Chronic exercise training improves ACh-induced vasorelaxation in pulmonaryarteries of pigs

We hypothesized that exercise training would lead to enhanced endothelium-d ependent vasodilation in porcine pulmonary arteries. Pulmonary artery rings (2- to 3-mm OD) were obtained from female Yucatan miniature swine with sur gically induced coronary artery occlusion (ameroid occluder). Exercise trai ning was performed for 16 wk, and vasomotor responses were studied by using standard isometric techniques. Contractile responses to 80 mM KCl, isosmot ic KCl (10-100 mM), and norepinephrine (10(-8) to 10(-4) M) did not differ between sedentary (Sed) and exercise-trained (Ex) pigs. Relaxation was asse ssed to endothelium-dependent and endothelium-independent vasodilators afte r norepinephrine contraction. Pulmonary arteries of Ex pigs exhibited great er maximal relaxation to ACh (61.9 +/- 3.5%) than did those of Sed pigs (52 .3 +/- 3.9%; P < 0.05). Endothelium-independent relaxation to sodium nitrop russide did not differ. Inhibition of nitric oxide synthase significantly d ecreased acetylcholine-induced relaxation, with greater inhibition in arter ies from Ex pigs (P < 0.05). Inhibition of cyclooxygenase enhanced relaxati on to acetylcholine in arteries from Sed pigs. We conclude that exercise tr aining enhances endothelium-dependent (ACh-mediated) vasorelaxation in pulm onary arteries by mechanisms of increased reliance on nitric oxide and redu ced production of a prostanoid constrictor.