RESUMEN
BACKGROUND: Animal studies show that Catha edulis inhibits gastrointestinal tract motility. However, there is little or no information on its effect on colon motility and the mechanism of action and active constituents responsible for this effect. This study therefore attempted to discern the effect, suggest the mechanism, and identify the active compounds from the crude extract. METHODS: A crude extract of Catha edulis was fractionated and subfractionated using column chromatography and HPLC. The activity of all fractions and subfractions was evaluated on rat colon longitudinal muscle. Nuclear magnetic resonance (NMR) spectroscopic data elucidations were used to identify the active compounds. An ileal segment preparation was used to investigate the possible mechanism of action. RESULTS: The crude extract of Catha edulis (0.05-0.5 mg/mL) inhibited spontaneous contraction of rat colon and ileum (P < 0.05), and tetrodotoxin (TTX, 10 µmol/L) failed to block this effect. Similar to verapamil (0.01-0.1 µmol/L), the Catha edulis extract (0.05-0.5 mg/mL) inhibited high K+ (80 mmol/L)-induced sustained ileal contraction and decreased the response to Ca2+ . Analysis of the NMR data showed that quercetin, kaempferol, and myricetin were the active phytochemicals. All the identified compounds were flavonoids and significantly inhibited (P < 0.05) spontaneous contraction of the rat colon longitudinal muscle compared to controls. CONCLUSIONS: The crude extract of Catha edulis has a spasmolytic effect on the rat ileum, which is mediated through blocking Ca2+ channels, and quercetin, kaempferol, and myricetin were found to be the causative compounds.