Antidiarrheal activity and acute oral toxicity of Mentha longifolia L. essential oil

OBJECTIVES: Mentha longifolia L. (Lamiaceae) is an annual herb that is used in the Iranian traditional medicine for treating stomach and intestinal disorders. The purpose of this study was to determine the protective effect of M. longifolia on experimental diarrhea in a rat model. MATERIALS AND METHODS: The antidiarrheal activity of essential oil of M. longifolia (20-80 mg/kg) was investigated against castor oil-induced diarrhea in rats using loperamide as the standard reference drug. In acute toxicity evaluation, rats were orally administrated with single dose of EOML at doses ranging from 10 to 1000 mg/kg. RESULTS: EOML caused a significant (p<0.05) and dose-dependent decrease of gastrointestinal transit, nevertheless, it could not block the inhibitory effect of atropine (0.1 mg/kg). EOML at oral doses of 20 and 80 mg/kg protected the animals against castor oil-induced diarrhea significantly (p<0.05). EOML decreased the intestinal fluid accumulation as indicated by the significantly (p<0.05 to p<0.001) decrease compared to control. The oral LD(50) of EOML was found to be 470 mg/kg in rat. CONCLUSION: Since the inhibition of intestinal hyperactivity and hypersecretory are the bases of the treatment of diarrhea, results obtained in the present study suggest that EOML is endowed with antidiarrheal activity. EOML is moderately toxic for oral medication.