This report describes sensitive, precise microtechniques that allow quantification of glucose and alanine metabolism in vivo using stable isotope tracers. By combined gas chromatography-mass spectrometry and selected ion monitoring—deuterium and carbon-13 enrichment in blood glucose and alanine were measured with an error of less than 2 per cent. Estimation of glucose and alanine flux in dogs by stable isotope tracer techniques was compared with simultaneous measurements made in the same animal with conventional radiotracer dilution methods. Application of the described stable isotope methods to determination of glucose and alanine turnover as well as alanine-2,3-l3C incorporation into glucose In adult men confirmed the safety and validity of these techniques for human investigation.

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