Aims/hypothesis: Insulin possesses vasodilatory actions that may be important in regulating its access to insulin-sensitive tissues. Our study aims to directly measure changes in response to insulin in the human skeletal muscle microcirculation. Measurement was by an implanted laser Doppler probe.
Methods: We investigated changes in intramuscular and skin microvascular perfusion in 12 healthy individuals during a hyperinsulinaemic and a control clamp. We determined leg blood flow with plethysmography, finger skin functional capillary recruitment with capillaroscopy, endothelium-(in)dependent vasodilation by iontophoresis of acetylcholine and sodium nitroprusside, and leg intramuscular reactive hyperaemia and vasomotion with laser Doppler measurements.
Results: Compared to the control study, hyperinsulinaemia (416+/-82 pmol/l) caused: (i) an increase in leg blood flow (1.0+/-1.0 vs 0.1+/-0.6 ml.min(-1).100 ml, p<0.05); (ii) an increase in finger skin capillary recruitment (14.9+/-10.1 vs -5.6+/-11.0%, p<0.01); (iii) no change in baseline laser Doppler perfusion either in finger skin or leg muscle; (iv) a tendency to increase acetylcholine-mediated vasodilation (475+/-534 vs 114+/-337%, p=0.07) with no change in sodium-nitroprusside-mediated vasodilation ( p=0.2) in finger skin; (v) an increase in intramuscular reactive hyperaemia (423+/-507 vs 0+/-220%, p<0.01); and (vi) a decrease in time needed to reach peak intramuscular perfusion (-3.6+/-3.0 vs 1.1+/-3.1 s, p<0.01). In addition, hyperinsulinaemia induced an increase in intramuscular vasomotion by increasing the contribution of frequencies between 0.01 and 0.04 Hz ( p<0.05 for all), which probably represents increased endothelial and neurogenic activity.
Conclusions/interpretation: Physiological hyperinsulinaemia not only stimulates total blood flow and skin microvascular perfusion, but also augments human skeletal muscle microvascular recruitment and vasomotion as detected directly by laser Doppler measurements.