Platelet activation defects

Offermanns S, Toombs CF, Hu Y-H, Simon MI (1997) Defective platelet activation in Ga q-deficient mice. Nature 389 183-186... 

VWF in the subendothelium is richer in high molecular weight multimers than the plasma VWF, and is already present in an active conformation for platelets. It has been estimated that subendothelial VWF could guarantee about 40% of total platelet adhesion [32] the plasma VWF, however, would still be necessary to support optimal platelet adhesion [3]. As may readily be deduced, in type 1 von Willebrand disease, the platelet adhesion defect and the severity of the hemoniiagic episodes would be affected by decreased plasma levels, but also by the decrease in subendothelial VWF. 

A femilial platelet function defect has been documented in Simmental cattle (Searcy et al. 1990). Affected cattle have spontaneous epistaxis, and hematomas and hemorrhage following injury. Platelets from affected cattle do not aggregate in response to ADP, collagen, or calcium ionophore. The defect may result from delayed expression of functional fibrinogen binding sites on activated platelets (Frojmovic et al. 1996). 

Yang X, Sun LiGhodiS, Rao AK. Ihanan platelet signaling defect characterized by impaired production of inositol 1,4,5-triphosphate and phosphatidicsicid and diminidtedpleckstrinphosphoiylatkm. Evidence for defective phospholipase C activation. Blocxl 1996 88 1676-1683. 

Commercial or experimental b Trade names in parentheses. c Rapid perfusion (1 h) is feature of all five drugs. d Increased bleeding risks, particularly with invasive procedures, is common to all thrombolytics so are hemostatic defects in clotting and platelet activity. Since obtained from human urine or human kidney tissue cultures. 1 In humans in rabbits only 2-3 minutes. 

Montreal platelet syndrome Apparent defect in calpain, a calcium-activated proteinase protein that may be responsible for spontaneous platelet aggregation... 

Okita, J. R., Erojmovic, M. M., Kristopeit, S., et al., Montreal platelet syndrome A defect in calcium-activated neutral proteinase (Calpain). Blood 74, 715-721 (1989). 

Coagulation defects have been noted with severe hypothermia. These defects include platelet dysfunction, increased fibrinolytic activity, and decreased enzymatic activity necessary for clotting to occur (48,49). However, even mild surface cooling may produce a reversible platelet defect (48,50,51). Mild hypothermia typically reduces metabolism and hepatic clearance of various anesthetic agents and other medications (52). This must be taken into consideration when formulating an anesthetic plan for the hypothermic patient. 

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