Changes in Ultrastructure of Duodenal Crypts in X-Irradiated Mice

Abstract

Four types of cells are found in the epithelium of the small intestinal crypts of mice. The great majority of them are principal or stem cells. The other three types are: mucous cells, possibly derived from stem cells; Paneth cells, which are secretory elements located at the bottom of the crypts; and Kultchisky cells. The epithelial cells lining the small intestine undergo continuous renewal (1). In the normal animal, dividing cells are restricted to the crypts. The total proliferative cycle of the stem cells is approximatively 12 hours, and about 14 hours elapses between the last division of a proliferative cell and their appearance in the villus. The functional cells migrate from the neck of the crypts to the tips of the villi where they are sloughed off into the lumen. The transit time within the villi can be estimated to be about 1 to 2.5 days. The small intestine of mice is known to be a very radiosensitive organ (2). Microscope studies have shown that mitotic activity is abolished in stem cells shortly after a supralethal dose of X-irradiation (3). After such a dose, there is some evidence indicating that during a few hours the cell cycle is slowed down. The epithelium of the small intestine is an interesting material for the study of changes in the ultrastructure of cells after X-irradiation--firstly, because of the presence in this epithelium of target cells with different radioresistance and, secondly, because of the possibility of following not only persisting damage to the irradiated cells themselves but also damage to the daughter cells. Some electronmicroscope studies on the irradiated intestinal epithelium already exist in the literature, but they are related to morphological changes and the disturbance of absorption occurring in the cells of the villi (4, 5). This study was undertaken in order to investigate the changes in ultrastructure found in the crypt cells of the duodenum of mice during the first 24 hours after a supralethal dose of X-rays.