Cell proliferation of pericryptal fibroblasts in the rat colon mucosa.

The turnover of pericryptal fibroblasts in the rat colon mucosa was analysed after in vivo incorporation of tritiated thymidine. Thirty-six rats were serially killed one hour to 21 days after intraperitoneal injection of the radionuclide. At one hour, the labelling index of pericryptal fibroblasts was only 2.44%; labelled fibroblasts were slightly predominant along the lower two-thirds of the crypts. Within 24 hours, most underwent at least one cell division. No migration was observed and a significant proportion of labelled fibroblasts was still present after three weeks. It is concluded that those fibroblasts constitute a slowly renewing cell population. The data failed to confirm the hypothesis of an 'en bloc' migration of fibroblasts in synchrony with the epithelial cells.