Shear-induced platelet activation and platelet-neutrophil aggregate formation by equine platelets.
OBJECTIVE
To determine whether platelets become activated and form platelet-platelet or platelet-neutrophil aggregates, or both, when subjected to shear.


METHODS
Blood obtained from 3 Thoroughbreds.


METHODS
Blood, with PCV adjusted to 32 (low hematocrit) or 60 (high hematocrit)%, was subjected to shear rates of 11.25, 22.5, 45, 90, 225, and 750/s for 3 minutes by use of a cone-plate viscometer. Flow cytometric techniques were used to identify activated platelets, platelet-platelet aggregates, and platelet-neutrophil aggregates.


RESULTS
Shear resulted in decreased platelet count, increased mean platelet volume, platelet activation, and formation of platelet-platelet and platelet-neutrophil aggregates. These changes occurred at lower shear rates in blood with high hematocrit. Platelet-neutrophil aggregate formation was inhibited by blocking P-selectin, but not CD11/CD18 receptors.


CONCLUSIONS
Shear-induced platelet activation and aggregate formation occur at physiologic shear rates.


CONCLUSIONS
Shear-induced platelet activation may explain the exercise-associated platelet-neutrophil aggregates observed in Thoroughbreds undergoing treadmill exercise.
Department of Veterinary PathoBiology, University of Minnesota, St Paul 55108, USA.
D J
DJ
Weiss
O A
OA
Evanson
D
D
McClenahan
J
J
Fagliari
B
B
Walcheck
D000818:Animals; D001809:Blood Viscosity / Q000502:physiology*; D002449:Cell Aggregation; D048429:Cell Size; D006400:Hematocrit / Q000662:veterinary; D018056:Hemorheology; D006736:Horses / Q000097:blood*; D016177:Macrophage-1 Antigen / Q000378:metabolism; D009504:Neutrophils / Q000166:cytology*; D019007:P-Selectin / Q000378:metabolism; D010805:Physical Conditioning, Animal / Q000502:physiology; D015539:Platelet Activation; D010974:Platelet Aggregation; D010976:Platelet Count / Q000662:veterinary
D016177:Macrophage-1 Antigen; D019007:P-Selectin