CGRP is a well-known neuropeptide that has various protective effects on cardiovascular system. Our previous studies have shown that CGRP inhibits vascular smooth muscle cell (VSMC) proliferation in vitro. The present study aimed to explore the role of the CGRP in neointimal formation after balloon injury in the rat aortic wall and the underlying mechanism. Gene transfer of CGRP was performed with the use of intramuscular electroporation in a balloon-injured rat aorta model. Apoptosis in VSMCs was determined by electrophoresis assessment of DNA fragmentation and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay. Overexpression of the CGRP gene significantly inhibited the neointimal formation after balloon injury compared with the mock transfer, as assessed by the intima-to-media ratio 14 days after balloon injury (29.2 +/- 3.7% vs. 52.7 +/- 5.4%; n = 9-12, P < 0.05). In addition, CGRP gene expression increased the number of apoptotic cells in the neointima in vivo 14 days after balloon injury. Similarly, the addition of bioactive CGRP and the nitric oxide donor induced similar apoptosis in cultured VSMCs. The antagonist of the CGRP(1) receptor and inhibitors of cAMP-PKA and nitric oxide blocked CGRP-mediated apoptosis. Furthermore, CGRP gene transfer increased inducible nitric oxide synthase and p53 but decreased PCNA and Bcl-2 protein levels in balloon-injured rat aorta. Our data demonstrated that CGRP potently inhibited neointimal thickening in the rat aorta, at least in part through its distinct effects on apoptosis and proliferation of VSMCs both in vivo and in vitro. Therefore, delivery of the CGRP gene may have therapeutic implications in limiting vascular restenosis.