Insulin-mediated changes in leg blood flow are coupled to capillary density in skeletal muscle in healthy 70-year-old men

Abstract

The aim of this study was to investigate to what degree the capillarization in the skeletal muscle explains the leg blood flow (LBF) changes during hyperinsulinaemia. Fifteen normotensive men from a population-based cohort of 70-year-old men in Uppsala, Sweden, were investigated. Their metabolic status (oral glucose tolerance test and euglycemic, hyperinsulinaemic clamp test results), serum lipid profile, muscle fiber distribution (myosin adenosine triphosphatase staining), and capillary supply (amylase[ndash ]periodic acid-Schiff method) was evaluated. Doppler ultrasound was used before and after the clamp test to detect insulin-induced changes in LBF. Physiologic hyperinsulinemia (serum insulin, 107 mU/L) caused a moderate increase in LBF (15% [plusmn] 11%; P = .07). Change in LBF was closely related to capillary density ( r = .66; P [lt ] .01) independent of obesity, smoking and level of physical activity. An association was observed between LBF and serum free fatty acid (FFA) concentrations ( r = [minus ].57; P [lt ] .05). In multiple regression analysis, capillary density and serum FFA level together explained 71% of the variation in insulin-mediated LBF changes. Capillary rarefaction and elevated serum FFA values were associated with a vasoconstrictive effect of insulin. In conclusion, capillarization in skeletal muscle and serum FFA concentration seem to be determinants of endothelial function.