DNAsynthesis and cell renewal in small and large intestines of mouse

DNA synthesis and cell renewal of mouse intestinal epithelium were studied with radioautography after injection of thymidine-H³ to know the difference of the mode of epithelial cell generation relating to the different frequency of cancer developement in several parts of small and large intestines. Succinic dehydrogensase activity was also observed by histochemical method. Renewal time of the intestinal epithelium of mouse is about three days throughout the intestine with somewhat longer time in rectum and anus, and relatively shorter one in ileum compared to the other parts of the intestine. Daily regenerating rate was low in large intestine, especially in rectum and anus. Strong activity of succinic dehydrogenase appeared in the bottom of crypt and seems to be correlated to the active cell division. Epithelial cells in large intestine move very slowly upward and few of them seem to move to the opposite side or stay long time at one place. Intermitotic time is about 27 hours in small intestine and about 40 hours in large intestine. These suggest some relations between the mode of the epthelial cell renewal and cancer development. Because in human the frequency of cancer development is very high in large intestine, rectum and anus, and the epithelial renewal of these areas is supposed to be delayed similarly as in mice.