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Increased incidence of thrombosis after anticoagulants has been reported intermittently. The present work utilizes a new technique for studying the effect of various drugs and procedures on thrombus production in rats. Two hundred and forty rats in lots of 24 were given single or repeated intravenous injections of saline or heparin. At various intervals after clotting times had returned to normal, the jugular vein was bared, 10% formalin solution applied, and the incision closed. Four hours later veins were examined for clots. Rats receiving heparin averaged 73.9% thrombosis. Those receiving saline averaged 58.6% thrombosis. The differences between the groups were consistent. A single high dose of heparin given 1 minute before the operation reduced the incidence of thrombosis to 16%. Tests for platelet stickiness on blood taken from rats 4 and 24 hours after heparin injection showed that heparin had not caused increased stickiness in rat platelets over these periods.
J. G. Ashwin (1962) studied this question.