The stimulant cathartic, emodin, contracts the rat isolated ileum by triggering release of endogenous acetylcholine

Summary 1 Anthraquinone stimulant cathartics, such as emodin, are believed to increase the rate of contraction of ileum tissue in vitro via multiple mechanisms. The aim of this study was to probe the effects of emodin on acetylcholine (ACh)‐induced contraction of the rat isolated ileum preparation. 2 Ileal sections were incubated in Tyrode's solution and responses to methacholine, ACh and emodin obtained in the absence and presence of the muscarinic antagonist atropine and the choline uptake inhibitor hemicholinium (HC‐3). Depletion of endogenous ACh in the presence of HC‐3 was achieved by construction of an ACh dose–response curve, using exogenous ACh, prior to re‐testing the effects of emodin in the presence of HC‐3. 3 Emodin caused dose‐dependent tissue contraction that was abolished by inclusion of atropine (1 μm) in the buffer. Atropine (1 μm) antagonized the response caused by methacholine. 4 Incubation of tissues with HC‐3 (1 and 10 μm) reduced the maximum response caused by emodin by 45% and 71% respectively, but had no effect on ACh‐induced tissue contraction. 5 These data suggest that, emodin causes contraction of the ileum by triggering the release of endogenous ACh which acts on muscarinic receptors to cause contraction of the rat isolated ileum preparation.