Biphasic effect of nitroglycerin on coronary hemodynamics in normal subjects

Coronary blood flow responses to nitroglycerin (NTG) in patients have been reported to be extremely variable. In dogs, NTG has a striking biphasic effect on coronary hemodynamics, consisting of a brisk increase followed by a decrease in coronary flow. To determine the effect of the drug on the coronary circulation in normal humans, NTG was injected I.C. (50 and 300 mcg) in 11 normals, and its effects on coronary flow velocity were compared to those of I. C. papaverine (6, 8, 10, and 12 mg) and saline (0.5 and 3.0 ml). Coronary flow velocity was measured using a 3F coronary Doppler catheter. The effect of each drug on coronary blood flow was analyzed in terms of both magnitude and duration (s) of the transient vasodilatory response following administration. Changes in coronary flow velocity (expressed as peak/resting velocity ratio) after 6, 8, 10, and 12 mg papaverine were (mean +/- SEM) 2.7 +/- 0.1, 3.4 +/- 0.3, 3.7 +/- 0.2, and 3.9 +/- 0.2, respectively. Very mild changes were observed with saline (1.3 +/- 0.1 and 1.7 +/- 0.1 after 0.5 and 3.0 ml, respectively), while ratios of 2.4 +/- 0.2 and 3.1 +/- 0.3 were obtained after NTG 50 and 300 mcg, respectively. The effect of 300 mcg NTG was significantly greater (p less than 0.01) than that of saline, 6 mg papaverine and 50 mcg NTG, lower than that of 12 mg papaverine and not significantly different from that of 8 and 10 mg papaverine. In terms of duration, the effect of 300 mcg NTG on coronary flow velocity was more prolonged than that of saline and 50 mcg NTG, and shorter than that of 6 to 12 mg papaverine.(ABSTRACT TRUNCATED AT 250 WORDS)