Biological activity of endotoxin
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Bacterial endotoxin has a special structure and diverse biological activities, and its performance in the body is more complicated. The common ones are as follows:
1. Cause pyrexia
Experimental studies have found that endotoxicpyrexia is induced by acting on inflammatory cells such as granulocytes and monocytes macrophages to release endogenous pyrogen (EP) such as TNF - α, IL-1 and interferon (INF), inhibit the body's thermoregulatory center and induce fever. The pyrogenicity has the following characteristics:there are species differences; within a certain range, the degree and duration of fever caused by endotoxin will be dose-dependent; tolerance is easy to occur; the pyrogenic activity is not easy to clear.
2. Causes disseminated intravascularcoagulation
Endotoxin can lead to activation of coagulation system, platelet aggregation, increase of fibrin formation and decrease of fibrin degradation in animal body, which can lead to imbalance of coagulation fibrinolysis system, promote thrombosis and diffuse intravascularcoagulation in animal body [19]. Takeuchi et al. [20] successfully reproduced the animal model of endotoxemia using pigs as experimental animals. Wang Tingfuet al. [21] found that in rabbits inoculated with endotoxin of rabbit protoEscherichia coli, there were obvious diarrhea symptoms, vacuolar degeneration of cells and vascular endothelial cells of parenchymal organs such as liver and kidney, and blood stasis, coagulation or DIC could be seen in small bloodvessels and capillaries of the whole body.
3. Cause metabolic disorders
After the endotoxin in the intestinal cavityenters the blood system, it can cause the animal to develop hyperglycemiafirst, and then turn to hypoglycemia, causing a large amount of glycogenconsumption. This process may be related to the excessive secretion of adrenaline. In addition, due to microcirculation obstacles, tissue ischemia and hypoxia, which cause a large amount of lactic acid to accumulate and cause metabolic acidosis in the body. It can also cause the redistribution and distribution of copper, iron, zinc and other trace elements in various tissues and organs.
4. Cause endotoxemia
Endotoxemia is caused by a large amount of endotoxin released or dead and lysed by bacteria in the blood or in a lesion entering the blood system, or intravenous infusion of a large amount of endotoxin-contaminated liquid during infusion, which causes physiological changes in the body.
The clinical symptoms mainly include fever, changes in the number of white blood cells, heart failure, and decreased liver and kidney function, severe neurological symptoms, and shock. After the endotoxin enters the blood circulation, it activates the release of active substances in the blood vessels, causing the body's capillaries to dilate, reducing cardiac output, and greatly reducing venous return blood, which in turn causes the animal's blood pressure to drop, and tissue perfusion is insufficient.Tissue ischemia and hypoxia.
In addition, endotoxin circulating in the blood can activate immunologically active cells such as lymphocytes, macrophages, neutrophils, and monocytes, as well as the cytokines TNF, INF-1, IL-1, and IL produced by the corresponding target cells. -6, IL-21, etc., can be used as an immune complex adjuvant; severely can lead to premature delivery, miscarriageor stillbirth in pregnant animals; it can also affect the production of redblood cells and the reduction of early neutrophils, and later secondary to granulocytes Hyperemia; in addition, it can activate complement and cause various reactions related to complement-mediated.