Establishment of a Strain of a Rat Having Extremely High Incidence of Congenital Hydronephrosis and Its Morphological Characteristics

Abstract

A strain of rats having extremely high incidence of congenital hydronephrosis, originating from the Wistar-Imamichi rat, was established through sister-brother mating for 11 filial generations following selection breeding for 5 generations. The hydronephrosis appeared in all litters and approximately 70% of the total littermates at the 16th generation (the 12th sister-brother mating). Anatomical characteristics, incidence and distribution of the hydronephrosis were observed during the breeding. Fetal kidneys on day 20 of gestation obtained from the hydronephrosis rat (HNR) were compared to "apparent hydronephrosis" described by Woo and Hoar (1972). Hydronephrosis in the HNR strain could be classified into two types ; cystic kidney type (type I ) and pelvic dilatation type (type II ). Neither obstruction in the urinary pathway nor defects of ureter and genital system was found in both types of the hydronephrosis. Since bilateral hydronephrosis began to appear at the 8th generation (the 4th sister-brother mating) and the incidence became higher with the filial generations, this anomaly was probably a polygenic trait which affects differentiation of metanephros. Cystic kidney was observed in the fetus on day 20 of gestation with a high incidence, and its morphological feature was different from that of "apparent hydronephrosis".A strain of rats having extremely high incidence of congenital hydronephrosis, originating from the Wistar-Imamichi rat, was established through sister-brother mating for 11 filial generations following selection breeding for 5 generations. The hydronephrosis appeared in all litters and approximately 70% of the total littermates at the 16th generation (the 12th sister-brother mating). Anatomical characteristics, incidence and distribution of the hydronephrosis were observed during the breeding. Fetal kidneys on day 20 of gestation obtained from the hydronephrosis rat (HNR) were compared to "apparent hydronephrosis" described by Woo and Hoar (1972). Hydronephrosis in the HNR strain could be classified into two types ; cystic kidney type (type I ) and pelvic dilatation type (type II ). Neither obstruction in the urinary pathway nor defects of ureter and genital system was found in both types of the hydronephrosis. Since bilateral hydronephrosis began to appear at the 8th generation (the 4th sister-brother mating) and the incidence became higher with the filial generations, this anomaly was probably a polygenic trait which affects differentiation of metanephros. Cystic kidney was observed in the fetus on day 20 of gestation with a high incidence, and its morphological feature was different from that of "apparent hydronephrosis".