Measurement of half-life of human plasma fibrinogen

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Abstract
The plasma fibrinogen half-life (t1/2) was measured in a series of adult volunteers by feeding [15N]glycine (100-350 mg/h) or [15N]ammonium chloride (180-350 mg/h) plus sodium benzoate (250-500 mg/h). The 15N enrichment of the hepatic fibrinogen amino acid precursor pool was estimated from the 15N enrichment of the urinary hippuric acid. The amount of isotope incorporated into fibrinogen was found by measuring the 15N enrichment of glycine incorporated into fibrinogen. Two types of experiments were run. In the initial-rate, the subject took the [15N]glycine or [15N]ammonium chloride plus benzoate mixture orally in 8 equal doses over a 3-4 h period. In the steady-state, the [15N]glycine or [15N]ammonium chloride plus benzoate were taken orally in 10 equal doses over a 10-12 h period. Giving the isotope at a constant rate results in an approximate isotopic steady state in the body''s free amino acid pools. A blood and urine specimen were obtained at the end of the 15N feeding period. The results of the experiments were as follows: t1/2 (days), initial-rate with [15N]glycine, 3.4 .+-. 1.5, t1/2 with [15N]ammonium chloride, 1.4 .+-. 0.6; t1/-2 steady-state with [15N]glycine, 2.4 .+-. 0.6 and with [15N]ammonium chloride 1.6 .+-. 0.4. The values obtained with [15N]glycine were greater than the corresponding [15N]ammonium chloride values (P < 0.02 for both methods).