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Experimental renal disease was produced in young rats by daily subcutaneous injections of 6-dimethylamino purine, 3-amino-d-ribose (aminonucleoside). The physiologic, biochemical, and light microscopic changes were similar to those observed in human nephrosis. Electron microscopy of the glomeruli from animals which received seven or more daily injections of aminonucleoside revealed characteristic abnormalities of the epithelial cells of the glomerular capillaries. These changes consisted of swelling, coalescence, and eventual obliteration of the epithelial cell foot processes and an increase in the number and the size of epithelial cytoplasmic vacuoles. The serial development of the ultramicroscopic pathologic changes in the epithelial cells, as observed by study of animals through the course of the disease, indicated that the smudging of the foot processes occurred at the time of onset of severe proteinuria. Further changes, consisting of hypercellularity due primarily to an increase in the number of endothelial cells and an increase in the amount of basement membrane-like material, were regularly observed by the 12th day after injections were begun. These abnormalities were correlated with the development of uremia in the later stages of the disease process. The distal and proximal renal tubules were abnormal by the 7th day after injections were begun, and showed localized swelling between the cristae of the mitochondria and a decrease in over-all cytoplasmic density, described as hydropic change. Electron microscopy of glomeruli from animals which had partially recovered from aminonucleoside nephrosis revealed areas of normal epithelial cell morphology. This observation was interpreted as evidence of partial reversal of the ultramicroscopic changes in the recovery phase of the disease. These observations of the fine structure of pathologically altered glomeruli and tubules in aminonucleoside nephrosis are similar to our findings in human nephrosis as revealed by electron microscopy of serial renal biopsies.

Renal biopsies from 16 patients with nephrosis, 7 patients with glomerulonephritis, and 3 patients with disseminated lupus erythematosus were studied with the electron microscope. The observations presented indicate that early in the course of each of these diseases alterations occur in the fine structure of the glomeruli which serve to distinguish one disease process from another. In nephrosis, some distortion of the organization of the epithelial foot processes was seen in all patients. These epithelial changes constituted the early, consistent lesion of the disease. There was frequently also a swelling of the endothelium. In glomerulonephritis, pronounced proliferative changes involving the endothelium and to a lesser extent the epithelium, together with the laying down of a basement membrane-like material, represented the predominate pathologic processes. There was also a swelling of both endothelial and epithelial cytoplasm. The epithelial foot processes generally appeared normal. In patients with a clinically "mixed" picture of nephrosis and nephritis, the glomerular changes were likewise "mixed," for various combinations of epithelial, endothelial, and basement membrane abnormalities were present. In disseminated lupus erythematosus, a more or less generalized thickening of the basement membrane proper associated with a variable degree of endothelial proliferation was seen. It is suggested that an accentuation of the process of basement membrane thickening results in the "wire loop" appearance sometimes seen by light microscopy. Although the earliest alterations in glomerular fine structure were characteristic for each of the disease processes, at later stages the changes were not always distinctive. The resulting scarred or "hyalinized" glomeruli, composed of relatively homogeneous, basement membrane-like material, and a few atrophic cells, appeared quite similar. Although the functional implications of the structural changes observed remain obscure at this time, it is believed that insight into mechanisms may stem from such observations.