Leucine-induced hypoglycemia: II. Studies concerning other amino acids and leucine metabolites*

Summary Two infants with leucine-sensitive hypoglycemia have been studied to elucidate the specificity and mechanism of action of l -leucine. Sixteen other naturally occurring l -amino acids have been administered intravenously and tyrosine and tryptophan by gavage. Of these amino acids, only l -leucine consistently induced hypoglycemia. d -leucine also produced hypoglycemia when given intravenously. Alpha-ketoisocaproic and isovaleric acids were administered intravenously; the former induced hypoglycemia whereas the latter did not. Monocarboxylic keto-acids in the urine were measured following l -leucine or alphaketoisocaproic acid loading. The recovery of keto-acids in the urine was of a low order, similar to that of a control subject indicating no metabolic defect in the conversion of alpha-ketoisocaproic acid to isovaleric acid. Preliminary evidence is presented that leucine administration to affected patients results in increased circulating insulin levels.