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

The research study investigates how exposure to shear force can activate platelets and foster the formation of platelet-platelet and platelet-neutrophil aggregates. This is explored in relation to high and low levels of hematocrit in blood taken from Thoroughbred horses.

Research Methods

• The study was conducted using blood samples drawn from three Thoroughbred horses.
• The volume of packed red blood cells (hematocrit) in each sample was adjusted to either a low level of 32% or a high level of 60%.
• The adjusted blood samples were then subjected to different amounts of shear force, ranging from 11.25 to 750/s, for a duration of 3 minutes using a cone-plate viscometer.
• Flow cytometry, a technique for measuring the physical and chemical properties of cells, was used to identify activated platelets. It was also used to identify the formation of platelet-platelet and platelet-neutrophil aggregates.

Research Findings

• The exposure to shear force resulted in a decrease in the count of platelets, but an increase in the average volume of the platelets.
• Shear force also induced platelet activation and the formation of platelet-platelet and platelet-neutrophil aggregates.
• This effect was more pronounced in blood samples with high hematocrit, where changes were observed at lower shear rates.
• The formation of platelet-neutrophil aggregates was inhibited when P-selectin was blocked. However, the blocking of CD11/CD18 receptors did not show any such effect.

Conclusion

• Shear-induced platelet activation and aggregate formation occur naturally, even under physiologic shear rates.
• The activation of platelets by shear force might explain the aggregates of platelets and neutrophils seen in Thoroughbreds following treadmill exercise. The findings potentially have wider implications for understanding cardiovascular conditions related to shear stress.