Pathophysiology and postnatal pathogenesis of hypoplastic kidney (hpk/hpk) in the male hypogonadic mutant rat (hgn/hgn).

The male hypogonadic rate (hgn/hgn) is accompanied with bilateral hypoplastic kidney (HPK; hpk/hpk)[34]. In this study, we examined the kidney weight (KW), glomerular number (GN), renal pathohistology at adult (80 days of age), and pathogenesis during the early postnatal stage in the hpk/hpk, +/hpk, and +/+ rat. The GN of adult hpk/hpk was significantly less that that of the +/hpk and +/+. Histologically, there were the decreased number of nephrons and the associated secondary changes in the hpk/hpk kidney. The plasma concentrations of urea nitrogen and creatinine were significantly higher in the hpk/hpk than in the +/hpk and +/+. During early postnatal stage, the KW of the hpk/hpk was significantly smaller than those of the +/hpk and +/+, and the GN was fewer in order of the hpk/hpk, +/hpk and +/+, showing the significant differences between given genotypes. The layer of nephrogenic nephron beneath the renal capsula of the neonatal kidney appeared to be thinner in the hpk/hpk than in the normal (+/hpk and +/+). In the hpk/hpk kidney on 3 days of age, the layer of the nephrogenic nephron was absent in some portions beneath the renal capsula. In the hpk/hpk kidney on 7 days of age, further, the layer of immature type of nephron was still observed under the capsula. These studies suggest that the hypoplastic kidney, which may result from reduced nephrogenesis, could not compensate the real weight, GN and renal function during the postnatal nephrogenic stage.