Oat Fiber Alleviates Loperamide-Induced Constipation in Mice by Modulating Intestinal Barrier Function

Objective: To investigate the effects of oat fiber on animal constipation and elucidate its underlying mechanisms. Methods: Male BALB/c mice were randomly allocated into five groups: control group (CON), model control group (MODEL), low dose group (LOW), middle dose group (MIDDLE), high dose group (HIGH). Constipation was induced in the mice by intragastric administration of loperamide. Subsequently, the mice (except those in the CON and MODEL groups) were administered oat fiber intragastrically for 21 consecutive days. Results: Compared with the MODEL group, oat fiber significantly increased the number of fecal pellets, fecal wet weight, and fecal water content (p < 0.05), shortened the time to first black stool excretion (p < 0.05), and enhanced the small intestinal propulsion rate in constipated mice. Additionally, oat fiber significantly upregulated motilin (MTL) and gastrin (GAS) levels (p < 0.05), while downregulating vasoactive intestinal peptide (VIP) and somatostatin (SS) levels (p < 0.05). It also significantly reduced the transcription level of Aquaporin 8 (AQP8) (p < 0.05), effectively alleviating intestinal mucosal injury and immune inflammation. The relative expression levels of TNF-α and IL-1β were significantly decreased in the oat fiber group (p < 0.05). Gut microbiota analysis revealed that oat fiber increased both the abundance and diversity of gut microbiota in constipated mice. Specifically, oat fiber was found to enhance the relative abundance of Firmicutes while reducing that of Bacteroidetes. At the genus level, it promoted the proliferation of Lachnospiraceae_NK4A136_group and Roseburia. Conclusions: Oat fiber alleviates constipation in mice by modulating gastrointestinal regulatory peptides, gut microbiota, aquaporin and mitigating intestinal barrier damage and immune-inflammatory responses.