Direct measurements of the permeability surface area for insulin and glucose in human skeletal muscle

To elucidate mechanisms regulating capillary transport of insulin and glucose, we directly calculated the permeability surface (PS) area product for glucose and insulin in muscle. Intramuscular microdialysis in combination with the forearm model and blood flow measurements was performed in healthy males, studied during an oral glucose tolerance test or during a one-step or two-step euglycemic hyperinsulinemic clamp. PS for glucose increased significantly from 0.29 +/- 0.1 to 0.64 +/- 0.2 ml/min.100 g after oral glucose tolerance test, and glucose uptake increased from 1.2 +/- 0.4 to 2.6 +/- 0.6 micro mol/min.100 g (P < 0.05). During one-step hyperinsulinemic clamp (plasma insulin, 1.962 pmol/liter), PS for glucose increased from 0.2 +/- 0.1 to 2.3 +/- 0.9 ml/min.100 g (P < 0.05), and glucose uptake increased from 0.6 +/- 0.2 to 5.0 +/- 1.4 micro mol/min.100 g (P < 0.05). During the two-step clamp (plasma insulin, 1380 +/- 408 and 3846 +/- 348 pmol/liter), the arterial-interstitial difference and PS for insulin were constant. The PS for glucose tended to increase (P = not significant), whereas skeletal muscle blood flow increased from 4.4 +/- 0.7 to 6.2 +/- 0.8 ml/min.100 ml (P < 0.05). The present data show that PS for glucose is markedly increased by oral glucose, whereas a further vasodilation exerted by high insulin concentrations may not be physiologically relevant for capillary delivery of either glucose or insulin in resting muscle.