HEREDITARY HYDRONEPHROSIS IN C57BL/KSJ MICE

We sought to determine if the incidence of renal hydronephrosis in male C57BL/KsJ mice increased with age and if grossly normal kidneys would develop hydronephrosis over time. Spontaneous hydronephrosis was found incidentally in 32% of 234 male C57BL/KsJ mice killed as pancreas donors for islet transplantation experiments. The incidence of hydronephrosis increased with age; the incidence was 15% in 6- to 8-week-old mice, 52% in 8- to 10-week-old mice and 63% in 11- to 15-week-old mice (P < 0.001). Additional mice received islet isografts beneath the renal capsule. Only mice with grossly normal kidneys received islet grafts. These same kidneys were then re-examined when the graft recipients were killed at the end of the experiment and the incidence of hydronephrosis was determined. The conversion of normal kidneys to hydronephrotic kidneys increased with the time since islet transplantation. Kidneys re-examined less than 4 weeks since transplantation had only 5.8% new hydronephrosis, while those re-examined later than 4 weeks after transplantation had a new hydronephrosis incidence rate of 40% (P < 0.001). Our findings suggest that hydronephrosis is hereditary but not congenital, that it develops rapidly, and that it can complicate experiments using this strain. This may also represent a useful new animal model of progressive hydronephrosis.