SOY FLOUR AND FECAL THYROXINE LOSS IN RATS

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Abstract
Rats fed soy flour and control diets were injected intravenously with tracer amounts of I131-labelled thyroxine. Counts of radioactivity in collections of feces and in blood samples over a 90-hour period, and final whole carcass counts, confirmed the previous report of increased fecal excretion of thyroxine in soyafed animals. In investigating the mechanism of this effect rats fed on control and soy flour diets were subjected to biliary drainage over 12 hours through a polythene tube inserted into the common bile duct following intravenous injection of labelled thyroxine. The proportions of the injected radioactivity excreted in the bile, and present terminally in the gut, were measured. Samples of bile and butanol extracts of feces were chromatographed and the nature of the radioactive compounds determined. No differences were found between control and experimental groups in any of these parameters. It was concluded that the excess thyroxine in the feces of soya-fed rats was not due to increased biliary secretion or to addition of thyroxine to the gut from any other source.