Peripheral blood flow and noradrenaline responsiveness: the effect of physiological hyperinsulinemia

Objective: Insulin seems to have vasodilator properties, but it is unclear if insulin in postprandial concentrations is a specific vasodilator of skeletal muscle resistance arterioles only or that various types of vessels are affected. The aim of the present study was to determine the direct effects and the time course of regionalrlocal physiological hyperinsulinemia on skeletal muscle arterioles, skin blood .flow and peripheral venous tone and the reponsiveness of these different vascular beds to noradrenaline. Methods: In protocol 1 ns12 . . .we infused insulin into the brachial artery for 180 min 3.5 mUrmin and evaluated the effects on forearm muscle blood flow FBF . . .and skin blood flow SBF. Furthermore, noradrenaline 0.025, 0.01 and 0.4 mgrmin was infused i.a. at baseline, at 90 and 180 min .after the start of insulin. In protocol 2 ns10 the same regional forearm hyperinsulinemia was achieved, but now the local venous .responsiveness to noradrenaline 1.7–55 ngrmin, at baseline and at 90 and 180 min was measured in a dorsal hand vein. In protocol 3 .we evaluated the local effects of different doses of insulin 1–100 mUrmin infused directly into hand veins preconstricted with . phenylephrine. Results: Forearm hyperinsulinemia f50 mUrl led to a significant increase in FBF after 180 min median 26%, interq..ranges 5–50, P-0.05, while SBF was not altered. Forearm hyperinsulinemia did not affect the noradrenergic responsiveness in skeletal . muscle or skin. Infused locally into hand veins only the highest dose of insulin 100 mUrmin caused a minor venodilation 7% w x.2.4–12.5, P-0.05. Conclusion: Regional forearm physiological hyperinsulinemia has a vasodilator effect on resistance vessels i