Blood coagulation in fish

Blood coagulation systems in cyclostome, elasmobranch, and teleost fish were studied and compared. The plasma of all these fish contained a fibrinogen molecule, capable of being clotted by human thrombin, and a prothrombin molecule, capable of being converted into thrombin which could hydrolyze p-tosyl l-arginine methyl ester. The prothrombin activity could be adsorbed on barium sulfate. Accurate assessment of prothrombin conversion factors is confounded by the "species specificity" of protein-protein interactions, but preliminary observations were made on both the extrinsic and intrinsic clotting schemes. Fish thrombocytes play a central role in the intrinsic conversion of prothrombin to thrombin, and are responsible for clot retraction. The plasma of the smooth dogfish exemplifies a clotting diathesis which can be overcome in vitro by the addition of large amounts of calcium. Under such conditions, other parts of the coagulation scheme become greatly exaggerated, and a very large thrombin generation ensues, subsequently followed by an intense fibrinolysis. A powerful serum inhibition occurs which was shown to be caused by the breakdown products of the fibrinolysis.