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1 Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, USA
* To whom correspondence should be addressed. E-mail: jfrisbee{at}mcw.edu.
Skeletal muscle arterioles from obese Zucker rats (OZR) exhibit oxidant stress-based alterations in reactivity, enhanced 
-adrenergic constriction, and reduced distensibility versus microvessels of lean Zucker rats (LZR). The present study determined the impact of these alterations for perfusion and performance of in situ skeletal muscle during periods of elevated metabolic demand. During bouts of isometric tetanic contractions, fatigue of in situ gastrocnemius muscle of OZR was increased vs. LZR; this was associated with impaired active hyperemia. In OZR, vasoactive responses of skeletal muscle arterioles from the contralateral gracilis muscle were impaired, due in part to elevated oxidant tone; reactivity was improved following treatment with polyethylene glycol-superoxide dismutase (PEG-SOD). Arterioles of OZR also exhibited the increased -adrenergic sensitivity, which was abolished by treatment with phentolamine (10-5 M). Intravenous infusion of phentolamine (10 mg/kg) or PEG-SOD (2000 U/kg) in OZR altered neither fatigue rates nor active hyperemia from untreated levels, however combined infusion improved performance and hyperemia, although not to levels in LZR. Microvessel density in the contralateral gastrocnemius muscle, determined via histological analyses was reduced by ~25% in OZR versus LZR, while individual arterioles from the contralateral gracilis muscle demonstrated reduced distensibility. These data suggest that altered arteriolar reactivity contributes to reduced muscle performance and active hyperemia in OZR. Further, despite pharmacological improvements in arteriolar reactivity, reduced skeletal muscle microvessel density and arteriolar distensibility also contribute substantially to reduced active hyperemia, and potentially to impaired muscle performance.
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