PERIPHERAL-BLOOD FLOW AND NORADRENALINE RESPONSIVENESS - THE EFFECT OF PHYSIOLOGICAL HYPERINSULINEMIA

Objective: Insulin seems to have vasodilator properties. bur it is unc lear if insulin in postprandial concentrations is a specific vasodilat or of skeletal muscle resistance arterioles only or that various types of vessels art: affected. The aim of the present study was to determi ne the direct effects and the time course of regional/local physiologi cal hyperinsulinemia on skeletal muscle arterioles, skin blood flow an d peripheral venous tone and the reponsiveness of these different vasc ular beds to noradrenaline. Methods: In protocol 1 (n = 12) we infused insulin into the brachial artery for 180 min (3.5 mU/min) and evaluat ed the effects on forearm(muscle) blood flow (FBF) and skin blood flow (SBF). Furthermore, noradrenaline (0.025. 0.01 and 0.4 mu g/min) was infused(i.a.) at baseline, at 90 and 180 min after the start of insuli n. In protocol 2 (n = 10) the same regional forearm hyperinsulinemia w as 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 d orsal hand vein. In protocol 3 we evaluated the local effects of diffe rent doses of insulin (1-100 mU/min) infused directly into hand veins preconstricted with phenylephrine. Results: Forearm hyperinsulinemia ( approximate to 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 al tered. Forearm hyperinsulinemia did not affect the noradrenergic respo nsiveness in skeletal muscle or skin. Infused locally into hand veins only the highest dose of insulin (100 mU/min) caused a minor venodilat ion (7% [2.4-12.5], P < 0.05). Conclusion: Regional forearm physiologi cal hyperinsulinemia has a vasodilator effect on resistance vessels in skeletal muscle, but is slow in onset (180 min). However, skin vascul ature and peripheral veins are not affected by this hyperinsulinemia.