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 regional/local physiological hyperinsulinemia on skeletal muscle arterioles, skin blood flow and peripheral venous tone and the responsiveness of these different vascular beds to noradrenaline. METHODS: In protocol I (n = 12) we infused insulin into the brachial artery for 180 min (3.5 mU/min) and evaluated the effects on forearm (muscle) blood flow (FBF) and skin blood flow (SBF). Furthermore, noradrenaline (0.025, 0.01 and 0.4 microgram/min) was infused (i.a.) at baseline, at 90 and 180 min after the start of insulin. In protocol 2 (n = 10) the same regional forearm hyperinsulinemia was achieved, but now the local venous responsiveness to noradrenaline (1.7-55 ng/min, 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 mU/min) infused directly into hand veins preconstricted with phenylephrine. RESULTS: Forearm hyperinsulinemia (approximately 50 mU/l) 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 mU/min) caused a minor venodilation (7% 2.4-12.5, P < 0.05). CONCLUSION: Regional forearm physiological hyperinsulinemia has a vasodilator effect on resistance vessels in skeletal muscle, but is slow in onset (180 min). However, skin vasculature and peripheral veins are not affected by this hyperinsulinemia.