Study On The Development Of Hepatic Fibrosis Promoted By Chronic Psychological Stress In Rats Via Intestinal Route

BackgroundHepatic fibrosis is practically a necessary process for many chronic liver diseases developing into cirrhosis.It has been proved that chronic psychological stress can lead to the aggravation of hepatitis and promote the development of hepatic fibrosis,but the specific mechanism is not clear.Traditionally,chronic psychological stress is supposed to affect the liver directly.The hypothalamus-pituitary-adrenal axis has been activated and the glucocorticoid is released under chronic psychological stress.These responses would lead to the imbalance of immune system,the aggravation of inflammation in body and liver,high expression of Fas antigen in hepatocytes,acceleration of hepatocyte apoptosis and decrease of liver blood flow,in which way the occurrence and development of liver fibrosis are promoted.However,some studies have found that the effects of psychological stress on the liver are different in vivo and in vitro.In vivo environment,the release of glucocorticoid and the expression of Fas antigen in hepatocytes increased,and the apoptosis of hepatocyte accelerated under psychological stress.However,the expression of Fas antigen in hepatocytes did not increase and the apoptosis was not obvious when the hepatocytes were cultured in vitro glucocorticoid environment.It is not clear exactly in which way the chronic psychological stress acts on liver.As we know,there is an extremely complicated communication mechanism between brain and intestine,called brain-intestine axis,which is a comprehensive physiological model integrating gastrointestinal system and brain.Excessive or harmful psychological stress can disorder the brain-intestine axis,resulting in intestinal dyskinesia,increase of intestinal sensitivity and permeability and the dysfunction of intestinal barrier.These pathological changes can act on the intestinal-liver axis and will lead to the translocation of intestinal bacterial products such as LPS to the extraintestinal,resulting in inflammatory cascade reaction in the liver,which make important contributions to the liver cirrhosis and its complications.We have noticed that the intersection of brain-intestine axis and intestine-liver axis lies in the intestine.Therefore,we assume that chronic psychological stress may act on the liver through intestinal tract.We propose the concept of brain-intestine-liver axis to explain the liver fibrosis promoting effect of chronic psychological stress.ObjectiveTo observe the effect of chronic psychological stress on intestinal permeability and bacterial translocation in rats,and study the effect of chronic psychological stress on the development of liver fibrosis in rats via intestinal route.MethodsSixty SD rats were randomly divided into 6 groups: normal group,psychological stress group,olive oil group(negative control of liver fibrosis group),olive oil + psychological stress group,liver fibrosis group,liver fibrosis + psychological stress group.Rats were given 40% carbon tetrachloride subcutaneous injection(3ml/kg,twice per week,double the first dose)for 8 weeks to establish liver fibrosis model,and olive oil was injected subcutaneously as negative control.A chronic psychological stress model was built using 10 unpredictable stimuli given randomly and differently daily for 4 weeks from the 5th week.The rats were killed at the end of the 8th week after the model was established.The portal vein blood was taken to detect the expression level of lipopolysaccharide(LPS)by spectrophotometry.The small intestine tissues were taken to evaluate the extent of intestinal mucosal lesions after hematoxylin-eosin staining.Immunohistochemical method was used to detect the expression of corticotropin-releasing hormone receptor 1(CRFR1)and occludin protein in small intestine.The liver tissue was taken to evaluate the degree of liver fibrosis after Masson dyeing.Results1.The semi-quantitative expression of CRFR1 protein in intestinal tissue showed that the expression of CRFR1 protein was gradually increased in the group of psychological stress,olive oil + psychological stress,liver fibrosis + psychological stress,and were higher than their negative control group respectively(P<0.001).The expression of CRFR1 protein in liver fibrosis group was significantly increased compared with the normal group and olive oil group,which increased further after chronic psychological stress stimulation(P < 0.001).2.The semi-quantitative expression of the occludin protein in intestinal tissue showed that the expression of occludin protein in psychological stress group,olive oil+psychological stress group and liver fibrosis+psychological stress group were lower than that in their negative control group respectively(p < 0.05).The expression of occludin protein in liver fibrosis group was significantly decreased compared with the normal group and olive oil group,which decreased further after chronic psychological stress stimulation(p < 0.05).3.The evaluation of intestinal mucosal lesions showed that:(1)The intestinal villi of the liver fibrosis group became shorter and thicker than that of the normal group and the olive oil group.The degree of intestinal villus atrophy was further deepened after psychological stress stimulation,which tended to be shorter and thinner(p<0.05).(2)The intestinal mucosal injury index of liver fibrosis group was higher than that of olive oil group and normal group,which increased further after psychological stress stimulation(p<0.05).4.The evaluation of the LPS level in portal vein showed that the expression of LPS in liver fibrosis rats was significantly higher than that in normal group and olive oil group,which increased further after psychological stress stimulation(p < 0.05).5.The staging of the liver fibrosis showed that the fibrosis of liver fibrosis group was significantly more severe than that of normal group and olive oil group,and the degree of liver fibrosis was further increased after psychological stress stimulation(p < 0.05).Conclusion1.CRFR1 is a sensitive indicator for detecting psychological stress and can be used to assess the body’s response to psychological stress.2.Hepatic fibrosis rats are in a state of high sensitivity to psychological stress.3.Intestinal lesions caused by chronic psychological stress may play an important role in the process of chronic psychological stress aggravating the degree of liver fibrosis in rats with liver fibrosis.