EXERCISE TRAINING ENHANCES ADRENERGIC CONSTRICTION AND DILATION IN THE RAT SPINOTRAPEZIUS MUSCLE

Treadmill training increases functional vasodilation in the rat spinot rapezius muscle, although there is no acute increase in blood flow and no increase in oxidative capacity. To assess concurrent changes in va scular reactivity, we measured arterial diameters in the spinotrapeziu s muscle of sedentary (Sed) and treadmill-trained (Tr; 9-10 wk; termin al intensity 30 m/min, 1.5 degrees incline, for 90 min) rats during io ntophoretic 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 contras t, at low-current doses of Epi, first- and second-order arterioles dil ated in Tr but not in Sed rats. The vascular responses to HCl were hig hly variable, but second-order arterioles of Tr rats constricted more than those of Sed rats at intermediate-current doses. There were no si gnificant differences between Sed and Tr rats in the vascular response s to adenosine. Both adrenergic vasodilation and vasoconstriction were enhanced in the spinotrapezius muscle of Tr rats, and enhanced adrene rgic vasodilation may contribute to increased functional vasodilation. These observations further demonstrate vascular adaptations in ''nont rained'' skeletal muscle tissues.