Late radiation response of kidney assayed by tubule-cell survival

An assay for the survival of renal tubule cells was developed using mice. It is analogous to other in-situ clonogenic cell survival assays. One kidney was irradiated using a ¹³⁷Cs irradiator and removed 60-68 weeks later for histological examination. In unirradiated animals there were about 370 tubules in contact with the capsule in a coronal cross section at the middle of the kidney. After irradiation, extensive tubular damage was the dominant lesion. The number of epithelialised tubules in contact with the capsule showed a dose-dependent logarithmic decline. The dose-survival relationship for the clonogenic cells responsible for the regeneration of tubule epithelium was described by a D₀ value of 1.5 Gy over the dose range 11-16 Gy. This radiosensitivity resembles that of stem cells in acutely responding tissues. The lack of histological evidence of damage to the arterial vasculature at the time the tubules are initially denuded of epithelium, and the similarity of renal tubule cell radiosensitivity to that of other mammalian cells, support the hypothesis that 'late' radiation injury results primarily from depletion of parenchymal cells, not indirectly from injury to blood vessels, as has been the prevailing belief.