Mechanism of SNAP potentiating antiproliferative effect of calcitonin gene-related peptide in cultured vascular smooth muscle cells

We previously showed that CGRP inhibits cell proliferation which correlates with an elevation of cAMP levels in rabbit aortic vascular smooth muscle c ells (VSMCS). The present study determined the effects of S-nitroso-N-acety lpenicillamine (SNAP, a nitric oxide donor) on CGRP-induced antiproliferati ve effects and cellular mechanism in cultured rabbit aortic VSMCs. The cell s (in fifth-sixth passage) were exposed to 2.5% fetal bovine serum for 24 h in the presence or absence of SNAP, hCGRP or both. H-3-thymidine incorpora tion was used to measure DNA synthesis. The results showed that SNAP (60-10 0 mu M) significantly inhibited the proliferation and elevated cGMP levels in cultured rabbit aortic VSMCs. In combination, however. SNAP (30 mu M) po tentiated hCGRP (10-100 nM)-induced antiproliferation. SNAP (30 mu M) and h CGRP (10-100 nM) or forskolin (10 mu M), an activator of adenylate cyclase, caused more than additive cAMP elevations, but not cGMP elevations, in the se cells. Quazinone, an inhibitor of cCMP-inhibited-phosphodiesterase (cGI- PDE. PDE3), or SNAP plus quazinone caused a similar potentiation as SNAP of the hCGRP-induced elevations of cAMP levels. The data indicate that SNAP-i nduced potentiation of CGRP's effects likely involves inhibition of cGI-PDE , thus allowing enhanced accumulation of cAMP that mediates the antiprolife rative effects of hCGRP in cultured rabbit aortic VSMCs. (C) 1999 Academic Press.