Objective:To discuss the method for establishing the rat models of irritable bowel syndrome(IBS)by chronic water avoidance stress(WAS)method,and to evaluate its feasibility.Methods:Thirty male Wistar rats were randomly divided into control group(n=10)and model group(n=20).The rats in model group were induced by WAS method for 1 h everyday,lasting for 10 consecutive days;the rats in control group underwent no interventions.After modeling,the general conditions and body weights of the rats in two groups were observed and recorded.The elevated plus maze(EPM)test was used to detect the percentages of the number of open arm entries(OE)and the time spent in open arms(OT)of the rats in two groups;the abdominal withdrawal reflex(AWR)test was used to assess the visceral sensitivity of the rats in two groups;electrocardiography was used to detect the heart rate variability(HRV)of the rats in two groups;electromyography(EMG)of the external oblique muscle was used to detect the colorectal pain sensitivity thresholds of the rats in two groups;multi-channel physiological signal recorder was used to monitor the slow wave frequency of the colon of the rats in two groups.Results:There were no death rats in both groups during the modeling period.After modeling,the rats in model group exhibited poor mental status,reduced spontaneous activity,hypoactivity,disordered and dull fur,irritability,and unclean anal areas;whereas,the rats in control group showed no significant changes in the mental state,spontaneous activity,fur,and perianal area.Compared with control group,the body weight of the rats in model group was significantly decreased(P<0.05).The EPM test results showed that compared with control group,the OE percentage and OT percentage of the rats in model group were significantly decreased(P<0.01).The AWR test results showed that 12 rats in model group scored≥3 points,indicating that the successful rate in creating the visceral pain models was 60%.Compared with control group,the low frequency(LF)signals and the ratio of LF/high frequency(HF)of the rats in model group were significantly increased(P<0.01),and the HF was significantly decreased(P<0.05).The EMG results showed that compared with control group,the coloretal pain sensitivity threshold of the colon of the rats in model group was significantly decreased(P<0.01),and the slow wave frequency of the colon was significantly increased(P<0.01).Conclusion:The WAS method for establishing the rat model of IBS effectively demonstrates the changes in behavior and mental state,increased the visceral sensitivity,accelerated colonic slow wave frequency,and autonomic nervous system imbalance;the WAS method can serve as an effective modeling approach for observing and evaluating the related drugs and interventions on treatment of IBS.

ObjectiveTo investigate the effect of Glycyrrhizae Radix et Rhizoma （GR）-containing serum on lipopolysaccharide （LPS）-induced inflammation in human colon epithelial adenocarcinoma cells （Caco2） based on inhibition of ferroptosis by the nuclear factor erythroid 2-related factor 2 （Nrf2）/heme oxygenase-1 （HO-1） pathway. MethodCaco2 cells were divided into a normal group， a model group （LPS， 200 μg·L^-1）， low-， medium-， and high-dose GR-containing serum groups （5%， 10%， 20%）， and a ferroptosis inhibitor group （3-amino-4-cyclohexylamino-benzoic acid ethyl ester， Fer-1， 10 μmol·L^-1）. The cells in the normal group were cultured normally， while those in other groups underwent the induction of an inflammation model. The cells in the low-， medium-， and high-dose GR-containing serum groups were treated with 5%， 10%， and 20% GR-containing serum for 24 hours， respectively， and the cells in the ferroptosis inhibitor group were treated with Fer-1 for 24 hours. Transmission electron microscopy was used to observe mitochondrial morphology in each group. Flow cytometry was used to detect intracellular Fe²⁺ levels. Microplate assays were performed to measure superoxide dismutase （SOD） activity， malondialdehyde （MDA） and glutathione peroxidase （GSH-Px） levels. Enzyme-linked immunosorbent assay （ELISA） was used to measure interleukin-1β （IL-1β）， IL-6， IL-10， and tumor necrosis factor-α （TNF-α） levels. Western blot was used to measure the expression levels of Nrf2， HO-1， ferritin heavy chain 1 （FTH1）， and glutathione peroxidase 4 （GSH-Px4） proteins. Small interfering RNA （siRNA） was used to investigate the role of Nrf2 in ferroptosis regulation. The cells after interference were divided into a negative control （NC） group， a Si-Nrf2 group， a GR-containing serum （20%） + Si-Nrf2 group， and a GR-containing serum （20%） + NC group. Microplate assays were performed to measure MDA， SOD， and GSH-Px levels， and Western blot was used to measure the expression levels of Nrf2， HO-1， FTH1， and GSH-Px4 proteins. ResultCompared with the normal group， the model group showed mitochondrial contraction， increased mitochondrial membrane thickness， and smaller mitochondrial morphology， increased Fe²⁺ content （P<0.01）， blunted SOD activity （P<0.01）， decreased GSH-Px expression （P<0.01）， increased MDA content （P<0.01）， reduced expression levels of Nrf2 and HO-1 （P<0.05）， reduced FTH1 expression （P<0.01）， and down-regulated GSH-Px4 expression （P<0.01）. In the GR-containing serum groups， the medium- and high-dose groups showed a significant decrease in Fe²⁺ content （P<0.01）， potentiated SOD and GSH-Px activities （P<0.01）， and decreased MDA levels （P<0.01）. The high-dose group showed a significant increase in Nrf2 expression （P<0.05）， and the medium-dose group showed increased expression of HO-1 and GSH-Px4 proteins （P<0.05）. The expression levels of FTH1 significantly increased in the low-， medium-， and high-dose groups （P<0.01）. The study on mechanism revealed that compared with the NC group， the cells transfected with Nrf2 siRNA showed increased MDA content （P<0.01）， blunted SOD activity （P<0.01）， decreased GSH-Px activity （P<0.01）， decreased expression of Nrf2 and HO-1 （P<0.01）， and reduced levels of FTH1 and GSH-Px4 proteins （P<0.01）. Compared with the Si-Nrf2 group， the cells treated with GR-containing serum showed a decrease in MDA content （P<0.01）， an increase in SOD activity （P<0.01）， an increase in GSH-Px activity （P<0.01）， increased expression of Nrf2 and FTH1 proteins （P<0.05）， and higher expression levels of HO-1 and GSH-Px4 proteins （P<0.01）. ConclusionGR-containing serum can reduce the inflammatory cytokines and oxidative stress levels in LPS-induced Caco2 cells. Its mechanism is related to the promotion of Nrf2/HO-1 signaling pathway expression， alleviating intracellular lipid peroxidation and inhibiting ferroptosis.