The in vitro perifused rat ovary: I. Steroid secretion in response to ramp and pulsatile stimulation with luteinizing hormone and follicle stimulating hormone

Abstract

A computer-controlled perifusion apparatus has been used to investigate the effects of different patterns of hormonal stimulation on secretion of steroids by ovaries from untreated, or pregnant mare serum gonadotropin (PMSG)-pretreated, immature rats. With ovaries from untreated rats, a low rate of increasing concentration of gonadotropins (luteinizing hormone (LH) plus follicle stimulating hormone (FSH)) induced a maximum secretion of estradiol within 60 min (22.6 +/- 1.4 pg/mg/30 min). An intermediate and a high rate of increasing gonadotropin concentration stimulated maximum secretion (26.0 +/- 1.2 pg/mg/30 min) and 28.1 +/- 2.8 pg/mg/30 min), respectively) within 30 min. Peak secretion, however, was not maintained and was reduced despite continued LH/FSH pulses. Progesterone secretion increased during, and subsequent to, the decreasing estradiol output. Increasing amplitudes of LH/FSH or constant perifusion with LH/FSH did not change the profile, or the concentration of estradiol, but these measures increased progesterone release. An occasional transient increase in estradiol secretion was observed when ovaries from unstimulated rats were perifused with low LH/FSH pulse frequency. Thus, these studies support the hypothesis that in the prepubertal rat ovary, elements of pulse characteristics, such as rate of increasing LH/FSH concentration, and amplitude are important in differentially regulating steroid output. The steroid secretory pattern of ovaries from PMSG-treated prepubertal rats was different from that of untreated rats. With ovaries from PMSG-treated rats, an acute increase in secretion of progesterone, testosterone or estradiol was not observed, whether low or high rates of increasing gonadotropin concentration were used. Rather, the concentration of these steroids continued to rise following LH/FSH pulses. Thus, in contrast to the untreated ovary, the PMSG-treated ovary did not show differential regulation of steroid secretion in response to LH/FSH. In conclusion, we have shown the in vitro perifusion model to be a useful tool for studying the effects of different patterns of hormonal stimulation on ovarian steroidogenesis. In addition, differential effects of gonadotropins on steroid output were shown, depending upon prior maturation of the ovary.