Opioid-induced constipation (OIC) represents a prevalent adverse effect of opioid analgesics, affecting 60–90% of patients and significantly compromising quality of life. This review delineates the multifactorial pathogenesis of OIC. Peripheral μ-opioid receptor (MOR) activation suppresses enteric neuronal excitability, inhibits intestinal motility and secretion, and impairs rectoanal function. Notably, the colon appears to exhibit a distinctive lack of tolerance to opioids. Enteric glial cell activation has been implicated in neuroinflammation, while interstitial cells of Cajal show impaired pacemaker function. Central mechanisms are increasingly recognized to involve the brain–gut axis. Furthermore, opioid-induced barrier disruption, microbiota dysbiosis, and LPS/TLR4-mediated inflammation are proposed to interact and may contribute to a self-reinforcing cycle. Animal models have been instrumental in dissecting these mechanisms. However, they present limitations in reproducibility, clinical phenotype fidelity, and translational validity, particularly regarding microbiome composition and neuroimmune responses. Future research should prioritize the development of standardized, physiologically relevant animal models incorporating multi-omics approaches, and validate mechanism-based therapeutic strategies, including peripherally acting MOR antagonists and microbiota-targeted interventions, for precision management of OIC.

Background: The steady-state intestinal perfusion system represents a tool used in measuring intestinal fluid absorption and bicarbonate secretion in vivo; however, detailed procedures and parameters were not elucidated fully.Aim: We focused on the methods of the steady-state intestinal perfusion system comprehensively including the blood pressure, hematocrit, blood gas, and heart rate of mouse.Methods: Anesthetized, tracheally intubated, and artificially ventilated mice were used for this system. The blood pressure, hematocrit, blood gas, heart rate, and rate of fluid absorption and HCO₃^- secretion of the small intestine and colon at different time points were evaluated.Results: Blood pressure, hematocrit, blood gas, and heart rate became stable at the 30 min time point after completion of surgery and could be maintained for 2 h. Rates of fluid absorption and bicarbonate secretion were also kept stable during the period of steady state of mice. Rates of fluid absorption and bicarbonate secretion were different among the jejunum, ileum, proximal, and mid-distal colon.Conclusion: The steady-state intestinal perfusion system is a reliable system for measuring intestinal fluid absorption and bicarbonate secretion in vivo.

Abnormal intestinal mucosal immunity plays a crucial role in ulcerative colitis (UC). Autotaxin (ATX) can promote T cell migration and was reported to have a regulatory effect on Th17 cells, while sphingosine-1-phosphate (S1P) and its receptors (S1PRs) modulate Th17/Treg balance and inflammation, with S1PR modulators approved for UC. ATX can catalyze sphingosylphosphorylcholine (SPC) to produce S1P; however, the relationship between ATX and S1P/S1PRs in UC is unclear. Understanding the role of ATX-S1P/S1PRs in intestinal immunity can provide new treatment strategies for intestinal inflammatory diseases. Both UC patients and DSS-induced colitic mice showed significantly increased levels of ATX and S1P compared with healthy controls. ATX inhibitor PF8380 treatment led to reduced levels of S1P/S1PRs in colitic mice. Consistent with this, the S1PR antagonist etrasimod was able to alleviate ATX-induced intestinal inflammation, as well as partially restore ATX-induced Th17/Treg imbalance in MLNs and the spleen. In HT-29 and Raw246.7 cells, ATX treatment led to enhanced expression of S1P/S1PRs, with S1PR1 being the most significant. Furthermore, S1PR1 mediates the effect of ATX on Th17/Treg cell differentiation and function in vivo. Therefore, ATX affects the differentiation and function of Th17/Treg cells through S1P/S1PR1 signaling, increased ATX expression leading to Th17/Treg cell imbalance, intestinal mucosal immune dysfunction, and exacerbating intestinal inflammation.