Platelet Pathology

Platelets play a central role in primary hemostasis. They are also important in pathological processes leading to thrombosis. Antiplatelet drugs are primarily directed against platelets and inhibit platelet activation by a number of different mechanisms. They are used for the prevention and treatment of thrombotic processes, especially in the arterial vascular system. 

L. Gordon and A. J. Milner, Blood platelets as multifunctional cells, in Platelets in Biology and Pathology... 

Platelets play a role in each of the mechanisms of normal hemostasis vasoconstriction, formation of the platelet plug, and blood coagulation. However, they are also involved in pathological processes that lead to atherosclerosis and thrombosis (formation of a blood clot within the vascular system). Antiplatelet drugs interfere with platelet function and are used to prevent the development of atherosclerosis and formation of arterial thrombi. 

Chapter 7 outlines the basic mechanism and treatment of emesis, and in particular, that induced by chemotherapy of cancer. Finally, the chemistry, pharmacology and clinical applications of antagonists of the platelet-activating factor (PAF), an important mediator of many physiological and pathological conditions, are reviewed in Chapter 8. 

It has been hypothesized that depression could arise from a pathological enhancement of 5-HT2 receptor function. This view would concur with the observations that the functional activity of 5-HT2 receptors on the platelet membrane is enhanced in depression and the increase in the density of 5-HT2 receptors in the frontal cortex of brains from suicide victims. It is possible that enhanced 5-HT2 receptor function is associated primarily with anxiety, a common feature of depression, and that the increased activity of the 5-HT2 receptors results in an attenuation of the functioning of S-HT receptors thereby resulting in the symptoms of depression. Whether this change in the activity of S-HT receptors is due to direct effects of the altered 5-HT2 receptor function is uncertain. There is evidence that hypercortisolaemia, which is a characteristic feature of depression, reduces the activity of these receptors probably through central glucocorticoid type 2 receptors. Clearly further research is needed to determine the precise interaction between the 5-HT2 and 5-HTi receptor types. 

The von Willebrandt s factor plays a key role in thrombogenesis. Lack of this factor causes thrombasthenia, a pathologically decreased platelet aggregation. Relative deficiency of the von Wille-Liillmann, Color Atlas of Pharmacology... 

To maintain hemostasis, blood must be retained in the vasculature as fluid. At the same time, blood components must be able to respond rapidly with a clot when a vascular injury occurs. To repair a vascular injury, platelets in blood first adhere as aggregates to the endothelial cells at the affected site and form an initial blood clot. Platelets then stimulate and activate coagulation factors found in plasma to form a more stable fibrin clot. As the injury is resolved and healed, the clot is degraded. Thrombosis is a pathological event wherein a blood clot occludes a blood vessel, resulting in ischemic necrosis of the tissue fed by the blood vessel. Ischemic necrosis involves local anemia and oxygen deprivation. Thrombosis of a coronary artery may lead to myocardial infarction or unstable angina [20]. 

Blanco, C, L. Orensanz-Munoz, C. Blanco-Jerez, and J. Saiz-Ruiz. 1996. "Pathological Gambling and Platelet MAO Activity A Psychobiological Study." American Journal of Psychiatry 153 119-21. 

Carrasco, J. L., J. Saiz-Ruiz, E. Hollander, J. Cesar, and J. J. Lopez-Ibor. 1994. "Low Platelet Monoamine Oxidase Activity in Pathological Gambling." Acta Physiologica Scandinavica 90 427-31. 

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