Platelet function in the racing thoroughbred: implication for exercise-induced pulmonary hemorrhage

Platelet function was evaluated in horses with exercise-induced pulmonary hemorrhage (bleeder) and in control horses (nonbleeder). Platelet aggregation, secretion, and adhesion to rabbit aortic subendothelium were similar for bleeders and nonbleeders. Platelets readily aggregated in response to ADP, thrombin, collagen, and arachidonic acid, but platelet secretion occurred only with high concentrations of thrombin. Platelets readily adhered to rabbit aortic subendothelium and tended to form large thrombi rather than platelet monolayers or aggregates. These data suggest that horses may be predisposed to thrombus formation and subsequent microvascular obstruction.