Effect of intravenous insulin treatment on in vivo whole body leucine kinetics and oxygen consumption in insulin-deprived type I diabetic patients.

In vivo leucine metabolism was studied after an overnight fast in nine type I diabetic patients and nine healthy control subjects using L-[1-13C] leucine as a tracer. In the insulin-deprived state, leucine flux (reflecting proteolysis), leucine oxidation, and plasma leucine concentrations were higher in the diabetic patients than in the control subjects (P less than .001). In 4 of the 9 insulin-deprived diabetic patients, a four-hour intravenous insulin treatment decreased plasma glucose and leucine concentrations and leucine flux, but failed to decrease leucine oxidation. In the remaining 5 of the 9 diabetic patients, uninterrupted insulin treatment prior to the study and a seven-hour intravenous insulin treatment during the study period decreased not only the concentrations of plasma glucose and leucine and leucine flux, but also leucine oxidation (P less than .01). In all 9 diabetic patients the nonoxidative portion of leucine flux (reflecting protein synthesis) decreased during insulin treatment (P less than .01), but this decrease was lower than that of leucine flux (reflecting proteolysis), and therefore protein was conserved during insulin treatment. We conclude that the effect of insulin on proteolysis (reflected by leucine flux) is more rapid than its effect on leucine oxidation, but on aggressive insulin treatment accelerated leucine oxidation also was decreased in type I diabetic patients.