Received February 2, 2004
Revised March 10, 2004
Accepted after revision March 18, 2004

¹ University of Piemonte Orientale

^* To whom correspondence should be addressed. E-mail: grossini{at}med.unipmn.it.

	Abstract

Infusion of insulin in anaesthetized pigs has been shown to cause an increase in renal blood flow and a decrease in coronary blood flow which were the net result of a vasoconstriction involving sympathetic -adrenoceptor-mediated mechanisms and of a local vasodilatation involving the endothelial release of nitric oxide. In the present study, the effect of insulin on superior mesenteric blood flow was examined in pentobarbitone-anaesthetized pigs at constant heart rate, aortic blood pressure, left ventricular contractility and blood levels of glucose and potassium. In 10 pigs, infusion of 0.004 IU kg^-1 min^-1 of insulin increased mesenteric flow. In 5 of these pigs, intravenous phentolamine enhanced the increase in mesenteric flow elicited by insulin, a response which was abolished by the subsequent injection of N-nitro-L-arginine methyl ester (L-NAME) into the mesenteric artery. In the remaining 5 pigs, infusion of insulin after intra-mesenteric injection of L-NAME caused a decrease in mesenteric flow. This response was abolished by the subsequent intravenous administration of phentolamine. The present study showed that infusion of insulin in anaesthetized pigs primarily caused a mesenteric vasodilatation which was the net result of two opposite effects involving a predominant vasodilatation mediated by the endothelial release of nitric oxide and a sympathetic vasoconstrictor mechanism mediated by -adrenoceptors.

Key Words: Adrenoceptor, Insulin, Nitric oxide