Functional adaptations in the skeletal muscle microvasculature to endurance and interval sprint training in the type...

Prevention and treatment of type 2 diabetes includes recommendation to perform aerobic exercise, but evidence indicates that high-intensity exercise training may confer greater benefit. Unique motor recruitment patterns during exercise elicit spatially focused increases in blood flow and subsequent adaptations. Therefore, using 20-wk-old Otsuka Long Evans Tokushima fatty (OLETF) rats with advanced insulin resistance, we examined whether 12 wk of exercise protocols that elicit different motor unit recruitment patterns, endurance exercise (EndEx), and interval sprint training (IST) induce spatially differential effects on endothelial-dependent dilation to acetylcholine (ACh; 1 nM-100 μM) and vasoreactivity to insulin (1-1,000 μIU/ml) in isolated, pressurized skeletal muscle resistance arterioles. Compared with sedentary OLETF rats, EndEx enhanced sensitivity to ACh in second-order arterioles perfusing the "red" (G2A-R) and "white" (G2A-W) portions of the gastrocnemius (EC(50): +36.0 and +31.7%, respectively), whereas IST only increased sensitivity to ACh in the G2A-R (+35.5%). Significant heterogeneity in the vasomotor response to insulin was observed between EndEx and IST as mean endothelin-1 contribution in EndEx was 27.3 ± 7.6 and 25.9 ± 11.0% lower in the G2A-R and G2A-W, respectively. These microvascular effects of exercise were observed in conjunction with training-related improvements in glycemic control (HbA1c: 6.84 ± 0.23, 5.39 ± 0.06, and 5.30 ± 0.14% in sedentary, EndEx, and IST, respectively). In summary, this study provides novel evidence that treatment of advanced insulin resistance in the OLETF rat with exercise paradigms that elicit diverse motor recruitment patterns produce differential adaptive responses in endothelial-dependent dilation and in the complex vascular actions of insulin.