Effect of nitroglycerin on myocardial collateral conductance in awake dogs

Conductance of the coronary collateral circulation during the course of two abrupt circumflex coronary occlusions was measured in awake dogs ∼ 2 wk after collateral vessels were stimulated to develop. The pressure gradient from the central aorta to the distal circumflex coronary artery was measured, and myocardial blood flow was determined by 9-μm radioactive microspheres at 30 s and 4 min after coronary occlusions. Collateral conductance was calculated as mean collateral blood flow divided by the mean aorta-coronary pressure gradient. Before nitroglycerin, collateral conductance increased in all eight dogs from 30 s to 4 min. After nitroglycerin administration, the conductance at 30 s increased from the prenitroglycerin control value to 0.014 ± 0.012 ml·min-1·g-1·mmHg-1. The mean change in conductance from 30 s to 4 min postnitroglycerin was significantly less than during prenitroglycerin. These data indicate that an increase in conductance during coronary occlusion occurs even in the immature collateral circulation. This effect presumably takes place in the arterial smooth muscle at the origin of the collateral vasculature