The measurement of gastro-intestinal protein loss by means of I131-labelled protein

Measurement of gastrointestinal protein loss is one of the major problems in the investigation of both the normal physiological leakage of plasma protein into the gastrointestinal tract and the abnormal loss in protein losing gastro-enteropathies. Protein loss in the alimentary tract cannot be measured in the stools, because the lost protein is digested and broken down into amino-acids which are re-absorbed. This paper outlines a search for an ideal labelled protein. This ideal would behave like endogenous protein after intravenous injection, would be not-toxic, easy to detect and measure and after passage into the gastrointestinal tract retain its label completely unabsorbed so that it can be measured in the stools. Finally, after degradation, wherever that takes place, the protein label would not be able to pass from the blood to the gastrointestinal tract. 2 figs, 1 tab