Understanding and Evaluating Platelet Function

Abstract

The contribution of platelets to normal hemostasis and vascular disease is well described. However, recent studies make it clear that much remains to be learned about platelet activation at the single cell and the molecular level, and about the contribution of platelets to inflammation, tumor angiogenesis, and embryonic development. This article is divided into two themes. The first is an overview of current knowledge of the mechanisms that drive platelet function in vivo and a brief summary of some of the emerging ideas that are modifying older views. The second theme is a consideration of the strengths and weaknesses of the tools we have as hematologists to assess platelet function in the clinical setting, identify mechanisms, and evaluate the impact of antiplatelet agents.Although fish, birds, and presumably dinosaurs make do with nucleated thrombocytes as the cellular component of hemostasis, platelets evolved in mammals as a specialized means to seal leaks in a high-pressure, high-flow circulatory system. Many of the most pertinent properties of platelets-including their shape, the contents of their secretory granules, their high density of regulatable adhesion receptors, and their ability to promote thrombin generation-are dictated by the requirements of forming a stable hemostatic plug under high-flow conditions. Circulating platelets must be able to sustain repeated contact with the normal vessel wall without premature activation, recognize the unique features of a damaged wall, cease forward motion upon recognition of damage, adhere despite the forces produced by continued blood flow, and cohere to each other, forming a stable plug of the correct size that can remain in place until it is no longer needed. This brief review considers some of the current ideas about platelet activation and the evaluation of platelet function in the research and clinical settings.

Regenerative Endodontics: An Evidence Based Review

“…The access cavity is sealed afterwards and the patient is recalled every three months for radiographic and clinical examination. The most obvious advantage of using PRP is the fact that the concentration of platelets in PRP is about 1million per microliter which is much more than normal blood clot [60] . It also has a much higher concentration of growth factors than normal blood clot [61] .…”

The Thrombogenic Role of Platelets in Valvular Atrial Fibrillation

“…In the arterial circulation, higher flow rates limit fibrin formation by washing out soluble clotting factors. Platelets, which work best at higher shear rates, help to form a physical barrier against further blood loss and, at the same time, provide a surface on which thrombin is generated and fibrin can accumulate (Brass, 2010). The formation of a stable platelet plug following vascular injury is often described as occurring in three distinct stages: (1) initiation, (2) extension, and (3) stabilization (Figure 1).…”

“…Examples include outside-in signaling through integrins and signaling through receptors whose ligands are located on the surface of adjacent platelets. The net result is a hemostatic plug comprised of activated platelets embedded within a cross-linked fibrin mesh, a structure stable enough to withstand the shear forces generated by flowing blood in arterial circulation (Brass, 2010). close contacts between platelets in the growing hemostatic plug, along with a fibrin meshwork (shown in red), help to perpetuate and stabilize the platelet plug.…”

Development of alternative HPLC method for determination of tirofiban in rat serum

“…Thus, the benefits of tirofiban in those with acute coronary syndromes may be due to rapid endothelization of damaged vessel, besides antiplatelet effects [1]. Platelet aggregation inhibition [8] is reversible following cessation of the infusion of Tirofiban. Tirofiban has a rapid onset and short duration of action when administered intravenously, with a half-life of approximately 2 hours.…”