Nutrient and hormone delivery to muscle: interactions between insulin and exercise

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Exercise is known to be beneficial in the treatment and prevention of Type 2 diabetes and in particular muscle insulin resistance. Also, exercise and insulin share similar acute actions on muscle. Firstly, muscle contraction has a well established action to increase glucose uptake, and secondly, both muscle contraction and insulin act to increase capillary recruitment. This latter phenomenon is thought to enhance nutrient delivery and waste product removal. There is evidence that the increase in capillary flow due to muscle contraction is accompanied by increases in total blood flow. For insulin action we now have preliminary data to indicate that capillary recruitment occurs within a 5-10 min application of a physiologic dose of insulin independent of a change in total blood flow suggesting a redistribution of flow. Muscle contraction also increases capillary recruitment and it raises the question of whether similar mechanisms underlie insulin- and muscle contraction-induced capillary recruitment or whether there are distinct and complementary pathways. In this project we plan to define the mechanisms responsible for contraction- and insulin-induced capillary recruitment in muscle. We hypothesize that similar mechanisms are operative, with both insulin and muscle contractions acting via NO-dependent mechanisms. Because of capillary reserve, and different initial steps of the signalling systems stimulated by insulin and exercise, capillary recruitment by combined contraction and insulin stimuli will be additive at both sub maximal and perhaps at maximal insulin pathway stimulation. Signalling mechanisms will be compared and the role of non-nutritive route as a flow reserve assessed.