Influence of chronic bisacodyl treatment on the effect of acute bisacodyl on water and electrolyte transport in the rat colon.

Excessive or unnecessary taking of laxatives leads to a vicious circle with perpetuation of laxative abuse and increase of laxative dosage, accompanied by severe clinically evident disturbances. It was investigated in rats whether chronic administration of bisacodyl reduces the effects of acute bisacodyl administration on net water and electrolyte flux in the rat colon transport in-vivo. After chronic pretreatment with bisacodyl had been given for 21 days (3 mg and 10 mg kg-1 day-1), net water and sodium absorption was found to be decreased whereas potassium secretion was increased. After 21 days of pretreatment, the effect of acute bisacodyl (10 micrograms ml-1 intraluminal) on net water and sodium transport was reduced whereas the effect on potassium secretion remained unchanged. Serum and erythrocyte levels of sodium and potassium remained unchanged in chronically pretreated rats. Serum aldosterone levels were enhanced two fold. It is concluded that under the experimental conditions described, chronically administered bisacodyl leads to elevated serum aldosterone which counteracts the effect of bisacodyl on net water and sodium transport but acts synergistically with bisacodyl on the effect on potassium loss.