Feline Platelets in Health and Disease and an Assessment of a New Anticoagulant to Minimise Pseudothrombocytopenia and Pseudoleukocytosis

Norman, Elizabeth Jane (2001) Feline Platelets in Health and Disease and an Assessment of a New Anticoagulant to Minimise Pseudothrombocytopenia and Pseudoleukocytosis. MVM(R) thesis, University of Glasgow.

Abstract

Platelets are complex blood cells whose primary function is to participate in haemostasis, aggregating at the site of injury to obstruct blood flow out of the vessel. They are non-nucleated cells, derived by division of multinucleated bone marrow stem cells called megakaryocytes. Production of platelets is increased when the total circulating platelet mass declines, through the action of thrombopoietin and other stimulatory cytokines. Platelets contain a complex cytoskeleton and contractile protein network which enables shape change upon stimulation, active extrusion of the contents of storage granules and clot retraction. Platelets synthesise a number of factors which influence other platelets, the coagulation cascade, leukocytes and blood vessels. These are stored in granules and are extruded upon stimulation along a complex series of channels to reach the exterior. Platelet adhesion and aggregation begins with the binding of proteins to specific glycoprotein receptors in the platelet plasma membrane. Collagen, exposed at the site of damage to blood vessels is an important agonist in vivo, but other agonists are numerous and include substances released from activated platelets themselves, such as adenosine diphosphate (ADP) and serotonin, circulating substances such as adrenalin and vasopressin, products of the coagulation cascade such as thrombin, physical factors such as shear stress and stirring, and many foreign substances. The signal derived from the agonist binding is transferred across the plasma membrane to trigger a series of biochemical events which result in platelet shape change, fibrinogen binding, attachment of platelets in aggregates and secretion of granule contents, which recruit other platelets, and culminates with platelets losing their individual integrity to form a platelet mass. Platelet activity is constrained by the physical nature of the blood vessel wall and substances secreted by platelets and endothelial cells, as well as the rapid inactivation of free agonists. Platelet enumeration is a routine part of a full blood count. Both manual methods, using a haemocytometer, and automated methods are available. Estimations of platelet number can be obtained by counting platelets seen in several microscope fields of the blood smear. Automated methods are more accurate than manual methods because of the larger number of cells counted. However, overlap of feline red cell and platelet size results in inaccuracies when aperture-impedance analysers are used. The presence of platelet aggregates in samples produces inaccuracies by all methods, because individual platelets within aggregates cannot be differentiated. Anticoagulants are designed to inhibit blood coagulation and preserve cell morphology for haematological analysis. EDTA is the most frequently used anticoagulant; however, it causes platelet shape change and swelling and does not completely prevent activation or aggregation. In some individual human blood samples pseudothrombocytopenia and concurrent pseudoleukocytosis is seen when EDTA anticoagulant is used and this has been documented in other species. Other anticoagulants may also produce this effect. Citrate is not routinely used for anticoagulation for haematological analysis because of its dilutional effect. Because of the central role of platelets in haemostasis, changes in platelet number or function can have significant consequences. Immune-mediated thrombocytopenia is a rare disease in the cat in contrast to other species. More commonly, feline thrombocytopenia accompanies other diseases such as neoplasia, gastrointestinal disease and virus infection and may be a component of disseminated intravascular coagulation; however, resultant clinical signs of bleeding are not often seen. A variety of drugs and diseases may affect platelet function including renal disease, liver disease, dysproteinaemias, infectious diseases and disseminated intravascular coagulation. Hereditary platelet function disorders recognised in cats include Chediak-Higashi syndrome and von Willebrand's disease. Platelet neoplasia and thrombocythaemia is rare in cats; however thrombocytosis is not and may reflect physiological release from splenic and non-splenic pools or a reactive component of diseases, resulting in accelerated haematopoiesis, inflammatory diseases, some types of neoplasia or following splenectomy. (Abstract shortened by ProQuest.).

• Item Type: Thesis (MVM(R))
• Qualification Level: Masters
• Additional Information: Adviser: Andrew Nash
• Keywords: Veterinary science
• Date of Award: 2001
• Depositing User: Enlighten Team
• Unique ID: glathesis:2001-76220
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 16:27
• Last Modified: 19 Nov 2019 16:27
• URI: https://theses.gla.ac.uk/id/eprint/76220