Ischemia-induced coronary collateral growth is dependent on vascular endothelial growth factor and nitric oxide

Background-We hypothesized that ischemia-induced expression of vascular end othelial growth factor (VEGF) and the production of NO stimulate coronary c ollateral growth. Methods and Results-To test this hypothesis, we measured coronary collatera l blood flow and VEGF expression in myocardial interstitial fluid in a cani ne model of repetitive myocardial ischemia under control conditions and dur ing antagonism of NO synthase. Collateralization was induced by multiple (1 /h; 8/d), brief (2 minutes) occlusions of the left anterior descending coro nary artery for 21 days. In controls, collateral blood flow (microspheres) progressively increased to 89+/-9 mL.min(-1).100 g(-1) on day 21, which was equivalent to perfusion in the normal zone. Reactive hyperemic responses ( a measure of the severity of ischemia) decreased as collateral blood flow i ncreased. In N-G-nitro-L-arginine methyl ester (L-NAME)- and L-NAME+nifedip ine-treated dogs, to block the production of NO and control hypertension, r espectively, collateral blood flow did not increase and reactive hyperemia was robust throughout the occlusion protocol (P<0.01 versus control). VEGF expression (Western analyses of VEGF(164) in myocardial interstitial fluid) in controls peaked at day 3 of the repetitive occlusions but waned thereaf ter. In sham-operated dogs (instrumentation but no occlusions), expression of VEGF was low during the entire protocol. In contrast, VEGF expression wa s elevated throughout the 21 days of repetitive occlusions after L-NAME. Re verse transcriptase-polymerase chain reaction analyses revealed that the pr edominant splice variant expressed was VEGF(164). Conclusions-NO is an important regulator of coronary collateral growth, and the expression of VEGF is induced by ischemia. Furthermore, the induction of coronary collateralization by VEGF appears to require the production of NO.