Proximal coronary vasomotor reactivity after exercise training in dogs

The effects of exercise on large coronary vasoreactivity were determined in eight dogs trained by treadmill running for 8 weeks. Six nontrained dogs comprised the control group. The trained group showed a significant reduction in heart rate during graded submaximal exercise testing when compared with the controls, and resting plasma levels of norepinephrine (nontrained group, 331 +/- 99 pg/ml; trained group, 142 +/- 30 pg/ml; p less than .05) and epinephrine (nontrained, 424 +/- 105; trained, 258 +/- 45 pg/ml; p less than .05) were reduced significantly in the trained group. Epicardial coronary responses to intracoronary infusion of serotonin and phenylephrine were evaluated by quantitative coronary angiography, and myocardial blood flow was measured with 15 microns radioactive microspheres. Left ventricular/body weight ratio was similar in the trained (4.81 +/- 0.24 g/kg) and nontrained groups (4.79 +/- 0.17), and no differences were noted in resting myocardial oxygen consumption or coronary arteriovenous oxygen difference. The constriction of the proximal left anterior descending artery (LAD) in response to serotonin infusion was not different in the two groups, but the LAD and circumflex artery constrictor responses to phenylephrine were attenuated in the trained when compared with the nontrained dogs. The data indicate that endurance exercise diminishes the large epicardial coronary vasoconstrictor response to alpha-adrenergic stimulation, but not to serotonin. The blunted constrictor response in the trained animals suggests that exercise may be useful in reducing epicardial coronary vasoconstriction, which is thought to be important in some patients with coronary artery disease.