Effect of sennosides on colon motility in dogs.

Oral administration of sennosides (20-30 mg/kg) to fasted dogs has been shown to induce a strong and long-lasting inhibition of myoelectric colon activity which was evident after a delay of 6-10 h corresponding to oro-cecal transit and colonic metabolism and was accompanied by abundant diarrhea. When sennosides were given 1 h before a meal, the postprandial increase in colon motility failed to appear. Recent studies with strain gage transducers confirm the inhibition of colonic motility after oral sennosides but, in addition, 3-10 'giant contractions' with a high amplitude appeared during the period of inhibition. Most of these single contractions were propagated over the second half of the colon at a velocity of 0.5-2 cm/min. Elimination of liquid feces was always associated with giant contractions. These giant contractions have also been described with other stimuli (i.v. guanethidine or neostigmine, oral castor oil, intraluminal hypertonic glucose) and are therefore not specific for sennosides.