Measurement of half-life of human plasma fibrinogen

The plasma fibrinogen half-life (t(1/2)) was measured in a series of adult volunteers by feeding either [¹⁵N]glycine (100-350 mg/hr) or [¹⁵N]ammonium chloride (180-350 mg/hr) plus sodium benzoate (250-500 mg/hr). 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 experiment were run. Initial-rate: the subject took the [¹⁵N]glycine or [¹⁵N]ammonium chloride plus benzoate mixture orally in 8 equal doses over a 3- to 14-hr period. Steady-state: the [¹⁵N]glycine or [¹⁵N]ammonium chloride plus benzoate were taken orally in 10 equal doses over a 10- to 12-hr period. Giving the isotope at a constant rate results in an approximate isotopic steady state in the body's free amino acid pools. For both types of experiment a blood and urine specimen were obtained at the end of the ¹⁵N feeding period. The results of the experiments were: t(1/2) (days), initial-rate with [¹⁵N]glycine, 3.4 ± 1.5 (7), t(1/2) with [¹⁵N]ammonium chloride, 1.4 ± 0.6 (7); t(1/2) steady-state with [¹⁵N]glycine, 2.4 ± 0.6 (5), and with [¹⁵N]ammonium chloride 1.6 ± 0.4 (5). The numbers in parentheses are the numbers of studies. The values obtained with [¹⁵N]glycine were greater than the corresponding [¹⁵N]ammonium chloride values (P < 0.02 for both methods).