PHYSICAL CONDITIONING CAN MODULATE ENDOTHELIUM-DEPENDENT VASORELAXATION IN RABBITS

To investigate whether exercise training can modulate endothelium-depe ndent vasorelaxation, male New Zealand White rabbits were divided into either control or training groups. The training animals were trained on a treadmill with a running speed of 0.88 km/hr on a 0-degrees grade for 10-60 minutes/day, 5 days/week for 8 weeks. After exercise traini ng, the resting heart mte was lowered (p < 0.05). At the end of the ex periments, three vessel segments, i.e., the thoracic aortas, the pulmo nary arteries, and the common carotid arteries, were isolated and prec ontracted with norepinephrine. Acetylcholine-stimulated endothelium-de rived relaxing factor (EDRF) release was assessed by bioassay in the p resence Of indomethacin (10(-5) M). Basal release of EDRF was examined by the addition of hemoglobin. In addition, the relaxing responses of the thoracic aortas and pulmonary arteries to A23187, a calcium ionop hore, and to sodium nitroprusside, a direct vasodilator of vascular sm ooth muscle, were compared between control and trained groups to furth er investigate possible underlying mechanisms. The results indicated t hat after exercise training 1) both the thoracic aorta and pulmonary a rtery, but not the carotid artery, became more sensitive to acetylchol ine-induced vasorelaxation; 2) no significant differences in basal rel ease of EDRF between control and trained rabbits were observed; and 3) there were no significant differences in the vascular responses to A2 3187 or sodium nitroprusside between the two groups. Our data suggest that exercise training may enhance endothelium-dependent vasodilation to acetylcholine via the stimulated EDRF release and that this elevate d sensitivity to acetylcholine may not be caused by the alteration of the relaxing response in vascular smooth muscle.