Evaluation of platelet activation and platelet-neutrophil aggregates in Thoroughbreds undergoing near-maximal treadmill exercise

OBJECTIVES: To determine whether platelets become activated and form platelet-neutrophil aggregates during near-maximal treadmill exercise in horses. ANIMALS: 4 Thoroughbreds. PROCEDURE: Horses were subjected to 4 standardized exercise tests on a treadmill, and blood samples were collected before exercise, at treadmill speed of 12 m/s, and 5 minutes after exercise. Flow cytometric techniques were used to identify activated platelets, and flow cytometric and microscopic techniques were used to identify platelet-neutrophil aggregates. RESULTS: Platelet-neutrophil aggregates increased from 2.8 +/- 0.4% at rest to 17.2 +/- 1.1% and 14.7 +/- 1.6% during and after exercise, respectively. Platelet activation was not detected during or after exercise. CONCLUSIONS: Platelet-neutrophil aggregates consistently form during strenuous exercise in horses.