CELL PROLIFERATION KINETICS IN THE GASTROINTESTINAL TRACT OF MAN. I. CELL RENEWAL IN COLON AND RECTUM.

In studies of cell proliferation in the intestine of animals during the past few years, observations have been made that suggest points of interest concerning cell renewal in humans. In rodents, proliferating jejunal and colonic epithelial cells have mean generation times of about 12 to 18 hours, DNA synthesis (S phase) times of 5 to 8 hours, and premitosis (G2) and mitosis (M) times of 1 to 2 hours (1-3). Also, although many epithelial cells undergo a second generation cycle soon after mitosis, some cells appear to remain longer in interphase before dividing again (3). The rate of disappearance of labeled cells from the mucosa has also been shown to vary in different portions of the gastrointestinal tract in a number of species; e.g., more labeled cells are present in the colon and stomach 1 week after injection of H3-thymidine than in the duodenum or jejunum (4). In man, studies of mitotic indexes and radioautographic studies with H3-thymidine have suggested turnover times of intestinal epithelial cells in the order of several days (5-7). In the present study, we have measured the mean generation time and the phases of the proliferative cycle of human colonic and rectal epithelial cells after the administration of H3-thymidine. The results describe cell renewal and give data on the rate of disappearance of labeled cells from the mucosa of the human colon and rectum.