Endothelium-dependent vasodilation in well-developed coronary collateral vessels

We examined endothelium-dependent vasodilator responses in well-developed coronary collateral vessels. Collateral vessels and size-matched normal epicardial coronary arteries were isolated from canine hearts 6 months after a hollow plug had been introduced into the left anterior descending coronary artery (LAD) to stimulate collateral vessel growth. Vessel segments were isolated and studied in organ chambers. After preconstriction with prostaglandin F2 alpha, (PGF2 alpha) responses to the endothelium-dependent vasodilators, acetylcholine (ACh), substance P, and bradykinin (BK), as well as the endothelium-independent vasodilator nitroglycerin (NTG), were measured. The maximum relaxation to ACh was greater in collateral vessels (129 +/- 3.6% of the preconstricted tension) than in normal vessels (110 +/- 6.2%, p < 0.001), although the EC50 value for ACh was not significantly different between collateral and normal vessels. Collateral vessels demonstrated sensitivity to BK similar to that of normal vessels, but the maximal vasodilation achieved was greater in collaterals (138 +/- 4.6% of preconstricted tension) than in normal vessels (108 +/- 5.0%, p < 0.05). Both substance P and NTG produced dose-related relaxation that was similar in collateral vessels and normal arteries. These findings demonstrate that endothelium-dependent relaxation is intact in well-developed coronary collateral vessels.