Effect of Heparin on Endotoxin-Induced Thrombocytopenia

Abstract

In vitro studies with rabbit platelets have shown that relatively small concentrations of heparin are capable of preventing thrombin induced-platelet injury whereas very large amounts of the anticoagulant are necessary to prevent similar damage by bacterial endotoxin (1). In vivo investigations have demonstrated that the usual anticoagulating amounts of heparin do not prevent the thrombocytopenia in the generalized Shwartzman reaction (gSr) ( 2 ) in rabbits and a similar phenomenon has been observed in humans with septic shock treated with heparin (3, 4). The gSr is elicited by giving rabbits two properly spaced intravenous injections of endotoxin and is characterized by the production of diffuse intravascular coagulation with the subsequent occurrence of bilateral renal cortical necrosis ( 5 ) . I t therefore provides an in vivo model for the study of both endotoxin-and thrombin-induced hematologic changes.The purpose of this investigation was to evaluate the in vivo effect of large amounts of heparin on endotoxin-induced thrombocytopenia, leukopenia and hypofibrinogenemia using the gSr as the experimental model. Material and Methods. E . coli 0127:B8 (Boivin type; Difco Laboratories, Detroit, Michigan) was prepared fresh daily in pyrogen-free normal saline solution.Aqueous heparin, 20,000 units/ml, was purchased from the Upjohn Company, Kalamazoo, Michigan.Rabbits, white hybrid of either sex weighing 1.0 kg were housed in an air-conditioned animal room and fed Purina rabbit pellet and , Ariz. 85721.water, ad lib.The generalized Shwartzman reaction was produced in the classical manner (5). Animals received two intravenous injections of endotoxin (0.1 mg/kg) 24 hr apart. Twentyfour hr after the second endotoxin injection, they were sacrificed and the frequency of bilateral renal cortical necrosis noted.Blood for white blood cell (WBC), platelet, and fibrinogen determination was obtained by two-syringe technique from the heart, and anticoagulated with 3.8% sodium citrate. Plasma was obtained by centrifuging the blood at 8000 rpm at 0" for 20 min. Blood was obtained immediately before (0 hr) and again 4 hr after the second (provocative) injection and the results were compared. WBC counts were done by standard technique, platelet counts by phase microscopy ( 6 ) , and fibrinogen concentation by the method of Ratnoff and Menzie (7).Results. Previous investigations had shown that rabbits are anticoagulated with concentrations of heparin of 5 mg (500 units)/kg or larger when administered intravenously (2). Des Prez reported that in vitro 5.0 mg of heparin/ml of platelet-rich plasma was necessary to inhibit the endotoxin effect on rabbit platelets ( 1). In these in vivo studies, concentrations of heparin ranging from 1000 units to 25,OOO/kg were used. The rabbits weighed 1.0 t 0.1 kg, with hematocrits ranging from 42-45%.All animals received the first injection of endotoxin. Twenty-four hr later they received either (a) endotoxin alone, (b) saline and no endotoxin or heparin, (c) heparin and no endotoxin, or (d) simulta...

Infection-Induced Thrombocytopenia

“…The use of heparin in patients with DIC is controversial. [40][41][42]44,81,158,188 Neither animal nor human studies have convincingly demonstrated a benefit from heparin. Furthermore, heparin is not without risk.…”

Disseminated intravascular coagulation: a review.

“…However, a low platelet count even in an appropriate clinical context does not, in the absence of other supportive findings, necessarily imply DIC. Thrombocytopenia is not uncommon in septicaemia, and in endotoxaemic rabbits low platelet counts occur despite pretreatment with heparin (Corrigan, 1971). …”