Protein loss and cell loss from the small-intestinal mucosa.

Total protein and deoxyribonucleic acid (dna) were measured in small-intestinal washings from rats with normal and high rates of dna (or cell) loss. There was a significant relationship between the loss of these two substances. Preparations of isolated viable epithelial cells contained much less protein in relation to dna than did the intestinal washings. It was calculated that only 8 to 15% of the protein lost by washing the rat small intestine arose from the intracellular protein of exfoliated epithelial cells. The rest was derived from extracellular sources.Protein and dna loss from small-bowel mucosa was measured in six patients. The ratio of protein to dna was similar to that found in the rats. The mean protein loss from 5 cm of human upper small intestine was 956 mug per min or 1.4 g per 24 hours. By calculation, total protein loss from the whole small intestine of man was about 84 g per day, about 10 g coming from within exfoliated cells and the rest arising from extracellular sources. The normal intestine must reabsorb most of this material.