| Summary: | 博士 === 高雄醫學大學 === 醫學研究所博士班 === 95 === Endotoxemia causes several hematological dysfunctions, including platelet degranulation or disseminated intravascular coagulation, leading to thrombotic and hemorrhagic events which are the main cause of death in patients with sepsis. The aim of this first study was to investigate the mechanisms involved in the platelet aggregation and in their interaction with leukocytes in whole blood after stimulation with endotoxic lipopolysaccharide (LPS) in vitro. Platelet aggregation ability was induced by ADP and measured by an aggregometer. Platelet-rich plasma (PRP) and normal whole blood were incubated with LPS for 30 min, 60 min and 90 min. The results showed that LPS did not directly induce platelet aggregation in PRP. On the contrary, LPS caused a decrease in platelet aggregation that could be detected 90 min after LPS was incubated with the whole blood. Moreoever, both platelet-leukocyte interaction and the platelet hyporesponsiveness can be significantly attenuated by the addition of catalase (H2O2 scavenger) and catalase combined with L-NAME (NG-nitro-L-arginine methyl ester, nitric oxide synthase inhibitor), but not only L-NAME. In the in vitro experimental, these results indicated that LPS-induced phagocytosing leukocytes might influence platelet function suggested a potential role in sepsis and the leukocyte-platelet interaction was attenuated by the H2O2 generation of reactive oxygen radical.
Several studies demonstrated that previous heat shock treatment caused expression of heat-shock proteins (HSPs) and reduced both organ dysfunction and mortality in experimentally induced severe sepsis. However, the protective mechanism of heat shock treatment on platelet function of sepsis remains unclear. The aim of this second study was to investigate the effect of heat shock treatment on platelet aggregation ex vivo in endotoxin-induced septic rats. Rats of the heated group were heated by whole-body hyperthermia 18h before LPS injection. Blood samples were obtained from the carotid artery 90 min after LPS injection. Platelet aggregation ability was measured by an aggregometer. Results revealed that platelet aggregation ex vivo was significantly inhibited in LPS-induced rats in a manner of dose-dependence. Previous heat shock treatment caused overexpression of HSPs and significantly attenuated the LPS-induced platelet hyporesponsiveness. This attenuation disappeared in accordance with absence of leukocyte HSP72 at 7 days after heat shock treatment. Aggregation of normal platelets was also inhibited by incubating with plasma obtained from endotoxemic rats but not from preheated endotoxemic rats. Furthermore, no significant hyporesponsiveness was found in endotoxemic platetlets in addition of preheated endotoxemic plasma. Addition of H2O2 scavenger catalase diminished the platelet hypo-responsiveness significantly only in non-heated endotoxemic rats. Moreover, the plasma nitrite and nitrate level was significantly attenuated in preheated endotoxemic rats. These results revealed that previous heat shock treatment might modulate LPS-induced hypo-responsiveness of platelets by attenuating leukocyte activation and changing the plasma components, possibly through altering the H2O2 and NO concentration.
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