Morphology of the renal medulla in ischemic acute renal failure in the rat.

In the initial phase of ischemic acute renal failure in the rat the outer medulla is characterized by widening of peritubular capillaries in the inner stripe and by accumulation of cytoplasmic blebs in dilated proximal straight tubules in the outer stripe. Both findings contribute to tubular obstruction. In the maintenance phase, outer and inner stripes show tubular necrosis mainly of proximal straight tubules and thick ascending loops of Henle. In both phases the papilla is apparently spared from damage. Protective measures act at least partly by prevention of peritubular capillary widening in the inner stripe of outer medulla.