Initial kinetic changes of prostaglandin E2-induced hyperplasia of the rat small intestinal epithelium occur in the villous compartments

This study was performed to further identify the sequence of cell kinetics that occurs in the development of gastric and intestinal epithelial hyperplasia after orally administered prostaglandins of the E series. A high-dose, short-treatment schedule was used to examine the initial effects on kinetic parameters in the rat small intestinal epithelium. Groups of rats were killed after a single dose of oral prostaglandin E2 at 1 h after in vivo labeling with methyl-3H]thymidine and during continued treatment at 6, 12, 24, 48, 72, and 96 h. As evidenced by autoradiography, the earliest change produced by prostaglandin E2 was an increased cellularity of the villous compartment (p less than 0.05 after 24 h). There was no change of labeling index of the villous compartment or of the leading edge of labeled cells within 24 h. At 48 h, the increased cellularity was accompanied by a significantly elevated labeling index of the villi. Throughout the study period no significant differences were observed between groups in the number of cells or labeling indices in the jejunal crypts, or in cellular input from the crypts to the villi. Epithelial turnover time in the placebo and treatment groups was 69 and 71 h, respectively. To exclude the possibility that prostaglandin E2 initially affects cell birth rate and mean cell cycle time, a metaphase blocker was given after 4 days of treatment in a second study. Animals were killed after 0, 0.5, 1.0, 1.5, and 2.5 h. The rate of entry into mitoses was 8.1% cells/h in controls compared with 8.2% cells/h in treated rats. The distribution of mitoses within crypts was identical in the two groups and the mean cell cycle time was 13.6 and 13.2 h, respectively. Also in this study there were trophic changes of the villi. It is concluded that the hyperplasia produced by oral prostaglandin E2 starts in the villi of the small intestine and is initiated by reduced cell exfoliation from the villous tips. Previously recorded retention of cellular elements in villi and crypts, increased cellularity of the proliferative compartments, and reduced mitotic index are secondary events.