Albumin synthetic rate: a comparison of arginine and alpha-ketoisocaproate precursor methods using stable isotope...

The validity of [15N]glycine and [13C]leucine as tracers for investigating albumin fractional synthetic rate (FSR) has been explored by simultaneous infusion of both amino acids into 5 normal female subjects. Albumin FSR, calculated from the urinary [15N]urea plateau value and the incorporation of arginine into albumin was 0.2250 +/- 0.038 per cent/h (mean +/- s.d.). The infusion of leucine, using alpha-ketoisocaproate enrichment to represent the precursor pool, and with measurement of the direct incorporation of leucine into plasma albumin gave a FSR of 0.2516 +/- 0.044 per cent/h. Calculated absolute albumin synthetic rates (ASR) were 11.29 +/- 1.73 mg/kg/h and 11.13 +/- 2.24 mg/kg/h for the glycine and leucine methods respectively. It is concluded that the latter approach is valid as the two amino acids yielded such similar values. The glycine-arginine protocol used represents an improvement compared with previous methods in that the study is completed within 12 h.