Abstract 1138: The Effect of Insulin on Cardiac Function and Glucose Oxidation in Newborn Rabbit Hearts Perfused with High and Low Fatty Acid Concentrations
In adult hearts, insulin enhances cardiac functional recovery following surgical ischemia by augmenting glucose oxidation (GOX) while inhibiting fatty acid oxidation. However, high free fatty acid levels inhibit insulin’s post-ischemic cardioprotection. Although insulin is used clinically in newborn cardiac surgery, its effects on cardiac metabolism and functional recovery are unknown and may differ from adults due to low GOX and greater reliance of the heart on fatty acid oxidation in the post-natal period. We examined insulin’s effect on cardiac metabolism and function in isolated working hearts from 7-day-old rabbits, perfused ± 0.1 U/L or 10 U/L insulin (added 2 min prior to global ischemia) in high fat (F-H: 1.2 mmol/L palmitate) or low fat (F-L: 0.4 mmol/L palmitate) with 11 mmol/L glucose, 2.5 mmol/L Ca2+, and 3% BSA. The hearts were subjected to a 30-min aerobic perfusion followed by a 30-min global no flow normothermic ischemia and 40 min of aerobic reperfusion. F-L hearts perfused with 0.1 U/L, 10 U/L, or no insulin show similar GOX rates. F-H hearts with 0.1 U/L or no insulin showed only small non-significant increases in GOX rates. Unlike adult hearts, in the presence of insulin, GOX rates in F-H and F-L hearts were similar pre- or post-ischemia. F-L perfusions with or without insulin show similar recovery. Without insulin, F-H perfusions show significantly better cardiac function than F-L. We conclude that unlike adult hearts, where insulin increases cardiac function and GOX, these effects are not paralleled in the newborn heart perfused with F-L or F-H. Of interest is that in F-H hearts, insulin was not cardioprotective, but rather showed a decrease in recovery. This may be due to the increased reliance of the newborn heart on fatty acid oxidation and has implications on the clinical use of insulin during newborn heart surgery.