Coronary arterial responses to graded doses of nitroglycerin

The potential benefit from coronary dilatation induced by nitroglycerin is thought to be limited in patients with ischemia by blood pressure reduction, heart rate increase and coronary artery disease. Because recent work with other vasodilators suggests multiple vascular receptor sites with various degrees of responsiveness, coronary dilator and systemic responses to graded doses of nitroglycerin were examined in 13 patients. High resolution, 105 mm photospot film coronary angiograms, using 4.5 or 6 inch image intensification, was performed before and after administration of cumulative doses of sublingual nitroglycerin (75 to 450 μg). A calibrated optical system was used to measure coronary arterial diameter. Small doses of nitroglycerin (75 to 150 μg) increased the diameter of the left anterior descending coronary artery by 10 and 20 percent (mean), that of the left circumflex artery by 9 and 22 percent, and that of collaterally filled vessels by 18 and 28 percent, respectively (all values significantly [P < 0.01] different from measurements before nitroglycerin). No significant change in heart rate or mean aortic pressure occurred. Doses of nitroglycerin to 450 μg produced only modest additional increases in coronary arterial diameter (left anterior descending artery 9 percent, left circumflex artery and collaterally filled vessels 7 percent). Heart rate increased 5 beats/min and blood pressure decreased 11 mm Hg with 450 μg of nitroglycerin (both P < 0.01). These data suggest that dilator receptors of both large left coronary arteries and vessels filled by collateral vessels respond to very small doses of nitroglycerin without significant changes in heart rate or blood pressure.