Exercise training enhances adrenergic constriction and dilation in the rat spinotrapezius muscle.

Treadmill training increases functional vasodilation in the rat spinotrapezius muscle, although there is no acute increase in blood flow and no increase in oxidative capacity. To assess concurrent changes in vascular reactivity, we measured arterial diameters in the spinotrapezius muscle of sedentary (Sed) and treadmill-trained (Tr; 9-10 wk; terminal intensity 30 m/min, 1.5 degrees incline, for 90 min) rats during iontophoretic application of norepinephrine, epinephrine (Epi), and H+ (HCl) and during superfusion with adenosine. Terminal-feed arteries and first-order arterioles in Tr rats constricted more than those in Sed rats at the higher current doses of norepinephrine and Epi. In contrast, at low-current doses of Epi, first- and second-order arterioles dilated in Tr but not in Sed rats. The vascular responses to HCl were highly variable, but second-order arterioles of Tr rats constricted more than those of Sed rats at intermediate-current doses. There were no significant differences between Sed and Tr rats in the vascular responses to adenosine. Both adrenergic vasodilation and vasoconstriction were enhanced in the spinotrapezius muscle of Tr rats, and enhanced adrenergic vasodilation may contribute to increased functional vasodilation. These observations further demonstrate vascular adaptations in "nontrained" skeletal muscle tissues.