Vascular recruitment in skeletal muscle during exercise and hyperinsulinemia assessed by contrast ultrasound

The purpose of this study was to non-invasively quantify the effects of insulin on capillary blood volume (capBV) and RBC velocity (VRBC) in skeletal muscle in vivo with the use of contrast-enhanced ultrasound. We performed contrast ultrasound of the rat hindlimb adductor muscles at baseline and after 2-h infusions of either insulin (3 or 40 mU·kg-1.min-1) or saline. Saline-treated animals were also studied during contractile exercise. VRBC and capBV were calculated from the relation between pulsing interval and video intensity. Femoral artery blood flow, measured by a flow probe, increased with both contractile exercise and insulin. Contractile exercise increased capBV more than twofold and VRBC fivefold. Insulin also increased capBV more than twofold in a dose-dependent fashion but did not significantly alter VRBC. Saline infusion did not significantly alter capBV, VRBC, or femoral artery blood flow. We conclude that physiological changes in skeletal muscle capillary perfusion can be assessed in vivo with the use of contrast-enhanced ultrasound. Exercise increases both VRBC and capBV, whereas hyperinsulinemia selectively increases only capBV, which may enhance skeletal muscle glucose uptake.