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GASTROINTESTINAL, HEPATIC, PULMONARY, AND RENAL

Barakol Extracted from Cassia siamea Stimulates Chloride Secretion in Rat Colon

Department of Physiology, Faculty of Medicine, Srinakharinwirot University, Bangkok, Thailand (C.D., W.T.); Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand (S.P.); and Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand (N.K.)

Barakol is a purified extract of Cassia siamea, a plant that has been used as a laxative in traditional medicine. In this study, the effect of barakol on anion transport across the rat colon epithelium was investigated. Colonic epithelium was mounted in Ussing chambers and bathed with Ringer's solution. Addition of 1 mM barakol to the basolateral solution produced a slow increase in short-circuit current (Isc) in proximal colon and distal colon by 24.5 ± 2.2 and 24.2 ± 1.4 µA/cm², respectively. Barakol increased Isc in a concentration-dependent manner with an EC₅₀ value of 0.4 mM. The barakol-stimulated increase in Isc was inhibited by subsequent treatment with 500 µM diphenylamine-2-carboxylic acid or 400 µM glibenclamide added to the apical solution and 200 µM bumetanide added to the basolateral solution. Pretreatment of the tissues with 200 µM bumetanide, but not 10 µM amiloride, completely abolished the barakol-increased Isc. Ion substitution experiments showed an inhibition of barakol-stimulated Isc in chloride-free solution but not in bicarbonate-free solution. In addition, pretreatment of tissues with 10 µM tetrodotoxin or 10 µM indomethacin, but not 1 µM atropine or 10 µM hexamethonium, partially inhibited the Isc response by barakol. The present results demonstrated the stimulatory effect of barakol on the bumetanide-sensitive chloride secretion in rat colon. The effect of barakol was partly mediated by the stimulation of submucosal nerves and through the release of cyclooxygenase metabolites. These findings thus provide an explanation for the underlying mechanism of barakol as a secretagogue in mammalian colon.

Address correspondence to: Dr. Chatsri Deachapunya, Department of Physiology, Faculty of Medicine, Srinakharinwirot University, Sukhumvit 23, Wattana, Bangkok 10110, Thailand. E-mail address: chatsri{at}swu.ac.th