Quantitative analysis of the developing rat kidney: Absolute and relative volumes and growth curves

The development of the permanent kidney, or metanephros, is a complex proce ss. In the present study, stereological methods were used at the light micr oscopic level to estimate the absolute volumes and volume densities of seve n compartments in the developing rat metanephros, from embryonic day 14 (E1 4) to E21. Metanephroi from time-mated Sprague-Dawley rats were embedded wh ole in glycolmethacrylate, exhaustively sectioned at 2 mu m and stained wit h PAS. The left metanephros from three embryos from each of three mothers w ere analysed at each of the ages (a total of 72 metanephroi). Relative volu mes were multiplied by total metanephric volume to obtain absolute volumes. Total metanephric volume increased approximately 300-fold during the 7-day period studied. At E14, 92% of the metanephros was composed of undifferent iated mesenchyme, whilst the ureteric epithelium made up approximately 5% o f the volume, By E21 the undifferentiated mesenchyme comprised 47% of the k idney, while the ureteric epithelium comprised 9% and the various component s of developing nephrons (epithelial vesicles, comma-shaped bodies, S-shape d bodies, glomeruli, tubules) comprised 43%. Equations with prediction inte rvals describing the growth of the whole kidney as well. as the absolute an d relative growth of the seven kidney compartments were generated, These da ta provide a baseline; for future studies on the roles of specific molecule s in renal development. Anat Rec 258:128-135, 2000. (C) 2000 Wiley-Liss, In c.