The effect of cathartic agents on transmucosal electrical potential difference in the human rectum

Active ion transport in the colon is generating a transmucosal electrical potential difference (PD) of about 40 mV. Cathartic agents inhibit electrolyte and water net-absorption or cause net-secretion which should be reflected in a change of PD. In 83 normal subjects the effect of an isotonic eletrolyte solution (control) and different cathartic agents on rectal PD was tested: Laxatives (bisacodyl, rhein), bile acids (cholic and deoxycholic acid), fatty acids (oleic and ricinoleic acid) and cardiac glycosides (meproscillarin, digitoxin, digoxin). Bisacodyl, deoxycholic acid in high concentration, meproscillarin and digitoxin significantly decreased PD, while the other substances did not. Cathartics act on different transport mechanisms which together with different absorption characteristics of the proximal and distal colon may explain the difference in effecting the PD. Rectal PD measurement provides an easy and convenient tool to document effects of cathartic agents on electrolyte transport, otherwise difficult to obtain, and is applicable for clinical use.