Renal hemodynamics and medullary osmolal gradient in ischemic acute renal failure in rabbits

The effects of 2 hours of renal artery occlusion were studied in previously uninephrectomized rabbits. Oliguric renal failure by arterial clamping was produced. Renal blood flow was maintained during observation periods, except for an early decrease in outer cortical blood flow without change elsewhere. During the oliguric stage medullary osmolality was markedly diminished, concomitantly with reduced (U/P)osm. Cin, EPAH and sodium reabsorption were decreased, accompanied by tubular necrosis and intratubular casts. During the early diuretic stage Cin, medullary osmolality and (U/P)osm were still reduced. Intratubular casts disappeared while regenerated tubular cells were focally observed. Two weeks after the occlusion, improved Cin, EPAH, sodium reabsorption, medullary osmolality and (U/P)osm, and regenerated tubular epithelium were found. In 7 weeks Cin and EPAH had returned to the preclamping values whereas medullary osmolality remained decreased with the appearance of medullary fibrosis. (U/P)osm was not completely restored. The findings indicate that during the oliguric stage of acute renal failure of rabbits renal blood flow is maintained, except for a decrease in outer cortical flow, and urine concentrating ability is restored more slowly than other measured functions.