Changes in upper intestinal epithelial morphology and kinetics in the growing guinea pig.

Weaning, the process of intestinal adaptation from milk to solid diet, demands changes in gastrointestinal function. We aimed to measure upper intestinal mucosal morphology and cytokinetics during early life, to determine whether the marked changes seen at weaning in altricial species, such as rat and mouse also occur in the precocial guinea pig. A total of 79 animals was studied. Jejunal morphology was measured by microdissection and crypt cell production rate by a metaphase arrest technique in animals at 1, 7, 14, 21, and 28 days after birth. There was a 40% decline in villus height from 986 to 576 microns during the first 2 wk (p less than 0.001). Crypt depth increased by 25% from 148 to 199 microns (p less than 0.01). After an initial decline there was a significant increase in crypt:villus ratio from 6.7 to 8.2 (p less than 0.001), in crypt cell production rate from 3.9 to 5.6 cells/crypt/h (p less than 0.001), and net villus influx from 26.1 to 45.9 cells/villus/h (p less than 0.001) from 14 days onward. These proliferative changes were accounted for by an increase in the depth and number of crypts, and in crypt cell production rate, leading to an increase in net villus influx. In contrast with the rat and mouse they were gradual, occurred largely during the 3rd wk, and appeared to follow the cessation of breast feeding and commencement of solid food. It is suggested that the functional changes in the small intestine that occur during weaning in the guinea pig are neither due to rapid proliferation of a new epithelial cell population, nor precipitated by change in diet.