Sennoside-induced secretion and its relevance for the laxative effect.

The effect of oral treatment with sennosides (50 mg/kg) on the time-course of net H2O and electrolyte transport rates was studied in 1-hour incubation experiments in the rat colon in vivo. Net H2O, Na+ and Cl- absorption rates did not change during the first 4 h after treatment, but were reversed to net secretion after 6 h and partly recovered during the next 18 h. K+ and Ca2+ were secreted in controls, and net secretion increased from 6 to 24 h after treatment. Paracellular permeability of [14C]erythritol was 3-fold 6 h after treatment but unchanged at other times after treatment (2, 4, 12 or 24 h). LDH leakage into the lumen was not enhanced by treatment. Neither mucosal Na+, K(+)-ATPase activity nor cAMP or phosphodiesterase activity was affected by sennosides. As stool consistency and acceleration of transit by sennosides has entirely normalized 24 h after treatment but not net absorption of H2O and electrolytes, it is concluded that there may be regional differences in the absorptive behavior of the colon induced by sennosides. Slow transit and increased absorption in some parts of the colon may overcome secretion in other parts.