Sequential functional testing of radiation-induced renal damage in the mouse.

Two nondestructive assays of functional impairment were developed to measure renal damage in mice after local irradiation of both kidneys with 240-kV X rays. Daily urine output after irradiation was measured indirectly by determining urination frequency. A dose-related response began 17 weeks after treatment and then progressed; dose-response curves with a threshold of 12 Gy were established by 22 weeks. The time of onset of damage was dose related and there was some recovery of kidney function between 25 and 38 weeks. The rate of excretion of 51Cr-EDTA was measured as an estimate of glomerular filtration either by sequential external counting over 20 min or from the activity remaining in a single blood sample at 60 min. Both methods gave dose-response curves, but the results from the blood sample were more precise. These assays are suitable for sequential testing of individual mice and have been used to establish a dose-related latent period of approximately 17 weeks after bilateral renal irradiation.