Vanillic acid reverses castor oil-induced diarrhea in BALB/c mice through cholinergic and calcium channel blocking effects

Background: Diarrhea is one of the leading cause of death in developing countries. The available pharmacotherapy is linked with adverse effects. Vanillic acid is the major constituent of Vanilla planifolia and Vanilla tahetensis which are used in complementary medicines for treatment in gastrointestinal irritations and spasms. Objectives: This study aimed to investigate the antidiarrheal effect of vanillic acid in castor oil-induced diarrhea in BALB/c mice. Methods: The effects of vanillic acid on the diarrheogenic activity, gastrointestinal transit (GIT) and intestinal fluid contents in BALB/c mice model were evaluated. Additionally, the possible role of nitric oxide (NO), prostaglandin E2 (PGE2), opioid and cholinergic pathways were also investigated. In-vivo experiments were performed for ratifying the cholinergic and calcium channel blocking effects of vanillic acid. Results: Various doses of vanillic acid (1, 3, 5, 7 and 10 mg/kg) showed 12.20%, 23.80%, 48%, 61.80% and 79.20% protection against castor oil induced diarrhea in mice and induced significant volume reduction in enteropooling test; 7.44%, 37.23%, 48.93%, 63.82% and 70.21%. Through atropine-sensitive effect it reduced the gastrointestinal transit by 49.82%, besides inhibiting PGE2-induced diarrhea by 39% at 10 mg/kg dose. In in-vitro studies it showed spasmolytic effects on jejunum contractions: spontaneous (EC50 value=0.21 µg/mL), high K+ (EC50 value=4.31 µg/mL) and carbachol-induced (EC50 value=0.25 µg/mL); and on ileum contractions: high K+ (EC50 value=2.34 µg/mL) and carbachol-induced (EC50 value=0.16 µg/mL). Calcium response curves produced a similar effects to verapamil. Vanillic acid was found safe in mice up to 2 g/kg body weight. Conclusion: It reduced intestinal transit stimulated by muscarinic agonist and intestinal secretion induced by PGE2. In-vitro experimental results showed vanillic acid's spasmolytic action on jejunum and ileum tissues, likely through VDCC inhibition and muscarinic receptor antagonism.