Antimitogenic actions of organic nitrates are potentiated by sildenafil and mediated via activation of protein kinase A

Migration and proliferation of vascular smooth muscle cells (SMC) in respon se to platelet-derived growth factor (PDGF) and other mitogens play an impo rtant role in restenosis after coronary angioplasty. Elevation of both cAMP and cGMP has been shown to inhibit SMC mitogenesis. The aim of this study was to examine the antimitogenic actions of organic nitrates and sildenafil and to clarify the role of cyclic nucleotide-dependent protein kinases (PK A, PKG) in this action. Organic nitrates [glycerol trinitrate (GTN), isosor bide 5'-mononitrate (ISMN), pentaerythrityl-tetranitrate (PETN)] and the PD E5 inhibitor sildenafil reduced PDGF-induced DNA synthesis, measured by (H- 3] thymidine incorporation. GTN, ISMN, and PETN acted synergistically with sildenafil (1 muM) on inhibition of PDGF-induced DNA synthesis, increase of intracellular cyclic nucleotides, and vasodilator-stimulated phosphoprotei n phosphorylation. The highly selective PKA inhibitor PKI abolished these a ctions of sildenafil and organic nitrates, whereas the PKG inhibitors KT582 3 and (Rp)-8-pCPT-cGMPS had no effect. In addition, selective activation of PKG without inhibition of PDE3 by the cGMP analog 8-pCPT-cGMP (100 muM) ha d no antimitogenic effect. The data suggest that 1) organic nitrates and si ldenafil exert antimitogenic actions by activation of PKA via inhibition of PDE3, but not by activation of PKG and 2) that antimitogenic effects of or ganic nitrates are potentiated by sildenafil at therapeutic plasma levels.