Endothelial dysfunction in human intramyocardial small arteries in atherosclerosis and hypercholesterolemia.

Vascular responses of human intramyocardial small arteries were examined in vitro to assess the influence of atherosclerosis and risk factors for coronary artery disease on endothelium-dependent relaxation. Recipient hearts were obtained from patients with ischemic (n = 14) and nonischemic (n = 13) cardiomyopathy undergoing heart transplantation. Small intramyocardial coronary arteries (mean internal diameter 313 +/- 11 micrometers) were mounted on a wire myograph for measurement of morphology and isometric tension. Vasodilation was examined after preconstriction with U-46619, a thromboxane A2 analog. Endothelium-dependent relaxation to acetylcholine and bradykinin was impaired in patients with ischemic compared with nonischemic cardiomyopathy (P < 0.01 and P < 0.001, respectively). Endothelium-independent relaxation to sodium nitroprusside was preserved. Incubation with L-arginine (3 mmol/l) did not improve endothelium-dependent relaxation to acetylcholine or bradykinin. With the use of stepwise multivariate analysis, hypercholesterolemia, but no other risk factor for atherosclerosis, was independently associated with impaired endothelium-dependent relaxation to acetylcholine (r = -0.50, P = 0.05) but not to bradykinin. Endothelial dysfunction in intramyocardial small arteries may predispose patients with nonobstructive epicardial atherosclerosis and hypercholesterolemia to myocardial ischemia.