Mechanisms of the renal vasodilation caused by insulin in anesthetized pigs

The present study was planned to determine the mechanisms involved in the r enal vasodilation caused by insulin. Changes in flow caused by the intraven ous infusion of 0.004 IU/kg/min of insulin at constant heart rate, aortic b lood pressure, left ventricular contractility and blood levels of glucose a nd potassium in the left renal artery were assessed using an electromagneti c flowmeter. In ten pigs, infusion of insulin caused an increase in renal b lood flow which averaged 12.8% of the control values. After hemodynamic var iables had returned to control values, insulin infusion was repeated in fiv e pigs following blockade of a-adrenergic receptors with injection of phent olamine into the renal artery and in the other five pigs following blockade of nitric oxide formation with injection in the same artery of N-omega-nit ro-L-arginine methyl ester (L-NAME). After blockade of alpha -adrenergic re ceptors, insulin infusion caused an increase in renal blood flow which aver aged 12.8% of the control values, being significantly enhanced with respect to the increase previously obtained in the same pigs. On the contrary, aft er blockade of nitric oxide formation insulin infusion caused a decrease in renal blood flow which averaged 6.5% of the control values. These response s were respectively abolished by the subsequent injection into the: renal a rtery of L-NAME and phentolamine. The present study showed that the renal v asodilation caused by insulin in the anesthetized pig was the result of two opposite effects which involved a predominant vasodilation mediated by the release of nitric oxide from the endothelium and a sympathetic vasoconstri ctor mechanism mediated by alpha -adrenergic receptors. (C) 2001 Elsevier S cience Inc. All rights reserved.