Vasomotor responses of newly developed coronary collateral vessels

Well-developed coronary collateral vessels contain an abundant muscular media and can undergo active vasomotion. However, early after coronary occlusion, coronary collateral vessels are thin walled with little smooth muscle, suggesting that vasomotor capability might be limited. Consequently, this study determined whether newly developed coronary collateral vessels have active vasomotor activity and whether endothelial function in these newly developed vessels is impaired. Retrograde blood flow was measured as an index of coronary collateral blood flow ~2 wk after embolic occlusion of the anterior descending coronary artery of dogs. Agonists were administered into the left main coronary artery to reach collaterals originating from the left coronary system. Baseline retrograde blood flow was 25.1 ± 2.7 ml/min and increased to 36.7 ± 3.7 ml/min after nitroglycerin (6 μg · kg^-1 · min^{- 1}, P < 0.05). Cyclooxygenase blockade with indomethacin (5 mg/kg iv) decreased retrograde collateral blood flow to 16.8 ± 2.3 ml/min (P < 0.05). Subsequent administration of acetylcholine increased retrograde flow to 29.4 ± 3.7 ml/min (P < 0.05), indicating intact endothelium-mediated vasodilation. Inhibition of nitric oxide synthase with N(G)-nitro-L-arginine further decreased coronary collateral retrograde flow to 12.0 ± 2.8 ml/min (P < 0.05) and markedly blunted the response to acetylcholine. These findings demonstrate substantial vasomotor capability even early during coronary collateral development and indicate that both nitric oxide and cyclooxygenase-dependent endothelial mechanisms are intact.