Exercise training and responsiveness of isolated coronary arteries

Exercise is associated with release of catecholamines and vasoactive intestinal polypeptides. Recurrent exposure to catecholamines modifies the sensitivity of adrenoceptors. To test the hypothesis that exercise training may affect the sensitivity of the epicardial coronary arteries, we performed studies on isolated coronary arteries from male dogs capable of running on a treadmill. The animals were separated randomly into two groups: sedentary and exercise training. After 11 wk, rings of left circumflex and left anterior descending coronary arteries were studied in vitro. Contractions to α₁- adrenergic agonists (norepinephrine and phenylephrine) were not affected by exercise training. During contractions with prostaglandin F(2α), endothelium-dependent relaxations to α₂-adrenergic agonists (norepinephrine and UK 14304) were not reduced significantly by exercise training. The concentration-relaxation curves to β-adrenergic agonists (norepinephrine, isoproterenol, and epinephrine) were shifted to the right after training. The concentration-response curves to vasoactive intestinal polypeptide, but not that to substance P, were shifted to the right in rings with endothelium from exercise-trained animals. These findings demonstrate a decrease in responsiveness of canine vascular smooth muscle to β-adrenergic agonists and to vasoactive intestinal polypeptide after exercise training.