[Antithrombin III activity in relation to multiple administration of various doses of heparin to normal animals]

Heparin affected the content of antithrombin III and the thrombin time of blood plasma coagulation depending on the dose of the anticoagulant administered (eight intravenous administrations at single doses of 225, 150, 75, 37 or 18 IU/kg of body mass of healthy rats). High doses of heparin decreased more distinctly the content of antithrombin III as compared with low doses. 8 intravenous infusions of small doses of heparin (37 IU/kg) as well as intramuscular administration of the anticoagulant (10 injections) at a dose of 225 IU/kg caused a compensatory increase in content of antithrombin III. After 30 intramuscular administrations the compensatory reaction of antithrombin III disappeared. In this case the content of antithrombin III and the thrombin time of blood plasma coagulation exhibited stability towards the anticoagulant effect.