The fate of a major biliary metabolite of digitoxin in the rat intestine.

In the rat, the major water-soluble biliary metabolite of digotoxin is digitoxigenin monodigitoxoside glucuronide (mono-gluc). Despite its preponderance in the bile, only small amounts of mono-gluc are found in the feces. The compound may be absorbed from the intestine as the glucuronide conjugate, or it may be hydrolyzed to the parent compound, digitoxigenin monodigitoxoside (mono); the parent compound might then be absorbed from the intestine. The purposes of this study were to determine the ability of closed duodenal and cecal strips in vivo to absorb the conjugate and the parent compound, to hydrolyze the glucuronide, and to conjugate the parent mono. Absorption of mono was found to be more rapid than mono-gluc in both intestinal locations. Absorption of mono in the cecal strip was slower than in the duodenal strip. Considerable hydrolysis of mono-gluc occurred in the cecal strip; in the duodenal strip, the net process was conjugated of the parent mono. Thus, the disappearance of mono-gluc between its appearance in the bile and excretion in the feces is explained mainly by hydrolysis in the lower intestinal tract. Paradoxically, absorption of the hydrolysis product, mono, proceeds more slowly in the lower intestine, where it is hydrolyzed, than in the duodenum, where hydrolysis does not occur.