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1 Departments of Anatomy & Physiology and Kinesiology, Kansas State University, Manhattan, Kansas, USA
2 Department of Sports Medicine, Pepperdine University, Malibu, California, USA
3 Departments of Medical Pharmacology & Physiology and Veterinary Biomedical Sciences, University of Missouri, Columbia, Missouri, USA
* To whom correspondence should be addressed. E-mail: mcallist{at}vet.ksu.edu.
Endurance exercise training (Ex) has been shown to increase maximal skeletal muscle blood flow. The purpose of this study was to test the hypothesis that increased endothelium-dependent vasodilation is associated with the Ex-induced increase in muscle blood flow. Further, we hypothesized that enhanced endothelium-dependent dilation is confined to vessels in high oxidative muscles that are recruited during Ex. To test these hypotheses, sedentary (Sed) and rats that underwent Ex (30 m/min X 10% grade, 60 min/d, 5 d/wk, 8-12 wk) were studied using three experimental approaches. Training effectiveness was evidenced by increased citrate synthase activity in soleus and vastus lateralis (red section) muscles (P<0.05). Vasodilatory responses to the endothelium-dependent agent acetylcholine (ACh) in situ tended to be augmented by training in the red section of gastrocnemius muscle (RG; Sed: Control, 0.69 ± 0.12 ml/min/100 g/mmHg; ACh, 1.25 ± 0.15; Ex: Control, 0.86 ± 0.17; ACh, 1.76 ± 0.27; 0.05<P<0.10 for Ex vs. Sed during ACh). Responses to ACh in situ did not differ between Sed and Ex for either the soleus muscle or white section of gastrocnemius muscle (WG). Dilatory responses of 2A arterioles from the RG in vitro to flow (4-8 µl/min) and sodium nitroprusside (SNP;10-7 through10-4 M), but not ACh, were augmented in Ex (vs. Sed; P<0.05). Dilatory responses to ACh, flow, and SNP of arterioles from soleus and WG muscles did not differ between Sed and Ex. Content of the endothelial isoform of nitric oxide synthase (eNOS) was increased in 2A, 4A, and 5A arterioles from the RG of Ex; eNOS content was similar between Sed and Ex in vessels from the soleus and WG muscles. These findings indicate that Ex induces endothelial adaptations in fast oxidative/glycolytic skeletal muscle. These adaptations may contribute to enhanced skeletal muscle blood flow in endurance-trained individuals.
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