Substrate cardioplegia during hypothermic arrest in the alloxan diabetic dog

In an experimental study, 26 mongrel dogs were treated with alloxan (50 mg per kilogram) to induce fasting hyperglycemia and diabetes. The animals were randomly subdivided into two groups, one of which received 100 mg of propranolol in divided doses for two weeks. The animals underwent sternotomy and were placed on total cardiopulmonary bypass. After aortic cross-clamping, each animal received 10 ml per kilogram of cardioplegic solution. Two different solutions were used, a standard hyperkalemic solution and a high-energy glucose-insulin-potassium (GIK) substrate. Baseline studies were made on the four groups of diabetic animals. Animals given potassium cardioplegia but no propranolol showed statistically significant decreases in cardiac index, heart rate, mean arterial pressure, and minute left ventricular stroke work index after bypass. In contrast, animals given GIK cardioplegia but no propranolol showed no changes in any of these measurements. Animals administered propranolol and potassium cardioplegia experienced decrease in mean arterial pressure from 77.5 +/- 14.1 mm Hg before bypass to 57.5 +/- 17.8 mm Hg after bypass. A similar reduction occurred in animals given propranolol and GIK cardioplegia. However, in this group, the cardiac index increased from 1.78 +/- 0.38 L/min/m2 before bypass to 2.96 +/- 0.73 L/min/m2 after bypass (p less than .006). Similarly, the minute left ventricular stroke work index increased after bypass in these animals. This study demonstrates the protective effect against myocardial ischemia of the addition of substrate to the cardioplegic solution in diabetic animals subjected to aortic cross-clamping during cardiopulmonary bypass, one group receiving propranolol and one group not receiving it.