title: Endotoxin-induced platelet aggregation in heparinised equine whole blood in vitro.
abstract: Endotoxaemia is a leading cause of death among horses. Thrombocytopenia is a common finding in clinical and experimentally-induced cases of endotoxaemia and can lead to coagulopathies, including disseminated intravascular coagulopathy which is usually fatal. In this study it was shown that endotoxin (3 ng ml-1 to 25 micrograms ml-1) can aggregate equine platelets in heparinised whole blood in vitro. The endotoxin-induced aggregation (EIA) was shown to be dependent on the presence of leucocytes in the blood and did not occur when detoxified endotoxin was used, suggesting that lipid A was necessary for the response. Aspirin (1 mmol litre-1) had no effect on EIA whereas apyrase (40 micrograms ml-1) completely abolished it and CV3988 (3 to 30 mumol litre-1) (a competitive antagonist of platelet-activating factor) inhibited the response in a concentration-dependent manner. It is concluded that endotoxin activates equine platelets at low concentrations through an indirect mechanism that involves calcium, leucocytes, adenine nucleotides and platelet-activating factor.
authors.affiliation: University of Cambridge, Department of Clinical Veterinary Medicine.
authors.forename: G E
authors.initials: GE
authors.lastname: Jarvis
authors.forename: R J
authors.initials: RJ
authors.lastname: Evans
mesh_terms: D000818:Animals; D001081:Apyrase / Q000494:pharmacology; D001241:Aspirin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004731:Endotoxins / Q000494:pharmacology*; D006493:Heparin / Q000494:pharmacology; D006736:Horses / Q000097:blood*; D066298:In Vitro Techniques; D008033:Limulus Test / Q000662:veterinary; D008853:Microscopy; D008854:Microscopy, Electron / Q000662:veterinary; D009391:Nephelometry and Turbidimetry / Q000662:veterinary; D010742:Phospholipid Ethers / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors; D010974:Platelet Aggregation / Q000187:drug effects*
chemical_list: D004731:Endotoxins; D010742:Phospholipid Ethers; D010972:Platelet Activating Factor; C037913:CV 3988; D006493:Heparin; D001081:Apyrase; D001241:Aspirin