Insulin improves functional and metabolic recovery of reperfused working rat heart

Background. Glucose, insulin, and potassium solution improves left ventricu lar function in refractory pump failure. Direct effects of insulin on the h eart cannot be determined in vivo. We hypothesized that insulin has a direc t positive inotropic effect on the reperfused heart. Methods. Isolated working rat hearts were perfused with buffer containing g lucose (5 mmol/L) plus oleate (1.2 mmol/L). Hearts were subjected to 15 min utes of ischemia and reperfused with or without insulin (100 mu U/mL) for 4 0 minutes. Epinephrine (1 mu mol/L) was added for the last 20 minutes. Results. Hearts recovered 51.1% of preischemic cardiac power in the absence and 76.4% in the presence of insulin (p < 0.05). Whereas oleate oxidation remained unchanged, glucose uptake and oxidation increased during reperfusi on with epinephrine (p < 0.01). This increase was significantly greater whe n hearts were reperfused in the presence of insulin (p < 0.01). Insulin als o prevented an epinephrine-induced glycogen breakdown during reperfusion (p < 0.05). Conclusions. Insulin has a direct positive inotropic effect on postischemic rat heart. This effect is additive to epinephrine and occurs without delay . Increased rates of glucose oxidation and net glycogen synthesis are more protracted. (C) 1999 by The Society of Thoracic Surgeons.