Abstract
The kidneys of 43 male Sprague-Dawley rats, mostly 12-18 months old, were examined by electron microscopy. Paraffin sections stained with the allochrome procedure and thick epoxy sections stained with toluidine blue were used to select sites of nephrotic changes. Protein levels in urine were monitored periodically. The basement membranes of affected nephrons showed a two- to threefold thickening in the capillary loops and Bowman's capsule. Epithelial cells in the glomeruli underwent compensatory changes of hypertrophy, fusion of foot processes and occasionally microvillar transformation. Dense granular material as well as protein absorption droplets formed in the epithelial cells. Epithelial cells of proximal convolutions atrophied and disappeared as the basement membrane thickened to several micrometers. An increase of dense bodies, granular material, and focal cytoplasmic degradation was observed in these cells. The ongoing irreversible deterioration of scattered nephrons suggested the designation of chronic progressive nephrosis for this common disease of Sprague-Dawley rats over 1 year old.