Intestinal absorption and excretion of thallium (201Tl) in the rat

The gastrointestinal transport of 201Tl-labelled monovalent thallium has been studied in normal and rats with cannulated bile ducts using an in vivo ligated loop technique. A marked difference in the Tl absorptive capacity among the various sections of the gut was observed. 201Tl was taken up more quickly from the colon than from any other segment and the uptake from the ileum and jejunum was higher than from the stomach. In addition, considerable amounts of the intravenously administered thallium were excreted into the intestinal lumen. The biliary excretion was very low compared with the direct transfer of 201Tl across the gastrointestinal wall that occurred against a tissue-to-plasma concentration gradient. In the rat, the large intestine seems to be the major area for the enteral reabsorption and recycling of thallium (I) ions.