Splanchnic and systemic hemodynamic effects of sustained euglycemic hyperinsulinemia in rats

Insulin, in addition to its metabolic function, was found to induce skeletal muscle vasodilatation after acute administration. The vasoactive effects of sustained euglycemic hyperinsulinemia, especially in the splanchnic circulation, are less well known. The aim of this study was to evaluate the systemic and splanchnic hemodynamic effects of sustained euglycemic hyperinsulinemia. Hyperinsulinemia was induced by a sustained-release insulin implant in the scurf area of male rats (release rate -1 U/day). Beginning on the 3rd day, the study group was fed a glucose-rich diet. Hemodynamic studies were performed on the 5th day using the radioactive microsphere technique. Serum insulin was measured by radioimmunoassay. At the time of the hemodynamic measurements, plasma insulin level was higher in the insulin-treated (n=8) compared to control rats (n=8) (23.6 +/- 4.7 vs. 13.2+/-3.9 microu/mL, respectively; p<0.001). Plasma glucose level of the two groups was similar (5.43 +/- 1.07 vs. 5.83 +/- 1.44 mmol/L, respectively). Abdominal skeletal muscle blood flow was higher in the insulin-treated group (0.11 +/- 0.05 vs. 0.05 +/- 0.04 mL x min(-1) x g(-1), respectively; p<0.02). No significant changes were observed in cardiac output and renal blood flow. In the splanchnic circulation: stomach, pancreatic, intestinal, splenic, hepatic arterial and total hepatic blood flow were also not significantly different. In summary, short-term, sustained euglycemic hyperinsulinemia in rats increased blood flow to skeletal muscle but had no hemodynamic effects on cardiac output or splanchnic circulation.