Effect of pituitary adenylate cyclase-activating polypeptide (PACAP) on progestin biosynthesis in cultured granulosa cells from rat ovary and expression of mRNA encoding PACAP type IA receptor.

The purpose of this study was to detect the presence of mRNA encoding pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptor in granulosa cells from rat ovary and to examine the effect of PACAP on progestin biosynthesis. mRNA was isolated from granulosa cells from the ovaries of immature rats treated with pregnant mares' serum gonadotrophin. The technique of reverse transcription and polymerase chain reaction with primers specific to PACAP type I receptor were used to demonstrate the expression of mRNA encoding PACAP type IA receptor in these cells. Granulosa cells were also cultured in the absence or presence of 100 ng LH ml-1 with various doses of PACAP-38 (10, 100 and 1000 ng ml-1). At the end of the incubation period, the incubation media were collected and concentrations of progesterone, 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-P) and cAMP were measured. Increasing concentrations of PACAP-38 significantly stimulated the production of progestins (progesterone and 20 alpha-OH-P) and cAMP accumulation in a dose-dependent manner (P < 0.01; ANOVA). This effect was observed in media cultured for 24 and 48 h in both basal and LH-stimulated states. PACAP-38 did not significantly affect the ratio of progesterone: 20 alpha-OH-P produced by granulosa cells cultured for 24 h in the LH-stimulated state. However, at 1000 ng ml-1, PACAP-38 significantly decreased the ratio of progesterone to 20 alpha-OH-P production in granulosa cells cultured for 48 h (P < 0.01). These results suggest that granulosa cells from rat ovary express mRNA encoding PACAP type IA receptor and that PACAP may regulate granulosa cell differentiation and play an important role in the reproductive process.