Changes in intestinal cell proliferation, absorptive capacity and structure in young, adult and old rats.

Intestinal epithelial morphology, crypt cell production and absorptive function were investigated in 9 groups of rats, aged from 3 to 121 weeks. Absorption per unit length of intestine peaked in the first weeks of life and this was associated with increased villus size, crypt length and absorption per mg tissue weight. Absorption per gut continued to increase throughout life, which could be attributed to a similar increase in intestinal length and weight per cm, despite a decreased absorption per mg in the adult animals. Crypt-villus ratio increased rapidly between 6 and 8 weeks, but then appeared to reach a plateau. Crypt cell production started off at high rate in all sites and then decreased in the young adult. While there was some evidence for a small, non-significant, increase in proliferation in the very old rats, there was no evidence of the marked elevation reported by some workers.