Intestinal growth and adaptation in growing animals : the effect of age, luminal nutrition, growth factors and antigen transport

After major intestinal resection in the suckling and the immature rat, the residual intestine undergoes a marked compensatory regeneration, accelerated mucosal maturation and functional adaptation. The regenera¬ tion includes increases in villus height, crypt depth, marked cellular hyperplasia and cellular hypertrophy. The accelerated maturation in¬ cludes early increases in sucrase activity, and the early appearance of effective exclusion of enterically presented antigenic bovine serum albumin. In the suckling rat, functional adaptation is characterized by increases in sucrase and lactase activity per centimeter and per cell. The cellular hypertrophy and the increased sucrase activity per cell are in distinct contrast to the decreased cell size, and the de¬ creased enzyme activity per cell, observed after intestinal resection in adult animals. Accelerated mucosal maturation may be partly respons¬ ible for both. The rise in lactase activity, however, represents a functional adaptation, because in weanling and weaned rats lactase activity per cell falls after enterectomy. When food is absent from the intestinal lumen, compensatory regen¬ eration is inhibited, normal maturation of structure and function fails to occur, and normal longitudinal and mucosal growth of the intestine are both reduced. Nevertheless, the short-term inhibition of the struc¬ tural and functional response to intestinal resection, brought about by 10 days of parenteral nutrition, is only temporary, and is reversed by the reintroduction of normal feeding. Salivary growth factors and gastrin do not aid in the compensatory response, and gastrin may even inhibit maturation of mucosal enzyme function. Growth factors present in breast milk, however, appear to accentuate compensatory villus growth after intestinal resection in suckling rats, and breast milk also appears to bring about further acceleration of mucosal maturation