The in vitro perifused rat ovary: IV. Modulation of ovarian steroid secretion by insulin

Insulin has been implicated as a regulatory factor in ovarian steroidogenesis. To assess this issue, we examined the role of insulin on steroid secretion by whole ovaries from pregnant mare serum gonadotropin (PMSG)-pretreated rats, using an in vitro perifusion ovarian model. Three concentrations of insulin were perifused in the absence and presence of gonadotropin pulse-stimulation. Bioactive insulin concentrations after perifusion of ovarian tissue were 4, 40 and 400 mIU/ml. In the absence of gonadotropin-pulse stimulation, acute perifusion with insulin had no effect on ovarian steroid secretion. During stimulation with luteinizing hormone (LH) plus follicle stimulating hormone (FSH), insulin significantly decreased the secretion of testosterone and estradiol but increased the output of progesterone. This effect was only evident after 180 min perifusion and with the highest concentration of insulin. We conclude that acute elevation of insulin concentration has no effect on basal ovarian secretion of progesterone, testosterone, or estradiol in gonadotropin-pretreated rats. However, insulin has a moderate effect on steroid secretion in ovaries exposed to LH/FSH pulsatile stimulation, resulting in a decrease in estradiol and testosterone release, and stimulation of progesterone secretion.