INTESTINAL ABSORPTION OF SIX TRITIUM-LABELED DIGITALIS GLYCOSIDES IN RATS AND GUINEA PIGS

¹ Division of Gastroenterology, Department of Medicine; Department of Pharmacology, Ohio State University College of Medicine, Columbus, Ohio

Relatively little attention has been directed toward the mechanism of the intestinal absorption of digitalis glycosides. In the present investigation the absorption of six tritium-labeled cardiac glycosides was studied in rats and guinea pigs utilizing isolated intestinal loops in vivo and everted duodenal and jejunal gut sacs in vitro. The nonpolar glycosides, digitoxin, digoxin and proscillaridin, were found to be absorbed more rapidly than the polar glycosides, ouabain, dihydroouabain and convallatoxol. Bile duct ligation did not affect the absorption of digitoxin from isolated intestinal loops in rats. The absorption of digitoxin was directly proportional to substrate concentration both in vivo and in vitro. In in vitro studies the transport of digitoxin was not affected by the presence of several metabolic inhibitors (dinitrophenol, iodoacetate, sodium azide), by the omission of glucose from the incubation medium or by anaerobic incubation conditions, indicating that the transport of digitoxin does not depend upon energy supplied by cellular metabolism. In addition, the transport of digitoxin was not inhibited by another cardiac glycoside, digoxin, suggesting that there are no specific transport sites that allow for competition between glycosides. These observations indicate that digitoxin is absorbed by a passive (nonsaturable) transport process.