Acceleration of large intestine transit time in rats by sennosides and related compounds

Sennosides A + B and their natural metabolites, sennidins A + B, rheinanthrone and rhein, as well as the synthetic laxative danthron, were investigated for their influence on small and large intestine transit time in rats. Carmine red, as a marker, was administered through a gastric tube for small intestine transit or intracaecally by a chronically implanted catheter for colon transit. High doses of sennosides (250-500 mg kg-1) given orally from 20 min or up to 6 h before marker administration had no effect on small intestine transit time. The metabolites and danthron (10-100 mg kg-1 p.o.) also did not accelerate upper gastrointestinal passage. Intracaecal administration at the same time as carmine red, however, reduced the time for the appearance of the first coloured faeces from more than 8 h in the controls to 46 +/- 9 min after sennosides, 34 +/- 11 min after sennidins, 53 +/- 83 min after rhein and 16 +/- 4 min after rheinanthrone (50 mg kg-1 of each). Danthron was ineffective. Thus, sennosides and their natural metabolites specifically influence large intestinal motility. Acceleration of colonic transport seems to be a major component of the laxative action whereas for danthron motility changes are not responsible for its laxative action. Indomethacin partly inhibited the acceleration of large intestine transit induced by sennosides. An involvement of endogenous prostaglandins may therefore be possible, although a local bolus administration of PGF2 alpha or PGE2 into the caecal lumen neither influenced transit time nor induced diarrhoea.