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Exercise training reverses age-related decrements in endothelium-dependent dilation in skeletal muscle feed arteries

¹Department of ¹Health and Kinesiology and of ²Veterinary Physiology and Pharmacology, Texas A&M University, College Station, Texas; and ³Department of Biomedical Sciences, University of Missouri, Columbia, Missouri

Submitted 15 September 2008 ; accepted in final form 16 March 2009

We tested two hypotheses, first that exercise training reverses age-related decrements in endothelium-dependent dilation in soleus muscle feed arteries and second that this improved endothelium-dependent dilation is the result of increased nitric oxide (NO) bioavailability due to increased content and phosphorylation of endothelial NO synthase (eNOS) and/or increased antioxidant enzyme content. Young (2 mo) and old (22 mo) male Fischer 344 rats were exercise trained (Ex) or remained sedentary (Sed) for 10–12 wk, yielding four groups of rats: 1) young Sed (4–5 mo), 2) young Ex (4–5 mo), 3) old Sed (24–25 mo), and 4) old Ex (24–25 mo). Soleus muscle feed arteries (SFA) were isolated and cannulated with two glass micropipettes for examination of endothelium-dependent (ACh) and endothelium-independent [sodium nitroprusside (SNP)] vasodilator function. To determine the mechanism(s) by which exercise affected dilator responses, ACh-induced dilation was assessed in the presence of N-nitro-L-arginine (L-NNA; to inhibit NO synthase), indomethacin (Indo; to inhibit cyclooxygenase), and L-NNA + Indo. Results indicated that ACh-induced dilation was blunted in old Sed SFA relative to young Sed SFA. Exercise training improved ACh-induced dilation in old SFA such that vasodilator responses in old Ex SFA were similar to young Sed and young Ex SFA. Addition of L-NNA, or L-NNA + Indo, abolished the exercise effect. Immunoblot analysis revealed that extracellular superoxide dismutase (SOD) protein content was increased by training in old SFA, whereas eNOS and SOD-1 protein content were not altered. Addition of exogenous SOD, or SOD + catalase, improved ACh-induced dilation in old Sed SFA such that vasodilator responses were similar to young Sed SFA. Addition of L-NNA abolished the effect of exogenous SOD in old Sed arteries. Collectively, these results indicate that exercise training reverses age-induced endothelial dysfunction in SFA by increasing NO bioavailability and that increases in vascular antioxidant capacity may play an integral role in the improvement in endothelial function.

endothelial dysfunction; endothelial nitric oxide synthase; superoxide dismutase

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