Effects of aging and exercise training on spinotrapezius muscle microvascular PO2 dynamics and vasomotor control

McCullough DJ, Davis RT III, Dominguez JM II, Stabley JN, Bruells CS, Behnke BJ. Effects of aging and exercise training on spinotrapezius muscle microvascular PO2 dynamics and vasomotor control. J Appl Physiol 110: 695-704, 2011. First published January 6, 2011; doi:10.1152/japplphysiol.01084.2010.-With advancing age, there is a reduction in exercise tolerance, resulting, in part, from a perturbed ability to match O-2 delivery to uptake within skeletal muscle. In the spinotrapezius muscle (which is not recruited during incline treadmill running) of aged rats, we tested the hypotheses that exercise training will 1) improve the matching of O-2 delivery to O-2 uptake, evidenced through improved microvascular PO2 (PmO2), at rest and throughout the contractions transient; and 2) enhance endothelium-dependent vasodilation in first-order arterioles. Young (Y, similar to 6 mo) and aged (O, > 24 mo) Fischer 344 rats were assigned to control sedentary (YSED; n = 16, and OSED; n = 15) or exercise-trained (YET; n = 14, and OET; n = 13) groups. Spinotrapezius blood flow (via radiolabeled microspheres) was measured at rest and during exercise. Phosphorescence quenching was used to quantify PmO2 in vivo at rest and across the rest-to-twitch contraction (1 Hz, 5 min) transition in the spinotrapezius muscle. In a follow-up study, vasomotor responses to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) stimuli were investigated in vitro. Blood flow to the spinotrapezius did not increase above resting values during exercise in either young or aged groups. Exercise training increased the precontraction baseline PmO2 (OET 37.5 +/- 3.9 vs. OSED 24.7 +/- 3.6 Torr, P < 0.05); the end-contracting PmO2 and the time-delay before PmO2 fell in the aged group but did not affect these values in the young. Exercise training improved maximal vasodilation in aged rats to acetylcholine (OET 62 +/- 16 vs. OSED 27 +/- 16%) and to sodium nitroprusside in both young and aged rats. Endurance training of aged rats enhances the PmO2 in a nonrecruited skeletal muscle and is associated with improved vascular smooth muscle function. These data support the notion that improvements in vascular function with exercise training are not isolated to the recruited muscle.