Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a novel neuropeptide with considerable homology to vasoactive intestinal peptide (VIP) and GH-releasing hormone (GHRH). Because we have shown previously that VIP and GHRH stimulate steroidogenesis in cultured rat granulosa cells independently of FSH, the present studies evaluated whether PACAP also stimulates steroidogenesis and compared its effects to those of VIP and GHRH. Granulosa cells cultured for 2 days with PACAP-27, VIP, or GHRH (10(-9)-10(-6) M) showed dose-dependent increases in the accumulation of progesterone, 20 alpha-dihydroprogesterone, and estrogen. The rank order of potency for the three peptides was PACAP >> VIP > GHRH. PACAP also increased cAMP accumulation and was again more potent than VIP. In addition, all three peptides synergistically augmented FSH-stimulated progesterone and 20 alpha-dihydroprogesterone accumulation with the same rank order of potency as above; however, only the highest dose of each peptide augmented estrogen accumulation. Further studies examined the effects of various androgens on these responses. PACAP-stimulated progesterone accumulation was minimal in the absence of androstenedione, but increased up to 40-fold in its presence. Other synthetic and naturally occurring androgens produced similar increases with a rank order of potency of R1881 > testosterone = androstenedione > dihydrotestosterone. Analysis of cAMP levels indicated that by 1 h after treatment with PACAP, cAMP levels within the cells increased by 4-fold, and this response was unaltered in the presence of androstenedione; however, by 48 h, cAMP levels had markedly declined, and this response was attenuated by androstenedione. These results demonstrate that PACAP stimulates steroidogenesis and cAMP accumulation in cultured rat granulosa cells, and it is more potent than its two homologs, VIP and GHRH. Because PACAP has been shown to be present within the ovary, these data indicate that this peptide may play a role in modulating ovarian steroidogenic activity.
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