Stereological study of the kidney during prenatal development in sheep.

The development of metanephros is a complex and gradual process. The number, size and distribution of nephrons provide important information about the organization of the kidney. Stereology is the current gold-standard technique for the morphometrical evaluation of kidney structures. This study describes morphometric features of the kidney development in sheep using design-based stereological techniques aimed to introduce the sheep as a translational model in human nephrogenesis. Left kidneys of 16 sheep fetuses in four groups at 9-11, 12-14, 15-17, and 18-20 weeks of gestation were used in the present study. Systematic uniform random sections were obtained. The kidney volume, volume fraction of nephrogenic zone, cortex and medulla, and glomerular volume were estimated using point counting and Cavalieri's estimator. The total glomerular number was estimated using a physical disector/fractionator technique. The kidney and its compartments presented gradual changes with aging, with differences found in the last fetal ages. The kidney volume increased from 0.94 ± 0.22 cm3 to 8.6 ± 0.88 cm3 during development. The volume of cortex increased from 406 ± 85 mm3 to 5,151 ± 309 mm3 and the volume of medulla showed increase from 301 ± 91 mm3 to 3,426 ± 599 mm3 . The total glomerular volume increased from 13.8 ± 1.6 mm3 to 235 ± 44 mm3 . The total glomerular number increased from 4,683 ± 757 to 639 × 103  ± 11.6 × 103 . Our data might contribute to the knowledge of embryological urology and promote future experimental investigations in this field.