direct conversion of ATP substrate into cyclic adenosine monophosphate (cAMP). Measurements of ovarian weights, serum oestradiol and progesterone concentrations provided a solid base from which to evaluate the functional status of the ovary at each time period during the natural and stimulated cycles. We found that ovarian membranes contain functional components of the AC system and demonstrated that AC is highly dependent on hormonal changes and the functional state of the ovary. Thus, during the natural cycle, ovarian AC showed relatively constant responsiveness to follicle-stimulating hormone (FSH) throughout the cycle, whereas responsiveness to luteinizing hormone (LH)/HCG reached its peak during the luteal phase. On the other hand, during the stimulated cycle, sensitivity to FSH and LH/HCG varied considerably, being absent during the peri-ovulatory period. AC responsiveness to gonadotrophins was only regained 48 h after ovulation. Also during the peri-ovulatory period of the gonadotrophin-induced cycle, stimulation of ovarian AC with non-hormonal activators declines.(ABSTRACT TRUNCATED AT 250 WORDS)