Shear-induced platelet activation and platelet-neutrophil aggregate formation by equine platelets

Douglas J. Weiss From the Department of Veterinary PathoBiology, University of Minnesota, St Paul, MN 55108.

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Oral A. Evanson From the Department of Veterinary PathoBiology, University of Minnesota, St Paul, MN 55108.

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David McClenahan From the Department of Veterinary PathoBiology, University of Minnesota, St Paul, MN 55108.

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José Fagliari From the Department of Veterinary PathoBiology, University of Minnesota, St Paul, MN 55108.

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Bruce Walcheck From the Department of Veterinary PathoBiology, University of Minnesota, St Paul, MN 55108.

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Abstract

Objectives

To determine whether platelets become activated and form platelet-platelet or platelet-neutrophil aggregates, or both, when subjected to shear.

Sample Population

Blood obtained from 3 Thoroughbreds.

Procedures

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.

Clinical Relevance

Shear-induced platelet activation may explain the exercise-associated platelet-neutrophil aggregates observed in Thoroughbreds undergoing treadmill exercise. (Am J Vet Res 1998;59:1243-1246)

Abstract

Objectives

To determine whether platelets become activated and form platelet-platelet or platelet-neutrophil aggregates, or both, when subjected to shear.

Sample Population

Blood obtained from 3 Thoroughbreds.

Procedures

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.

Clinical Relevance

Shear-induced platelet activation may explain the exercise-associated platelet-neutrophil aggregates observed in Thoroughbreds undergoing treadmill exercise. (Am J Vet Res 1998;59:1243-1246)

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