Ultrastructure of medullary tubules in ischemic acute tubular necrosis and acute interstitial nephritis in man.

Medullary tubules in renal biopsies from twelve patients suffering from ischemic acute tubular necrosis (ATN) and nine patients with allergic, drug-induced acute interstitial nephritis (AIN) were investigated by electron microscopy using quantitative and semiquantitative methods. For comparison, 12 biopsies from patients without renal disease or with minimal change nephropathy were studied. The mean scores for reduction of brush border and basolateral infoldings of the cell surface were significantly increased in the straight part of the proximal tubule and the thick ascending loop of Henle (straight part of the distal tubule) compared with medullary controls, and these changes were significantly greater than the scores for the corresponding convoluted tubules in the cortex. The numbers of missing tubular epithelial cells (indicating sites of cellular desquamation) were significantly increased in the thick ascending loop of Henle in ATN as well as in AIN and in the straight proximal tubule in ATN. This single cell lesion also occurred in the collecting duct. These findings are discussed in the light of recent experimental data indicating the importance of medullary tubules for the pathogenesis of ATN.