De-iodination of labelled protein during intestinal transmission in the suckling rat

Oral feeding of [125I] diiodotyrosine (125DIT) to young rats resulted in a rapid de-iodination of a large proportion of the fed dose. There was no significant incorporation of 125DIT, or inorganic iodide 125I, into protein during transmission across the intestine. Radioactive iodide was the major iodinated metabolite when 125I-labelled bovine albumin or 125I-labelled bovine IgG were fed to young rats, and a large proportion of this iodide was secreted into the stomach during the course of the experiment. Discrepancies have been found in the values of the concentrations of iodinated bovine IgG reaching the circulation when these have been compared by isotopic and immunochemical assay. The lower values observed for the isotopic c. q. s , were assumed to be a resultant of the de-iodination of the iodinated protein during gut transfer.