The in vitro perifused rat ovary: V. The significance of the follicle stimulating hormone and luteinizing hormone ratio on steroid release.

In these studies, an in vitro perifusion model was used to compare stimulation of ovarian tissue with either human menopausal gonadotropin (hMG), which is an equal mixture of luteinizing hormone (LH) and follicle stimulating hormone (FSH), or with hMG plus added human FSH. Eight-hour perifusion studies were conducted on either whole, or dissected clusters of follicles from pregnant mare serum gonadotropin (PMSG)-treated rats. In the two groups, similar stimulatory protocols were used, consisting of a ramp stimulation over 60 min with either hMG (0-8 mIU/ml) or hMG plus FSH (0-8 mIU/ml hMG + 0-8 mIU/ml FSH), followed by hourly pulse stimulation with hMG (8-18 mIU/ml) or hMG plus FSH (8-18 mIU/ml hMG + 8-18 mIU/ml FSH), respectively. In the whole ovaries, no differences were detected in progesterone, testosterone, or estradiol secretion. However, in the cluster of follicles, an elevated hFSH/hMG ratio resulted in a significantly higher secretion of progesterone, testosterone and estradiol (n = 8; p < 0.05) than the steroids secreted by follicles perifused with hMG alone. In conclusion, an elevated FSH: LH ratio led to greater steroidogenic responses by the perifused cluster of follicles, but not by the whole ovary.