EVIDENCE OF A PROTEIN-C - LIKE ANTICOAGULANT SYSTEM IN BONY FISH (VOL83, PG 389, 1996)

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: TL Teleostei. Family: Salmonida e) that bears striking similarities with the protein C anticoagulant s ystem in mammals; its vitamin K-dependence was documented through a wa rfarin feeding trial. A potent activator of this system is the protein C activator from the venom of the Central American Moccasin, Agkistro don bilineatus. When activated, the system splits the tripeptide subst rate glu-pro-arg-pNa, which is the substrate preferred for the in vitr o assay of human protein C. It also prolongates the plasma activated p artial thromboplastin time, indicating that the system is of clinical relevance. A temperature dependence of the plasma protein C-like activ ity was evident, the mean activity being 5- to 10-fold higher, but als o more variable. in both species in summer and early fall, than it was in winter. There was also a species difference, with rainbow trout ha ving the higher levels. In man, subnormal values of protein C implies an increased risk of thrombosis. Whether this applies to fsh is not kn own. It is, however, a fact that microvascular thromboses are prevalen t in farmed Atlantic salmon in winter, whereas thrombotic disease is n ot a problem in rainbow trout; in the present study plasma protein C-l ike activity was 30% (of a human reference plasma) in salmon at 4 degr ees C compared to a level of 60% in rainbow trout. A complicating fact or for the assay of protein C-like activity in salmonid plasma, is the poor stability of the inhibitory system upon storage. Consequently, a ssays have to be done with freshly prepared citrated plasma.