Different Hemostatic Responses of Dogs to Heparin Injection. ∗

Abstract

Summary

Observations on bleeding time of 800 dogs after administration of a standard dose of heparin (300 I.I./kg) showed different responses which were divided into 3 groups: 63% as heparin-resistant dogs with normal bleeding time up to 13 minutes; 17% as heparin-intermediate dogs with the bleeding time between 13 and 30 minutes; and 18% as heparin-labile dogs with bleeding times higher than 30 minutes. This response of skin hemostasis does not depend on sex, anesthesia, extensive surgical procedures, heparin brand, or lipemia after olive oil feeding. A heparin-resistant or heparin-labile dog remains such after weeks of observation. The extent of lability varies in individual dogs, some showing an increased bleeding time even with comparatively small doses of heparin. On the other hand, heparin-resistant dogs could be made labile with increased amounts of heparin. It appears that heparin interferes with a plasma component normally active in the hemostatic mechanism. These results emphasize the paramount importance of plasma proteins, rather than a platelet thrombus, as the primary factor in control of skin hemorrhage in the small vessels. The possibility of similar findings in humans is stressed and the possible relationship of heparin-lability and some hemorrhagic accidents in heparinized patients is pointed out.