Sennosides

Sennoside A and B, the components of senna, are metabolized by gut bacteria into the active metabolite rheinanthrone DB13175. Rheinanthrone DB13175 appears to increase cyclooxegenase 2 (COX2) expression in macrophage cells leading to an increase in prostaglandin E2 (PGE2). This increase in PGE2 is associated with a decrease in aquaporin 3 expression in mucosal epithelial cells of the large intestine. A decrease in aquaporin 3 expression likely produces the laxative effect by restricting water reabsorption by the large intestine thereby increasing fecal water content. The exact mechanism by which rheinanthrone increases COX2 expression is unknown. Rheinanthrone DB13175 also stimulates peristalsis in the large intestine although the mechanism behind this effect is unknown. Rhein DB13174, another active metabolite is thought to excite submucosal acetylcholinergic neurons resulting in increased chloride and prostaglandin secretion. The movement of chloride ions into the large intestine would also help to draw water into the lumen.