Abstract

The effect of sodium rhein on contractile activity and fluid flow in the rat complete large intestine was studied in vitro. Contractile activity was recorded using serosal strain gauges and volume transducers recorded distal fluid flow from the segment. Luminal sodium rhein (1 mM) produced a protracted increase in caecal activity yet increased colonic contractility transiently. Fluid flow from the preparation was increased and the number of propagated complexes was elevated after the initial 10 min of exposure. The effect did not appear to be related directly to dose. Sodium rhein (0.1 mM) did not significantly stimulate contractility and a higher dose (5 mM) only produced a transient effect on propagated contractions. However, this dose had the effect of significantly reducing activity when the rhein was replaced by normal buffer. The data suggest that the action of sodium rhein is subtle; after an initial excitation, the glycoside shifts the pattern of motor activity in favour of propulsion at the expense of segmentation. The large intestine is more able, therefore, to expel luminal contents in a caudal direction following the addition of this anthraquinone laxative.