Received for publication February 2, 2005.
Revised April 28, 2005.
Accepted for publication April 28, 2005.

Barakol Extracted from Cassia siamea Stimulates Chloride Secretion in Rat Colon

Abstract

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 solution. Addition of 1 mM barakol to the basolateral solution produced a slow increase in Isc in proximal colon and distal colon by 24.5 ± 2.2 µA/cm² 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 DPC 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 choride-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 stimulation of submucosal nerves and through the release of cyclooxygenase metabolites. These findings thus provide explanation for the underlying mechanism of barakol as a secretagogue in mammalian colon.

Key words: Barakol, Chloride secretion, Ion transport, Laxative, Rat colon, Ussing chamber