Effects of prolactin on steroidogenesis and cAMP accumulation in rat luteal cell cultures

The effects of prolactin (PRL), alone and as a modulator of human chorionic gonadotropin (hCG) action, on steroidogenesis and cAMP accumulation in rat luteal cell cultures were examined. Cultured rat luteal cells were prepared from immature rats primed with pregnant mare serum gonadotropin and hCG. In vitro treatment was performed with 0.1 and 0.2 IU/ml hCG and 1-100 ng/ml PRL. Cultures were incubated for 48 h for evaluation of progesterone (P4) secretion and for 1 h for measurement of cAMP accumulation. The same doses of hormones and incubation periods were also used in preovulatory rat granulosa cell cultures and found to cause a significant, dose-dependent inhibition in estradiol, P4 and cAMP accumulation. In luteal cell cultures, on the other hand, P4 secretion was significantly elevated, in a dose-dependent manner, by PRL. Moreover, identical doses of PRL caused a significant, dose-dependent stimulation of cAMP accumulation. Basal levels of P4 were also significantly elevated by PRL alone, but no such stimulation by PRL was detected in basal levels of cAMP. Addition of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, increased the stimulation of P4 and cAMP by hCG + PRL in a manner dependent on PRL concentrations. The overall data therefore demonstrate divergent effects of PRL on cAMP accumulation and steroidogenesis in the ovary: inhibitory in the preovulatory and stimulatory in the postovulatory state. Moreover, these findings suggest a possible common mechanism linking the effects of PRL before and after ovulation: inhibition of cAMP accumulation via enhanced breakdown of the nucleotide.