The effects of insulin on mesenteric blood flow in anaesthetized pigs

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 alpha-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 five 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(omega)-nitro-L-arginine methyl ester (L-NAME) into the mesenteric artery. In the remaining five pigs, infusion of insulin after intramesenteric 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, namely a predominant vasodilatation mediated by the endothelial release of nitric oxide and a sympathetic vasoconstrictor mechanism mediated by alpha-adrenoceptors.