Radiation injury in the neonatal canine kidney. I. Pathogenesis.

The effects of radiation on the developing canine kidney were investigated. Beagles were exposed to 330 R 60Co gamma-radiation on the 2nd postnatal day of life. The kidneys were examined at 2 days (6 hours after irradiation), 4, 8, 14, 22, 70, and 200 days of age with qualitative and quantitative light microscopy and scanning electron microscopy. The primary result of the radiation injury was a failure to form the normal number of nephrons. The kidneys of irradiated dogs had 42 per cent fewer nephrons (260,000) than the control dogs (445,000). In addition, extensive damage to forming nephrons produced dysplastic renal corpuscles and other corpuscles which were arrested in their development. Three mechanisms of radiation injury were identified. First, there was extensive mitosis-linked cell death in the nephrogenic zone. Second, mitotic delay resulted in only one-fifth of the normal mitotic activity in the nephrogenic zone through 2 days postirradiation. Third, there was an immediate and permanent cessation of nephron formation. The extensive injury in the outer renal cortex was compounded by the development of intercapillary glomerulosclerosis in some middle and inner cortical corpuscles by 200 days of age.