Tracer kinetic studies of glucose and alanine metabolism in diabetic dogs on the artificial beta cell.

The in vivo glucose turnover was investigated employing [6-3H]glucose and [U-14C] glucose or [6-3H]glucose and [U-14C]alanine. Fasting chronically diabetic dogs at rest during short-term treatment with a bedside artificial beta cell were compared with normal animals in a glycemic steady state before, during, and after an i.v. load of unlabelled glucose. The insulin was infused into a peripheral vein. During the glucose-controlled insulin infusion glycemia was perfectly normalized, the concentrations of lactate and alanine remained elevated, pancreatic glucagon returned to normal, and the peripheral insulin levels were normal or slightly elevated in the diabetic dogs. Also the glucose turnover was in the normal range but the recirculation of the carbon label (i.e. the Cori cycle activity) was reduced. The alanine turnover and gluconeogenesis from alanine remained increased both in the basal state and during the glucose load. It is concluded that due to the absence of the physiological portosystemic insulin gradient, complete restoration of the physiological metabolic rates and control relations is not possible even if the blood glucose patterns are fully normalized.