Blood platelet economy during moderate and intensive heparin therapy.

By J. F. MUSTARD AND EDMOND A. MURPHY T HE EFFECT OF HEPARIN on the physiology of platelets in vitro has been extensively studied. We share the misgivings of O’Brien1 that results of in vitro studies on coagulation cannot uncritically be applied to effects in vivo. Previous studies in vitro and in extracorporeal circulations2-5 showed that heparin decreases platelet adhesiveness and inhibits the formation of platelet thrombi, and that this effect is sensitive to the level of dosage. Berman6 has reported that the inhibition by heparin therapy of platelet thrombus formation at points of injury in the microcirculation of the hamster is also related to the dosage of heparin used. We have found in experimental studies on thrombus formation that heparin must be given in large doses if it is to be efficacious.7 Recently, however, McDonald and Edgill5 have published some interesting results showing that if 1,500 units of heparin be given twice a week subcutaneously over a period of several months, platelet adhesiveness is greatly reduced. It might be inferred from this that thrombus formation also would be inhibited, because there is good correlation between the platelet adhesive index and the amount of thrombus formed in extracorporeal circulations.” It may be that McDonald and Edgill’s unexpected results are related to the duration of treatment: most other investigators have confined their attention to the acute effects of heparin therapy. \Ve have attempted to obtain more direct evidence of the effect of heparin on platelets undisturbed by removal from the body. The only satisfactory quantitative method we have of studying platelet economy in vivo is the measurement of platelet survival.’” It seemed to be reasonable to study the effect of varying doses of heparin over a prolonged period of time.