Toxicity Studies On Tannic Acid Administered By Enema .2. Colonic Absorption And Intraperitoneal Toxicity Of Tannic Acid And Its Hydrolytic Products In Rats

ration for roentgenologic examination or after incorporation in the barium enema. Since gastrointestinal absorption must have preceded hepatotoxicity, the condi- tions necessary for absorption are of inter- est. Unfortunately, absorption from the gastrointestinal tract has been poorly de- fined, largely due to the lack of adequate methods to detect intact tannic acid in biologic fluids and to distinguish it from the hydrolysis products, gallic acid, and related polyhydroxy acids. The effects of the route ofadministration, diet, or species and strain variability have not been established. The chemistry of (gallo-) tannic acid is well known.7 Although it is probably of heterogenous composition, there is no doubt that it is a large, complex glucosidic polyester of gallic acid and related phenolic acids. The molecular weight has been pro- posed to be in the range of 1,500 to 2,000. It reacts to form precipitates with proteins, mucoproteins, alkaloids, and various cati- onic compounds. Further, being an ester, the compound is labile to hydrolysis in moderately alkaline solutions and also very easily hydrolyzed by esterases.7'8