Abstract
The turnover time of the mucosal epithelium in the small intestine(jejunum and ilium) and large interstine(cecum), and the cells in the lamina propria of the small intestine was investigated with the radioautography in mice at various times after single injection of $^3H$-thymidine. Twenty suckling mice were sacrified at each of the following time intervals after injection ; 2 hrs, 1, 3, 5. 7, 14 and 17 days. 1. The labeled index of the epithelial cells in the crypt and the villus of the small intestine averaged 98.7% and 1.3% at 2 hrs, 982% and 1.8% at 1 day, 18.7% and 81.3% at 3 days, 6.3% and 93.7% at 5 days, respectively. The labeled index of the epithelial cells of the crypt-base, the upper-crypt and the mucosal surface in the large intestine averaged 71.8%, 28.2% and 0% at 2 hrs, 45%. 54.2% and 0% at 1 day, 17.2%, 54.5% and 28.2% at 3 days, 10.2%, 32.4% and 57.4% at 5 days, respectively. This result suggested that the turnover time of all the epithelial cells migrating from crypts to villi in the direction of the villus tips was calculated to be less than 5 days, and also the longest turnover time was calculated to be no longer than 7 day. 2. The labeled index of the total cells in the lamina propria of the small intestine averaged 6.2-7% at 2 hrs to 5 days, 4.7% at 7 days 2.6% at 17 days and this index is tend to be decreased moderately at 7 days and severely at 17 days. So this result suggested that the turnover time of the cells with the shorter cycle duration in the lamina propria of the small intestine were less than 5 days and that of the cells with the longer cycle duration more than 17 days.