Spontaneous renal lesions in five rat strains.

A survey of non-neoplastic and neoplastic renal lesions found in 5 rat strains, namely, ACI (August X Copenhagen Irish), A22807 (August), F344 (Fischer), M520 (Marshall), and OM (Osborne-Mendel) is given. The results from this survey indicate that the OM, M520, and ACI rat strains have major disadvantages for their use in long-term toxicology and carcinogenesis studies. Male OM rats had a high incidence of renovascular lesions which consisted of necrotizing arteritis or arteriolitis and intimal thickening of small arteries, and resembled renal lesions described in hypertensive rats and human patients. Predominant renal lesions in the M520 and ACI rat strains included extensive calculus formation at the pyramido-pelvic junction, which was often associated with proliferative pelvic transitional cell lesions and hydronephrosis. The ACI rat strain also had unilateral congenital renal agenesis in about 12% of the animals of either sex. Based on the spectrum of renal lesions observed in the 2 remaining rat strains, namely A28807 and F344, it is difficult to determine which one of the two should be preferred for long-term studies. The A28807 rat strain had less severe chronic renal disease than the F344 but had a higher incidence of pelvic transitional cell hyperplasia. The ultimate choice should be based on the spectrum, incidence, and severity of extra-renal lesions.