Effect of Fibrin Degradation Products and Thrombin on Fibrinogen Synthesis

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Abstract
The effect of i.v. administration of homologous fibrin degradation products [FDP] and thrombin on fibrinogen synthesis was assessed in rabbits. The relative fibrinogen synthesis rate was calculated as a ratio of the amount of radiolabeled lysine incorporated into fibrinogen to the amount incorporated into albumin during the same measurement period. An increase in this ratio above control would indicate a relatively specific stimulation of fibrinogen synthesis as compared with albumin, which was not an acute-phase reactant. Injection of 45 mg of early or late FDP failed to produce a significant increase in the relative fibrinogen synthesis rate, suggesting that FDP play no feedback role in controlling fibrinogen synthesis. Infusion of small amounts of homologous thrombin (15-25 NIH u [National Institute of Health units]) was followed by a small but statistically significant elevation of the relative fibrinogen synthesis rate. This was not accompanied by any increase in the levels of FDP in plasma, or by any decrease in plasma fibrinogen concentration, suggesting that thrombin may possibly stimulate fibrinogen synthesis by a mechanism independent of significant fibrinogenolysis or intravascular coagulation.