OBJECTIVE To examine the effects of substance P (endothelium dependent vasodilator) and glyceryl trinitrate (endothelium independent vasodilator) on epicardial coronary arteries in patients with normal coronary angiograms and patients with coronary artery disease.

DESIGN Intracoronary infusions of normal saline, the receptor mediated nitric oxide stimulant substance P (5.6 and 27.8 pmol/min each for five minutes), and glyceryl trinitrate (250 μg bolus) were given in 24 patients with coronary artery disease and stable angina, and in nine patients with normal angiograms. The diameter of proximal and distal coronary segments was measured by computerised quantitative angiography

RESULTS Proximal segments of patients with coronary artery disease dilated less than those of patients with normal angiograms in response to 27.8 pmol/min substance P (mean (SEM): 7.9 (1.3)% v15 (2.3)% respectively, p < 0.01). The proximal segments of diseased arteries also dilated less than those of “normal” arteries in response to glyceryl trinitrate (10.2 (1.6)%v 18.4 (2.9)%, respectively, p < 0.01). The responses of distal segments to substance P and glyceryl trinitrate were similar in the two patient groups. There were correlations (all p < 0.001) between the coronary diameter after substance P and after glyceryl trinitrate in normal proximal segments (r = 0.94) and normal distal segments (r = 0.64), in diseased proximal segments (r = 0.95) and diseased distal segments (r = 0.89), and for coronary stenoses (r = 0.93).

CONCLUSIONS Proximal segments of patients with coronary disease dilated less than the proximal segments of “normal” patients in response to substance P and glyceryl trinitrate. The response to substance P is substantial and closely correlated with the response to glyceryl trinitrate in both “normal” patients and those with coronary disease. This suggests that although the proximal segments of diseased coronary arteries have a reduced capacity to dilate in response to direct stimulation of smooth muscle cell relaxation, they retain much of their endothelium dependent vasodilator function.