Role of nitric oxide in coronary vasomotion during handgrip exercise

Endothelium-dependent modulation of coronary vasomotion during increased sympathetic tone remains unclear in normal and atherosclerotic human coronory arteries.

We evaluated the role of endothelium-derived nitric oxide in vasomotion during isometric exercise in normal subjects (n = 7) and in patients with coronary artery disease (CAD) (n = 10). Coronary blood flow and epicardial coronary artery diameter to the handgrip test were measured before and after intracoronary administration of 100 micromol/min of N(G)-monomethyl L-arginine (L-NMMA). Heart rate and aortic blood pressure increased during handgrip test. Handgrip test caused a significant dilation in the diameter of the epicardial coronary artery in normal subjects (9.9% +/- 3.9%, mean +/- SD) and in the diameter of smooth segments of patients with CAD (5% +/- 3.7%, p < 0.05 vs normal subjects). In contrast, the diameter of irregular segments in patients with CAD decreased during handgrip test (-9.8 +/- 3.9%). After L-NMMA, the epicardial coronary artery significantly increased during handgrip test compared with before L-NMMA in normal subjects. L-NMMA did not have any effect on handgrip test induced vasodilation in the smooth segments and vasoconstriction in the irregular segments in the patients with CAD. Handgrip test-induced increases in coronary blood flow did not change after L-NMMA in both groups.

Nitric oxide does not play a major role in HNG-induced vasodilation in epicardial and microcirculatory vessels in normal human coronary circulation. Although the decreased release in nitric oxide may modulate the abnormal response of the epicardial coronary artery to handgrip test, this does not explain the paradoxic constrictive response from the depressed but still dilatory response in the patients with CAD.