Circulating Alanine Production and Disposal in Healthy Subjects

Circulating-alanine production and disposal rates were estimated in eight healthy postabsorptive subjects by means of U^-14C alanine and U^-14C glucose infusions. The mean circulating-alanine production rate was 368 ± S.E.M. 28 μmol/min. · 1.8². Approximately 50 per cent of circulating-alanine carbon exchanged rapidly with that of circulating lactate. Approximately 30 per cent of circulating alanine exchanged with protein stores. Other disposal was 29 ± 2 per cent to circulating glucose and 40 ± 4 per cent to oxidation. Conclusions: (1) The carbon moieties of circulating alanine and lactate are freely exchangeable. (2) Assessment of the contribution of alanine to gluconeogenesls will depend on establishing the extent to which the precursor pyruvate carbon is derived from glycolysis or from proteolysis. (3) If the principal pyruvate precursor is glycolysis, then the principal specific function of the glucose-alanine cycle appears to be ammonia transport.