The acetylated phenolic laxatives bisaeodyl and diphesatin become absorbable from the intestine and active, pharmacologically, after deacetylation. The cleavage of the acetyl groups is effeeted by an enzyme present in the intestinal lumen.
Diphesatin which is hardly soluble in water, is cleaved only to a small proportion, probably about 10%. Accordingly, the free phenolic compound is ten times more active as a laxative than the original acetylated compound. Bisacodyl, having a slightly better water solubility than diphesatin is deacetylated completely and thus its deacetylated derivative is only as active as bisacodyl itself. The acetyl compounds as such are, probably, neither absorbed nor active.
After absorption the compounds are re-excreted into the intestine partly, and partly eliminated by the kidney. Excretion of bisacodyl into the intestine is effeeted via the bile. Only after this does the compound become active in the colon. This is substantiated by the fact that ligating the bile duct or the ileum prevents the laxative effect regardless whether (deacetylated) bisacodyl has been given orally or intraperitoneally. As on the first passage through the intestine the deacetylated compound is absorbed, one has to conclude that after re-excretion it is present in the gut in another state which prevents enteral absorption. In this state it moves down the intestinal tract and reaches the colon by this way.
Another explanation of the experimental findings would be to assume t h a t bile is necessary for the laxative effect and that the ligatures would only prevent bile from reaching the colon. This explanation is, however, less likely as even with simultaneous application of bovine bile is bisacodyl, given by mouth, ineffective when the bile duct is ligated. Further, bisaeodyl on rectal application is active in patients with biliary obstruction and stimulates the isolated perfused (bile-free) colon of cats (Göring and Schaumann).