The application of 1,8-cineole, a terpenoid oxide present in medicinal plants, inhibits castor oil-induced diarrhea in rats.

1,8-Cineole, a terpene, characterized as a major constituent occurring in the essential oils of several aromatic plants. It is widely used in pharmaceutical industry, as a food additive and for culinary purposes. This study investigates the inhibitory effect of 1,8-cineole on transit time and diarrhea in animal models. Acute toxicity and lethality of 1-8-cineole was determined by Lork's guidelines. The antidiarrheal effect of 1,8-cineole was investigated by determining the intestinal transit and enterpooling in rats. In all experiments, different doses of 1,8-cineole (20-120 mg/kg), atropine, and loperamide were administered orally. The LD50 of 1,8-cineole for oral administration was estimated to be 1280 mg/kg. 1,8-Cineole (20-120 mg/kg) did not show a significant decrease in small intestine transit (p > 0.05); however, the highest dose displayed a significant decrease in comparison with atropine (p < 0.05). This substance decreased the peristaltic index value to 68 ± 0.36% at a dose of 120 mg/kg compared with the control group (85.22 ± 4.31%) in the castor oil transit test. 1,8-Cineole significantly delayed the onset of diarrhea to -142.33 ± 6.08 min at 120 mg/kg, while the time was 103.66 ± 20.73 min for the control and >240 min for the loperamide. Moreover, 1,8-cineole significantly decreased intestinal fluid accumulation (p < 0.05). This study demonstrated antispasmodic and antisecretory activities of 1,8-cineole and rationalized the traditional use of the plant containing various levels of this terpene in the treatment of gastrointestinal complains such as diarrhea.