Albumin Synthesis in Premature Infants: Determination of Turnover with [15N]Glycine

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Abstract
Albumin turnover was studied in seven small premature infants who received a constant infusion of [15N] glycine for 60-72 h. Gas chromatography-mass spectrometry was used to measure the rate of appearance of [15N] glycine in albumin isolated from the blood. By comparing the linear increment of [15N]glycine in blood albumin with plateau labelling of urinary [15N]hippurate, which was assumed to reflect intrahepatic isotopic abundance in [15N] glycine, the fractional synthetic rate for albumin was found to be 0.09-0.177 day-1 (mean ± SD = 0.122 ± 0.041 day-1)- The absolute synthesis rate for albumin was 0.3 ± 0.099 g/dl plasma-day-1 and the total plasma synthetic rate was 117.6 ± 37.0 mg/kgday-1. The glycine flux was 326.0-927.7 μmol/kgh1 (mean ± SD 516.7 ± 218.4/umol/kg hr-1'). The percentage of the glycine flux incorporated into albumin in the total vasculature was 0.425 ± 0.344. The fractional synthetic rate and the absolute synthetic rate for albumin in these small premature infants are much higher than values obtained in healthy young adults studied with a similar methodology. The relatively low serum albumin concentrations typical of premature infants appear to be referable to more rapid turnover of a small plasma pool rather than a diminution in the rate of albumin synthesis.