Age-related changes in conducted vasodilation: effects of exercise training and role in functional hyperemia

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Abstract
Conducted vasodilation may coordinate blood flow in microvascular networks during skeletal muscle contraction. We tested the hypotheses that 1) exercise training enhances conducted vasodilation and 2) age-related changes in the capacity for conduction affect muscle perfusion during contractions. To address hypothesis 1, young (4–5 mo), adult (12–14 mo), and old (19–21 mo) C57BL6 male mice were sedentary or given access to running wheels for 8 wk. Voluntary running distances were significantly different (in km/day): young = 5.8 ± 0.1, adult = 3.9 ± 0.1, old = 2.2 ± 0.1 ( P < 0.05). In gluteus maximus muscles, conducted vasodilation was greater in adult than in young or old mice ( P < 0.05) and greater in young sedentary than in old sedentary mice but was not affected by exercise training. Citrate synthase activity was greater with exercise training at all ages ( P < 0.05). mRNA for endothelial nitric oxide synthase did not differ among ages, but endothelial nitric oxide synthase protein expression was greater in adult and old mice with exercise training ( P < 0.05). Connexin 37, connexin 40, and connexin 43 mRNA were not affected by exercise training and did not differ by age. To address hypothesis 2, perfusion of the gluteus maximus muscle during light to severe workloads was assessed by Doppler microprobe at 3–26 mo of age. Maximum perfusion decreased linearly across the lifespan. Perfusion at the highest workload, absolute and relative to maximum, decreased across the lifespan, with a steeper decline beyond ∼20 mo of age. In this model, 1) exercise training does not alter conducted vasodilation and 2) muscle perfusion is maintained up to near maximum workloads despite age-related changes in conducted vasodilation.