The vulnerability of the thin descending limbs of Henle's loop in the isolated perfused rat kidney.

In the isolated rat kidney perfused without erythrocytes, the medullary thick ascending limb shows extensive injury. Damage to the thin limbs of Henle's loop has been mentioned only briefly. Thin limbs were examined in the isolated perfused kidney under a variety of conditions that alter oxygenation and active transport in the medulla and are known to affect injury to the medullary thick ascending limb. The thin descending limbs of short loops were preserved in all experimental groups, but those of the long loop showed necrosis that was restricted to the proximal portion, where the epithelium is more complex. In oxygenated kidneys, necrosis involved 41% +/- 5% (mean +/- SE) of the medullary thick ascending limbs and 10% +/- 3% of the proximal portion of long loops of thin descending limbs. Under hypoxic conditions, necrosis involved 90% +/- 3% of the medullary thick ascending limbs and 70% +/- 5% of the proximal portion of long loops of thin descending limbs (P less than 0.0001 compared with oxygenated kidneys). Ouabain and absence of filtration completely prevented necrosis of both nephron segments. Thus, the proximal portions of long loops of thin descending limbs, in resemblance to medullary thick ascending limbs, are especially susceptible to transport-dependent hypoxic injury.