ROLE OF NITRIC-OXIDE IN CORONARY VASOMOTION DURING HANDGRIP EXERCISE

Background Endothelium-dependent modulation of coronary vasomotion dur ing increased sympathetic tone remains unclear in normal and atheroscl erotic human coronary arteries. Methods and Results we evaluated the r ole of endothelium-derived nitric oxide in vasomotion during isometric exercise in normal subjects (n = 7) and in patients with coronary art ery disease (CAD) (n = 10). Coronary blood flow and epicardial coronar y artery diameter to the handgrip test were measured before and after intracoronary administration of 100 mu mol/min of N-G-monomethyl L-arg inine (L-NMMA). Heart rate and aortic blood pressure increased during handgrip test. Handgrip test caused a significant dilation in the diam eter of the epicardial coronary artery in normal subjects (9.9% +/- 3. 9%, mean +/- SD) and in the diameter of smooth segments of patients wi th CAD (5% +/- 3.7%, p < 0.05 vs normal subjects). In contrast, the di ameter of irregular segments in patients with CAD decreased during han dgrip test (-9.8 +/- 3.9%). After L-NMMA, the epicardial coronary arte ry significantly increased during handgrip test compared with before L -NMMA in normal subjects. L-NMMA did not have any effect on handgrip t est induced vasodilation in the smooth segments and vasoconstriction i n the irregular segments in the patients with CAD. Handgrip test-induc ed increases in coronary blood flow did not change after L-NMMA in bot h groups. Conclusions Nitric oxide does not play a major role in HNG-i nduced vasodilation in epicardial and microcirculatory vessels in norm al human coronary circulation. Although the decreased release in nitri c oxide may modulate the abnormal response of the epicardial coronary artery to handgrip test, this does not explain the paradoxic constrict ive response from the depressed but still dilatory response in the pat ients with CAD.