Document Type


Publication Date

Spring 5-15-1964


This investigation was undertaken to develop methods for studying and characterizing the behavior of fibrinogen in healthy animals. For this purpose, two groups, consisting of young (3 to 5 month) and older (6 to 12 month) rabbits, were selected. Homologous rabbit fibrinogen 93 to 97 per cent clottable was prepared by salt fractionation and labeled with I131-iodide. After intravenous injection of the -fibrinogen, the animals were studied for 8 to 10 days. Measurements of the plasma fibrinogen concentration by isotope dilution revealed fluctuations. Plots of the plasma I131-fibrinogen radioactivity against time were fitted by a two or three exponential equation. The excretion of the radioactive breakdown products occurred without delay. A mathematical model based on both these observations and on current knowledge was advanced, and was found to describe the behavior of I.V. I131-ibrinogen. The fractional rate constants were then calculated and used to determine the fluxes of fibrinogen. The transcapillary flux was 171 mg/kg/day in the young and 8l mg/kg/day in the older rabbits. The fibrinogen catabolic flux averaged 56.5 and 39 mg/kg/day in the young and older animals respectively. The interstitial to plasma fibrinogen ratio was 0.20 and 0.36 in the older and young rabbits respectively. The total plasma fibrinogen in 7 older rabbits averaged 106 mg/kg and the total interstitial fibrinogen 22 mg/kg compared with respective values of 118 and k2 mg/kg in the young rabbit. Both, the transcapillary and catabolic fluxes behave as though governed by either an unsaturated or a volumetric clearance system.