Age effect on cell-transit time in mouse jejunal epithelium.

FRY, R. J, M., S. LESHER, AND H. I. KOHN. Age effect on cell-transit time in mouse jejunal e$Ywlium. Am. J. Physiol. 20 I (I ) : 213-216. I g6r .Epithelial cell renewal in the jejunum of CAFr mice was studied by observing the time for cells labeled with tritiated thymidine (1.5-2.0 PC/g body wt.) to pass from the crypt to the extrusion zone at the tip of the villus. Mice of three ages were studied : 93, 372, and g4o days. The total observed transit times were 44, 52, and 53 hr, respectively. The increase with age was the result of increase in both the crypt and villus transit times. Structural changes could not be made to account for the differences. The increase may be the result of a decreased rate of cell production in the crypts. The jejunum was taken from young (0.25 yr), middleaged (I yr), and old (2.6 yr) mice. The expected survival of the normal CAFl mouse at these ages is IOO %, g8%, and about 25%, respectively. Three series of animals were studied : series A (r g58), which supplied the material for the previous study of the duodenum (I), and two later ones (B, 1959; C, 1960). The numbers of animals from each series assigned to the various age groups, average weights and tumor incidences, and the times of sacrifice, are given in Tables I and 2.