The radiosensitivity of a mesenchymal tissue. The pericryptal fibroblast sheath in the human rectal mucosa.

With the exception of haemopoietic tissue quantitative studies of the effects of irradiation on replicating normal tissue call systems in vivo have previoulsy been confined to epitelial tissuss. A similar sheath of fibroblasts to that surrounding the crypts of Lieberkühn in the colon, which it is climed undergoes constant renewal and migration, has now been identified in the rectum and thereby it may become possible to follow the cellular response to irradiation of a mesenchymal tissue. The numbers and the distribution of the pericrytal fibroblasts in normal human rectum following irradiation, both in air and hyperbaric oxyge, have been stuided in serial biopsies of rectal mucosa taken from patients who were being treated for advanced pelvic maliganancies. The results indicate that during a course of irradiation the fibroblasts cell count falls on a time-scale very closely associated with that seen in the epithelial cells. Only some immediate recovery occurs in the fibroblast system, in contrast to the adjacent epithelial cell system where full recovery seems to take place. The fibroblast system, moreover, shows a gradually diminishing trend during the first year, whilst the epithelial cell numbers appear to be maintained. The interpretation of these data are discussed. Evidence is provided that when patients breath hyperbaric oxygen during irradiation more extensive depression of cell numbers occurs, but after recovery there is essentially no difference in the cell counts - finding that accord with those previously reported fro epithelial cells in the crypts of the rectal mucosa.