PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE INDUCES CAMP PRODUCTION INDEPENDENTLY FROM VASOACTIVE INTESTINAL POLYPEPTIDE IN OSTEOBLAST-LIKE CELLS

Pituitary adenylate cyclase-activating polypeptide (PACAP) isolated fr om ovine hypothalamic tissue is a novel neuropeptide which stimulates adenylate cyclase in rat anterior pituitary cell cultures. In osteobla sts, the detail of intracellular signalling systems of PACAP has not y et been clarified. In this study, we investigated the effects of PACAP on cAMP accumulation, phosphoinositide hydrolysis and Ca2+ influx in osteoblast-like MC3T3-E1 cells, compared with those of vasoactive inte stinal polypeptide (VIP), which shows a considerable homology with PAC AP in the N-terminal sequence. PACAP stimulated cAMP accumulation in a dose-dependent manner in the range between 0.1 nM and 0.1 mu M in the se cells. VIP also stimulated cAMP accumulation dose-dependently betwe en 1 nM and 0.1 mu M. The effect of PACAP on cAMP accumulation (EC(50) = 3 nM) was more potent than that of VIP (EC(50) = 30 nM). The cAMP a ccumulation stimulated by a combination of PACAP (3 nM) and VIP (30 nM ) was additive. [Lys(1), Pro(2,5), Arp(3,4) Tyr(6)]-VIP, an antagonist for the VIP receptor which markedly inhibited the VIP-induced cAMP ac cumulation, had little effect on the PACAP-induced cAMP accumulation. Either PACAP or VIP had little effect on the formation of inositol pho sphates and Ca2+ influx in these cells. These results strongly suggest that PACAP stimulates cAMP production via an independent binding site from VIP in osteoblast-like MC3T3-E1 cells and that PACAP has no effe ct on the activation of protein kinase C nor the intracellular Ca2+ mo bilization in these cells.