The effect of intravenous nitroglycerin on coronary blood flow and infarct size during myocardial infarction in conscious dogs.

Nitroglycerin (TNG), based on electrocardiographic evidence, has been shown to reduce myocardial ischemia, but its effect on morphometrically and enzymatically estimated infarct size has not been defined. Accordingly, coronary occlusion was produced in 50 conscious dogs without LV failure. Twenty-five received TNG (200-300 micrograms/min i.v. for 8 h) and the results compared with those in 25 untreated dogs. Coronary blood flow was measured with 141Ce, 85Sr, and 95Nb (9 microns) after occlusion before TNG, 30 min after TNG, and again at 8 h. Mean blood pressure decreased from 103 to 84 mmHg with TNG vs. 99 to 94 mmHg in controls (p < 0.02). Average heart rates were similar [135 +/- 26 vs. 120 +/- 33 beats/min (SD)]. TNG Did not increase total transmural coronary flow in any region but increased subendocardial flow in the central ischemic areas by 45% (0.09 ml/min/g vs. 0.13 ml/min/g). Animals were sacrificed after 24 h. Infarct size estimated morphometrically (25 +/- 1.5 vs. 26 +/- 1.5 of LV weight) and from myocardial CK depletion (23 +/- 2 vs. 23 +/- 2) was similar for the two groups. Thus, despite increased subendocardial flow, prolonged i.v. TNG did not decrease infarct size even though a difference of 15% would have been detected with this sample size. TNG May relieve coronary spasm but does not appear to be beneficial with sustained coronary occlusion.