Several natural products containing
tannins are used as traditional medicines for treatment of
constipation; however, their pharmacological mechanism is not well understood. The
laxative effects of
gallotannin-enriched extract isolated from
Galla Rhois (GEGR) were investigated using a
constipation model induced by
loperamide (Lop) injection. After analysis for
antioxidant activity of GEGR, alterations in the excretion parameters, histological structure,
mucin secretion, and related
protein levels were measured in the transverse colon of Sprague Dawley (SD) rats with Lop-induced
constipation following treatment with 250, 500 and 1,000 mg/ml of GEGR. The number and weight of feces increased significantly by 48-79% and 128-159%, respectively, in the Lop+GEGR treated group relative to the Lop+vehicle treated group, while food intake and water consumption were maintained at a constant level. The thickness of mucosa, muscle and flat
luminal surface, as well as the number of goblet cells and crypt of lieberkuhn were enhanced in the Lop+GEGR treated group. Moreover,
mucin secretion increased significantly in a dose dependent manner in the Lop+GEGR treated group. Furthermore, the downstream signaling pathway of the
muscarinic acetylcholine receptors (mAChR) M2 and M3 was recovered by GEGR treatment, although the expression level varied. The levels of Gα expression and
inositol triphosphate (IP3) concentration were also recovered in the Lop+GEGR treated group relative to the Lop+vehicle treated group. The results of the present study provide strong evidence that
tannins distributed in various medicinal plants are important candidates for improving chronic
constipation induced by Lop treatment in animal models.