Sodium nitroprusside increases human skeletal muscle blood flow, but does not change flow distribution or glucose uptake

1. The role of blood flow as a determinant of skeletal muscle glucose uptak e is at present controversial and results of previous studies are confounde d by possible direct effects of vasoactive agents on glucose uptake. Since increase in muscle blood flow can be due to increased flow velocity or recr uitment of new capillaries, or both, it would be ideal to determine whether the vasoactive agent affects flow distribution or only increases the mean flow. 2. In the present study blood flow, flow distribution and glucose uptake we re measured simultaneously in both legs of 10 healthy men (aged 29 +/- 1 ye ars, body mass index 24 +/- 1 kg m(-2)) using positron emission tomography (PET) combined with [O-15]H2O and [F-18]fluoro-2-deoxy-D-glucose (FDG). The role of blood flow in muscle glucose uptake was studied by increasing bloo d flow in one leg with sodium nitroprusside (SNP) and measuring glucose upt ake simultaneously in both legs during euglycaemic hyperinsulinaemia (insul in infusion 6 pmol kg(-1) min(-1)). 3. SNP infusion increased skeletal muscle blood flow by 86% (P < 0.01), but skeletal muscle flow distribution and insulin-stimulated glucose uptake (6 1.4 +/- 7.5 vs. 67.0 +/- 7.5 mu mol kg(-1) min(-1) control vs. SNP infused leg, not significant), as well as flow distribution between different tissu es of the femoral region, remained unchanged. The effect of SNP infusion on blood flow and distribution were unchanged during infusion of physiologica l levels of insulin (duration, 150 min). 4. Despite a significant increase in mean blood flow induced by an intra-ar terial infusion of SNP, glucose uptake and flow distribution remained uncha nged in resting muscles of healthy subjects. These findings suggest that SN P, an endothelium-independent vasodilator, increases non-nutritive, but not nutritive flow or capillary recruitment.