Increased heparin clearance in experimental pulmonary embolism
Chiu, H.M.; van Aken, W.G.; Hirsh, J.; Regoeczi, E.; Horner, A.A.
Journal of Laboratory and Clinical Medicine 90(1): 204-215
1977
ISSN/ISBN: 0022-2143 PMID: 874367 Document Number: 115149
Patients with pulmonary embolism (PE) were reported to have a shortened heparin half-life (t 1/2). Heparin clearance was investigated in rabbits to explore the possible contribution of platelets to increased heparin clearance in acute PE. Heparin clearance was measured by a heparin activity assay and by 35S radioactivity. Both assay methods gave comparable results. With the heparin activity assay heparin t 1/2 was significantly shorter in PE (12.0 min) than in venous thrombosis (VT) (18.2 min) and in control rabbits (20.2 min) when a heparin dose of 50 units[U]/kg was injected. Heparin t 1/2 was not reduced in animals with PE that were treated with 200 U/kg heparin or in animals that were embolized with polyether urethane coated glass pellets. The role of platelets in the increased heparin clearance in PE was assessed by measuring heparin t 1/2 in thrombocytopenic rabbits, measuring platelet survival times and determining the antiheparin activity of plasma before and after PE. The heparin t 1/2 was shortened to the same extent in thrombocytopenic animals with PE as in nonthrombocytopenic animals (12.8 min compared to 12.0 min) and was significantly shorter than in thrombocytopenic, VT, and control animals (P < 0.005). Platelet survival was uninfluenced by PE, and there was no increase in antiheparin activity in plasma after PE. Heparin t 1/2 is apparently shortened in acute experimental PE. The mechanism for the shortened heparin t 1/2 is apparently not platelet mediated, it is influenced by the nature of the thromboembolic material, and this effect on heparin t 1/2 appears to be dose dependent.