Laxative effect of ispaghula: physical or chemical effect?

Seed husk of Plantago ovata (ispaghula) is a popular laxative used to regulate bowel movements. It is generally believed that its laxative effect is mediated through its fibre and/or hydrophilic mucilloid contents. We demonstrate in this communication that it also contains active chemicals causing a laxative effect. An aqueous–methanol extract of ispaghula at a dose range of 1–10 mg/mL caused a dose‐dependent stimulatory effect in guinea‐pig ileum. Pretreatment of tissue with atropine (1 μ M ) completely blocked the contractile effect of a supra‐maximal dose of acetylcholine (10 μ M ) similar to that of the lower doses of ispaghula (1–4 mg/mL), however, the effect of the larger doses (6 and 10 mg/mL) was blocked partially. These results indicate that the stimulatory effect of ispaghula at lower doses is mediated through an ACh‐like mechanism and the effect of high doses was mediated partially through unknown mechanism(s). © 1998 John Wiley & Sons, Ltd.