Regenerative Versus Nonregenerative Repair of the Renal Medulla After Reversal of Ureteral Obstruction.

Many patients with urinary obstruction have an accelerated decline in renal function despite early urologic interventions. They also have defects in urinary concentrating capacity that may predispose them to acute kidney injury and chronic kidney disease. Because urinary concentrating capacity depends on having intact solute concentrating mechanisms in the renal medulla, it is likely that this results from obstruction-induced abnormalities in renal medullary structure, function, or both. This review focuses on findings from a recent study characterizing the long-term effects of reversible unilateral ureteral obstruction in mice that address these questions. These findings show that there is delayed long-term growth of the inner medulla, which is initially shrunken, that results in complete restoration of inner medullary size and gross tissue architecture 3 months after reversal of the obstruction. More detailed analysis shows that despite relatively normal histologic appearances, there are permanent defects in the cellular organization and function of the medulla that account for the loss of urinary concentrating capacity. We discuss the extent to which regenerative versus nonregenerative repair mechanisms may contribute to the growth and functional recovery of the renal medulla and consider how these findings shed light on the mechanisms of tissue repair and dysfunction after reversal of urinary obstruction.