Does indomethacin attenuate the coronary vasodilatory effect of nitroglycerin?

Although previous studies have shown that indomethacin attenuates the dilative effects of nitroglycerin on human peripheral veins and canine coronary arteries, its ability to alter the influence of nitroglycerin on coronary blood flow in human beings is unknown. In 22 patients (16 men and 6 women, aged 47 ± 10 years [mean ± standard deviation]) referred for the evaluation of chest pain, heart rate, systemic arterial pressure, coronary sinus blood flow (by thermodilution) and coronary vascular resistance (mean arterial pressure/coronary sinus blood flow) were measured before and during the administration of intracoronary saline solution (n = 6, [control subjects]) or intracoronary nitroglycerin, 100 μg (n = 16). Of these 16 patients, 8 had no pretreatment and the other 8 received 50 mg of indomethacin orally, 10 and 2 to 3 hours before study. In the six control subjects, no variable changed with saline injection. In the eight patients given nitroglycerin without indomethacin pretreatment, heart rate and mean systemic arterial pressure were changed modestly (72 ± 15 to 74 ± 15 beats/min and 93 ± 9 to 87 ± 13 mm Hg, respectively, p < 0.05), coronary sinus blood flow increased by 56 ± 43% (107 ± 72 to 155 ± 78 ml/min, p < 0.001) and coronary vascular resistance decreased (1.12 ± 0.50 to 0.66 ± 0.26 mm Hg/ml per min, p = 0.004). Indomethacin did not attenuate the response to nitroglycerin (heart rate, 64 ± 12 to 64 ± 12 beats/min, p = NS; mean systemic arterial pressure, 96 ± 7 to 92 ± 6 mm Hg, p = 0.008; coronary sinus blood flow, 110 ± 22 to 198 ± 59 ml/min, p < 0.001 [average increase of 78 ± 33%] and coronary vascular resistance, 0.91 ± 0.25 to 0.51 ± 0.20 mm Hg/ml per min, p < 0.001). Thus, intracoronary nitroglycerin causes an increase in coronary sinus blood flow and a decrease in coronary vascular resistance, and this effect is not attenuated by indomethacin.