- Prostaglandin E2-mediated stimulation of mucus synthesis and secretion by rhein anthrone, the active metabolite of sennosides A and B, in the mouse colon. Yagi, T., Miyawaki, Y., Nishikawa, A., Horiyama, S., Yamauchi, K., Kuwano, S. J. Pharm. Pharmacol. (1990)