The Cell Cycle Time in the Rat Jejunal Mucosa

The regional variation of the duration of cell cycle parameters was studied by constructing fraction of labelled mitoses curves at several levels in the jejunal crypt column of male Wistar rats. Prolonged T c and T s values were apparent only in the bottom eight cell positions, and these differences were shown to be significant compared with the remaining cell positions by analysing the data by the method of Gilbert (1972). Above cell position 8 the proliferating crypt cells showed effectively the same phase durations. For the whole crypt column T c was 11.32 ± 0.14 (SE) and T s 6.49 ± 0.10. Although variation in phase durations was confined to the basal portion of the crypt, the results essentially confirm the findings of Cairnie, Lamerton & Steel (1965a), and may be interpreted in terms of the slow cut‐off model. The demonstration of prolonged T c values in basal cell positions confirms the presence of a longer cycling subpopulation of cells at the bottom of the crypt.