Substance P Dilates Epicardial Coronary Arteries and Increases Coronary Blood Flow in Humans

The effects of intracoronary infusions of substance P in conscious humans on epicardial vessel diameter and coronary sinus oxygen saturation were investigated in 13 patients who had angiographically normal coronary arteries. The dose of substance P ranged from 2.8 to 89.6 pmol/min, starting at 2.8 pmol/min and rising by doubling increments. All infusions were performed for 2-minute periods. Epicardial vessel diameter was measured by a computerized analysis system (CAAs) of the angiogram performed at the end of each infusion period. Coronary sinus oxygen saturation (CSo2) was measured continuously by a fiber-optic oximeter catheter in the coronary sinus. A reduction of arterial pressure, indicative of a systemic effect of substance P, occurred only when infusions were 44.8 pmol/min or more. At considerably smaller dosages, a dose-dependent increase in the left anterior descending artery diameter was seen with substance P; maximal dilation occurred at a dosage of 11.2 pmol/min. The percent increase in vessel diameter for this dosage was 29.4±19.8 % (mean±+SD) at the distal site of analysis and 16.7±10 % at the proximal site of analysis. CSo2 rose in a dose-dependent manner and was maximal at a dosage of 11.2 pmol/min, which caused a 14.6±7.2 % 02 rise above the preinfusion saturation of 43.5±11.1 % 02. As the heart rate-blood pressure double product showed n