Experimental diabetes in the baboon.

Abstract

The object of the present study was to determine simultaneously aspects of hepatic and peripheral glucose metabolism in the intact baboon. Isotopic techniques were used to study glucose turnover rates, glucose recycling, glucose pool and space, and the forearm technique to study peripheral exchange of glucose. The results obtained in the normal animals acted as reference values for each animal. Thereafter diabetes mellitus was produced with streptozotocin, a drug causing destruction of the beta cells of the pancreatic islets. Experiments were then repeated in the acutely diabetic baboon and the nature and extent of the abnormalities in glucose metabolism documented. Lactate metabolism and peripheral lipid metabolism were included in the study in order to establish any interrelationships with glucose metabolism and to determine the abnormalities resulting from the production of diabetes. In the normal animal the turnover rate of lactate was greater than glucose although the lactate pool was much smaller than the glucose pool. After producing diabetes glucose turnover rates increased threefold and correlated with the severity of hyperglycaemia. A significant increase in lactate turnover rates was noted but the increase was less than in the case of glucose turnover rates. The formation of glucose from lactate increased significantly but the fraction of the lactate turnover rate converted to glucose was unchanged. The glucose pool increased nearly threefold and correlated with the increase in glucose turnover rate. There was a significant but smaller increase in lactate pool which correlated with the increase in lactate turnover rate. Both glucose and lactate space decreased after diabetes but the decrease did not correlate with the severity of hyperglycaemia. In the majority of diabetic animals there was no glucose utilization in the forearm, and in fact glucose release was observed. Increased production of lactate occurred in the forearm of the diabetic baboon, despite decreased glucose utilization.Arterial levels of triglyceride and free fatty acid increased threefold after diabetes while the free glycerol level doubled. In the normal animal the general pattern of exchange in the forearm consisted of triglyceride and free fatty acid uptake and free glycerol release. In the diabetic animal triglyceride and free fatty acid release was observed, while the release of free glycerol was decreased. The pattern of forearm metabolism in the diabetic animals was variable and not as consistent as before the production of diabetes. Several interrelationships between glucose, lactate and lipid metabolism were noted. The baboons used in this study showed extreme sensitivity to the metabolic effects of Streptozotocin Diabetes. Hyperglycaemia increased in severity and ketoacidosis invariably developed in the second week. The animals were not treated with insulin and death from severe uncontrolled diabetes occurred in nearly all animals within two weeks. This study has demonstrated the severe abnormalities in hepatic and peripheral glucose metabolism in diabetes. The simultaneous pathogenesis of these abnormalities and their importance in the development of the acute diabetic syndrome have been defined. Associated abnormalities in lactate metabolism and lipid metabolism have also been documented.