Exploring the Dose-Effect Relationship of Bifidobacterium longum in Relieving Loperamide Hydrochloride-Induced Constipation in Rats through Colon-Released Capsules.

Constipation is a common disease affecting humans. Bifidobacterium longum is reportedly effective in relieving constipation. Current studies generally focus on the dose-response relationship of oral doses; however, the dose-effect relationship of B. longum in the colon, which is the primary site where B. longum exerts constipation-relieving effects, to treat constipation has not been studied. Herein, three strains of B. longum (FGSZY6M4, FJSWXJ10M2, and FSDJN6M3) were packaged in colon-released capsules to explore the dose-effect relationship in the colon. For each strain, three groups of capsules (10 4 , 10 6 , and 10 8 CFU/capsule, respectively) and one group of free probiotics (10 8 CFU/mL) were used to explore the colonic dose effect of B. longum . The results showed that the three strains of B. longum improved fecal water content and promoted intestinal motility by regulating gastrointestinal peptide (MTL, GAS, and VIP), aquaporin-3, and 5-hydroxytryptamine levels while promoting gastrointestinal motility and relieving constipation by regulating the intestinal flora composition of constipated rats and changing their metabolite content (short-chain fatty acids). Among the three free bacterial solution groups (10 8 CFU/mL), FGSZY6M4 was the most effective in relieving constipation caused by loperamide hydrochloride in rats. The optimal effective dose of each strain was 6M4 (10 4 CFU/day), 10M2 (10 6 CFU/day), and S3 (10 8 CFU/day) of the colon-released capsules. Therefore, for some effective strains, the dose of oral probiotics can be reduced by colon-released capsules, and constipation can be relieved without administering a great number of bacterial solutions. Therefore, investigating the most effective dose of B. longum at the colon site can help to improve the efficiency of relieving constipation.