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1 Biochemistry, Medical School, University of Tasmania, Hobart, Tasmania, Australia
2 Health Sciences Center, University of Virginia, Charlottesville, Virginia, USA
* To whom correspondence should be addressed. E-mail: Michael.Clark{at}utas.edu.au.
Exercise and insulin increase muscle glucose uptake by different mechanisms and also increase capillary recruitment, which is proposed to facilitate access for hormones and nutrients. The genetically obese Zucker rat shows impaired insulin- but not contraction-mediated glucose uptake in muscle. Recently, we have shown the genetically obese Zucker rats to have impaired insulin-mediated capillary recruitment and proposed that this contributes to the insulin resistance of muscle in vivo. Since this might imply a general loss of recruitable capillaries we now assess responses to contraction in muscles of 18 ± 3 week-old lean and obese Zucker rats in vivo. Field stimulation (2Hz, 0.1ms) was conducted for 1h on one leg of anesthetized instrumented rats and measurements made of femoral blood flow (FBF), heart rate (HR), blood pressure (BP), hind leg metabolism of 1-MX (a measure of capillary recruitment), hind leg glucose uptake (HGU), and lower leg muscle glucose uptake by 2-deoxyglucose (R'g). Lean animals (311 ± 9g) developed tension at 219 ± 27g/g muscle with no change in BP but with significant increases in HR, FBF, HGU, 1-MX metabolism, and R'g (P < 0.05), when compared to non-stimulated control leans. Obese animals (469 ± 7g) developed tension at 265 ± 31g/g muscle with no change in HR or BP, but with significant increases in FBF, HGU, 1-MX metabolism and R'g (P < 0.05), when compared to non-stimulated control obese rats. Muscle contraction of lean animals led to a greater increase in lower leg R'g, similar responses in HGU and 1-MX, and a smaller increase in FBF than obese animals. A tight correlation between FBF and capillary recruitment was noted for all data (P < 0.001). It is concluded that contraction-mediated muscle capillary recruitment and glucose uptake are essentially normal in the obese Zucker rat and the control of FBF and capillary recruitment in exercise are closely linked.
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