Role of dietary protein adaptation at weaning in the development of the rat gastrointestinal tract.

To evaluate the role of the quantitative adaptation in dietary protein at weaning in the growth and maturation of the rat gastrointestinal tract, we studied parameters of tissue mass, DNA synthesis, and enzyme activities in suckling pups weaned by day 17 to a semipurified synthetic, isocaloric diet that contained either 8 or 27% casein (controls). Rats of both groups were studied on days 21, 28, and 35 postpartum. On day 21, protein restriction had little effect on mean body weight, wet stomach and liver weight, gut length and colonic, jejunal or ileal mucosal weights per centimeter, whereas on day 35, all these tissue mass parameters were significantly (p less than 0.01 versus controls) depressed in the 8% protein group. DNA and protein content expressed per intestinal segment or per total organ and the protein/DNA ratio paralleled the changes in tissue mass, except that total DNA of the small intestine was decreased by 33% (p less than 0.01 versus controls) in 21-day-old rats with protein restriction. In the same age group, DNA synthesis rate, measured by the incorporation rate of [3H]-thymidine per milligram tissue DNA, was markedly depressed in the small intestine (4-fold decrease; p less than 0.001 versus controls) and in the liver (2-fold decrease; p less than 0.05 versus controls) while in the colon the effect of protein restriction occurred later (day 35).(ABSTRACT TRUNCATED AT 250 WORDS)