Measuring the Coagulability of Fibrinogen in Plasma by Isotopic Means

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Abstract
1. A simple and reproducible technique for measuring the clottability of plasma fibrinogen using iodinated fibrinogen is described, the coefficient of variance being less than 1 %. 2. In vivo experiments in rabbits and monkeys on one hand and in vitro studies with fibrinogens from various species on the other indicated that : a) Aliquots of a fibrinogen preparation iodinated at the same mean substitution level yield practically identical coagulabilities ; b) Aliquots of one labelled preparation when injected into several healthy animals or mixed with their plasmas give equal values for clottability; c) In normal animals, the clottable proportion of the circulating protein-bound radioactivity is at any time a function of the extra/intravascular distribution and of the catabolic rate of fibrinogen relative to the corresponding values of the contaminating labelled protein. 3. The significance of the behaviour of the non-clottable protein-bound radioactivities during fibrinogen turnover experiments for the catabolic mechanism is discussed. It is suggested that fibrinogen catabolism is probably an intracellular process.