Responses of atherosclerotic human coronary arteries in vivo to the endothelium-dependent vasodilator substance P.

BACKGROUND The effects of the endothelium-dependent vasodilator substance P (SP) on atherosclerotic human coronary arteries was studied. METHODS AND RESULTS [125I]-SP binding to luminal cells was shown to be preserved in the atherosclerotic epicardial coronary arteries of four patients. No binding to medial smooth muscle cells was demonstrated. Intracoronary infusions of SP were undertaken in patients with coronary artery disease. SP was infused for 2-minute periods starting at a dose of 2.8 pmol/min rising by doubling increments to 22.4 pmol/min. Analysis of the epicardial coronary artery diameter, using a computerized analysis system (CAAS) of the angiograms, was performed at the end of each infusion. Analysis of seven smooth vessel segments from seven coronary vessels, which were stenosed at more proximal sites, was performed. Significant dose-dependent dilatation was seen (p = 0.04), which was maximal at 5.6 pmol/min SP. No additional dilatation was produced with 2 mg intracoronary isosorbide dinitrate (ISDN). Two of these seven patients showed no response to SP, and only one of these appeared to sustain dilatation with ISDN (2 mg intracoronary). In a second group of six patients with discrete coronary stenoses, analysis at the site of the stenosed segments appeared to reveal dilatation in response to SP in only one instance. One other stenotic segment dilated with isosorbide dinitrate but failed to dilate with SP; the remaining four were fixed. The segment immediately proximal to the stenosis preserved a dose-dependent vasodilator response. CONCLUSIONS These findings demonstrate that the endothelium-dependent vasodilator substance P can still produce epicardial vasodilatation in vivo in the presence of coronary atherosclerosis.