CGRP ENHANCES INDUCTION OF NO SYNTHASE IN VASCULAR SMOOTH-MUSCLE CELLS VIA A CAMP-DEPENDENT MECHANISM

Experiments were designed to examine whether calcitonin gene-related p eptide (CGRP), a potent adenosine 3',5'-cyclic monophosphate (cAMP)-de pendent vasodilator, affects the production of NO evoked by interleuki n-1 beta (IL-1 beta) in cultured rat aortic smooth muscle cells (SMC). CGRP, in a concentration-dependent manner, enhanced the release of ni trite (a stable oxidation product of NO) and the formation of L-citrul line from L-arginine caused by IL-1 beta. Two cAMP-dependent vasodilat ors, forskolin and isoproterenol, and the activator of the cAMP-depend ent protein kinase, Sp-cAMPS, also enhanced the release of nitrite and the formation of L-citrulline evoked by IL-1 beta. The enhancing effe ct of isoproterenol required the presence of the vasodilator during th e induction of NO synthase (NOS). IL-1 beta-treated vascular SMC inhib ited the aggregation of indomethacin-treated platelets. Inhibition of platelet aggregation was more marked with SMC exposed to a combination of IL-1 beta and either CGRP or isoproterenol than with cells exposed to IL-1 beta alone. This inhibition was prevented by methylene blue a nd oxyhemoglobin. IL-1 beta induced the expression of inducible NOS mR NA in vascular SMC, which was enhanced by coincubation of IL-1 beta wi th either CORP, isoproterenol, or forskolin. These observations indica te that CGRP via a cAMP-dependent mechanism potentiates the IL-1 beta- induced production of NO by enhancing the expression of inducible NOS, Therefore CGRP may contribute to the substantial production of NO in the vasculature during septic shock, which accounts, at least in part, for the collapse of the vascular system.