Interaction of heparin with canine coagulation proteins: in vivo and in vitro studies.

The effects of heparin on the coagulation profile and on specific factor activity in canine plasma have been examined both in vivo and in vitro. The results show that the prolongation of the partial thromboplastin time of plasma produced by heparin is, at least in part, the result of the interaction of heparin with the intrinsic Factors VIII, IX and XI and the inhibition of their procoagulant activity by heparin. A significant correlation was found between the partial thromboplastin time assay and the circulating heparin activity following intravenous administration of heparin to dogs. The results confirm the suitability of the partial thromboplastin time assay for monitoring heparin therapy in the dog.