The effect of protein-deficient isoenergetic diets on the growth of rat jejunal mucosa.

1. Newly weaned 21-d-old male rats were given isoenergetic diets containing 200, 100 and 50 g protein/kg for 7, 14, 28 or 70 d. The mid-jejunum was removed from the rats and a micrometric analysis of the mucosa was made. The following measurements were made: number of villi/mm2, villus dimensions, villus surface area, crypt depth, crypt: villus, the number of cells/crypt in metaphase arrest per h. 2. Comparison were made between animals of the same age but on different diets, and animals on the same diet but of different ages. The latter comparison gave information on the effect of protein deficiency on the pattern of maturation of each feature of the villus or crypt studied. 3. The effect of protein deficiency was not consistent at each stage of maturation. For instance villus height was decreased when compared with the controls following 28 d on a protein-deficient diet but not after 7 or 70 d. 4. The only measurement to be unaffected by protein deficiency was the number of villi per unit area. 5. In general the 50 g protein/kg diet had a more pronounced effect than the 100 g protein/kg diet. Protein deficiency delayed maturation by either slowing or inhibiting changes seen in normal maturation. 6. In rats given 50 g protein/kg diet, although the villus surface area did not increase as the rats matured there were increases in epithelial cell production rate and number of crypts per villus.