Effects of Bacterial Endotoxin on Rabbit Platelets

Abstract

There is much to suggest that certain of the biologic effects of endotoxins of Gram-negative bacteria are consequences of a reaction involving blood platelets. Thromhocytopenia occurring after injection of endotoxin is well documented (1, 2) and is associated with the appearance of platelet aggregates in pulmonary arterial blood (3). Concomitantly 5-hydroxytryptamine (5HT), which normally circulates virtually completely bound to platelets in an inactive form, appears in plasma in appreciable quantities (4-6). These observations suggest that the interaction of endotoxin and platelets in vivo results in platelet aggregation, trapping of these aggregates in vascular beds, and a transfer of pharmacologically active platelet factors, including 5HT, from platelets to plasma. The studies to be reported herein indicate that platelet aggregation and transfer of 5HT from platelets to plasma can also be observed in vitro during the course of incubation of platelet-rich rabbit plasma with endotoxin. In addition, two other platelet factors, platelet phospholipid and a heat-stabile bactericidin active against Bacillus subtilis, are liberated from platelets during incubation with endotoxin. Materials and MethodsAll glassware was freshly siliconized by immersion in a 1:1000 dilution of Dow Coming Z4141 for 1 hour and was baked for 2 hours at 170°C prior to use. An Escher~hia coli endotoxin of the Boivin type (Difco E. coli endotoxin lot 0127:B8) suspended in saline solution to a concentration of 2 mg per ml was used in all experiments. Several preparations bearing different control numbers of this lot of endotoxin were used and were found to vary somewhat in activity.

Platelets and the Shwartzman Phenomenon

“…In in vitro studies (16)(17)(18), platelets are required for the demonstration of acceleration of eoagtflation. Thrombocytopenia without leucopenia has not been previously studied to evaluate the role of the platelet in the Shwartzman reaction.…”

“…It is possible, therefore, that platelet antiserum may enable localization of platelets in glomerular capillaries and, in that way, provoke the generalized Shwartzman reaction. Evidence has been presented that platelets are importantly concerned with the initiation and/or acceleration of intravascular coagulation resulting in the changes characteristic of the generalized Shwartzman reaction (4,6,16,17). Furthermore, anticoagulation inhibits the generalized Shwartzman reaction (11,12).…”

“…Platelets influence the rate of coagulation (15) and must be present in in ~tro studies to demonstrate acceleration of coagulation by endotoxin or antigenantibody reactions (15)(16)(17)(18). Andcoagulation prevents the Shwartzman reaction, regardless of the anticoagulant used (10)(11)(12).…”

Effects of Bacterial Endotoxin on Rabbit Platelets

“…Piatelet-rich plasma and plateletpoor plasma were prepared by centrifugation as previously described and contained from 4 to 8 X 10 s platelets per milliliter (2). Platelet-rich plasma prepared directly from heparinized blood contained a much lower concentration of platelets due to spontaneous platelet clumping in this anticoagulant under the conditions employed.…”

“…Both in vivo and in vitro studies have further shown that endotoxin causes rapid aggregation and disappearance of blood platelets, accelerates coagulation, and promotes release of several intracellular platelet factors with physiological activity (2)(3)(4)(5). It has thus appeared likely that this platelet-endotoxin ~nteraction may play a role in the earliest phases of removal of endotoxin from the blood stream.…”