Inhibition of intestinal water and electrolyte absorption by senna derivatives in rats

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Abstract
Three intestinal segments were simultaneously perfused with Tyrode solution in the anaesthetized rat using a perfusion rate of 12 ml h−1. Dried purified senna extract containing 60% Ca-sennosides A + B (I) administered with the perfusion fluid had no or only minimal effects on intestinal absorption. Large doses (4 g litre−1) slightly reduced net Na, CI and H2O absorption predominantly in the colon and the ileum; the jejunum was unaffected. Dried purified senna extract containing 18% oxidized Ca-sennosides (II) reduced net Na, Cl and H2O absorption in all three intestinal segments, the effects increasing from the jejunum to the colon. Large doses (4 g litre−1) induced net Na and H2O secretion. II being administered with the colon perfusion fluid affected H2O and electrolyte absorption in the colon and to a lesser degree, in the ileum. Pure rhein (III, 0·28 g litre−1) had similar effects to II. Pure sennosides A + B (IV, 2 g litre−1) had no effect on intestinal absorption. These results confirm that changes in the absorptive behaviour of the gut mucosa are, at least partly, responsible for the laxative action of anthraquinone drugs and that this effect is mainly dependent on the presence of oxidized derivatives. There is evidence that the drug's effect is not locally restricted to the colon as is seen from the ileal response after intracolonic administration. Side-effects like griping which are sometimes observed after senna treatment seem to originate from motility changes rather than from changes in absorption.