EVIDENCE OF A PROTEIN-C - LIKE ANTICOAGULANT SYSTEM IN BONY FISH

Evidence is presented, confirming the presence of an anticoagulant sys tem in the plasma of Atlantic salmon (Salmo salar L) and rainbow trout (Oncorhynchus mykiss Walbaum) (Order: Teleostei, Family: Salmonidae) that bears striking similarities with the protein C anticoagulant syst em in mammals; its vitamin K-dependence was documented through a warfa rin feeding trial. A potent activator of this system is the protein C activator from the venom of the Central American Moccasin, Agkistrodon bilineatus. When activated, the system splits the tripeptide substrat e glu-pro-arg-pNa, which is the substrate preferred for the in vitro a ssay of human protein C. It also prolongates the plasma activated part ial thromboplastin time, indicating that the system is of clinical rel evance. A temperature dependence of the plasma protein C-like activity was evident, the mean activity being 5- to 10-fold higher, but also m ore variable, in both species in summer and early fall, than it was in winter. There was also a species difference, with rainbow trout havin g the higher levels. In man, subnormal values of protein C implies an increased risk of thrombosis. Whether this applies to fish is not know n. It is, however, a fact that microvascular thromboses are prevalent in farmed Atlantic salmon in winter, whereas thrombotic disease is not a problem in rainbow trout; in the present study plasma protein C-lik e activity was 30% (of a human reference plasma) in salmon at 4 degree s C compared to a level of 60% in rainbow trout. A complicating factor for the assay of protein C-like activity in salmonid. plasma, is the poor stability of the inhibitory system upon storage. Consequently, as says have to be done with freshly prepared citrated plasma.