EFFECTS OF BACTERIAL ENDOTOXIN ON RABBIT PLATELETS

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Abstract
The platelet factor 3 activity of rabbit platelet-rich plasma (PRP) markedly increases on incubation with Escherichia coli endotoxin as measured by a shortened product I substrate time. Increase of platelet factor 3 activity is maximal by 60-90 minutes of incubation at 37 [degree]C with 100 [mu]g per ml of endotoxin, and occurs to a lesser extent with smaller amounts of endotoxin or at lower temperatures. Components of an antigen-antibody system can replace endotoxin in inducing increased platelet factor 3 activity. No other coagulation activity changes are found upon incubation of PRP with endotoxin. Intravenous injection of 500 to 5,000 [mu]g endotoxin in rabbits induces a shortening of the whole blood silicone clotting time, a profound thrombocytopenia, and increased platelet factor 3 activity demonstrable in platelet poor plasma as well as in PRP. Changes are maximal 1 to 15 minutes after injection and return to normal by one hour. These findings suggest that endotoxin in vitro and in vivo damages intact platelets with a transfer of platelet factor 3 in an active form from platelets to plasma. It seems likely that the action of endotoxin on platelets increasing the availability of platelet factor 3 is at least one mechanism by which endotoxins accelerate coagulation.