Inhibition of intestinal chloride secretion by proanthocyanidins from Guazuma ulmifolia

The antisecretory activity of Guazuma ulmifolia bark was examined in rabbit distal colon mounted in an Ussing chamber. Chloride secretion was stimulated by cholera toxin and prostaglandin E₂ (PGE₂). Guazuma ulmifolia extract (GUE) completely inhibited cholera toxin-induced secretion if the extract was added to the mucosal bath prior to the toxin. Adding the extract after administration of the toxin had no effect on secretion. GUE did not inhibit PGE₂-induced chloride secretion. These results indicate an indirect antisecretory mechanism. SDS-PAGE analysis of cholera toxin treated with GUE confirmed this presumption. GUE specifically interacted with the A subunit of the toxin. Preliminary phytochemical examinations showed that the most active fraction contains procyanidins with a degree of polymerisation higher than 8.