The effect of metabolic control on leucine metabolism in Type 1 (insulin-dependent) diabetic patients

Summary Leucine production rate, metabolic clearance rate and oxidation rate were measured in 10 Type 1 (insulin-dependent) diabetic patients after (1) 24 h insulin withdrawal, (2) conventional insulin therapy and (3) an overnight insulin infusion to maintain normoglycaemia, and in 10 control subjects. In the insulin-withdrawn patients, leucine concentration (259 ± 17 μmol/1), production rate (2.65 ± 0.29 p mol·min⁻¹ kg⁻¹) and oxidation rate (0.69 ± 0.10 μmol · min⁻¹ · kg⁻¹) were significantly greater (p < 0.001;p < 0.05;p < 0.005 respectively) than corresponding values in control subjects (127±6; 1.81 ± 0.12; 0.19 ± 0.02). Following conventional insulin therapy, leucine concentration (162 ± 12 μmol/1) and oxidation rate (0.43 ± 0.05 μmol · min⁻¹ · kg⁻¹) were lower than after insulin withdrawal but were still significantly greater than in control subjects (p<0.05;p<0.005). Although leucine concentration, production rate and metabolic clearance rate were normal after an overnight insulin infusion, leucine oxidation rate was still greater than normal (0.34 ± 0.06 μmol · min⁻¹ kg⁻¹;p<0.05). These results suggest that increased leucine concentration in insulin deficiency is due to elevated leucine production rate caused by increased proteolysis, and that leucine concentration is restored to normal by insulin treatment.