Urology>>>>>Renal Pathophysiology
Question 6#

Regarding post-obstructive diuresis, which of the following is FALSE?

A. Although this occurs mainly after relief of BUO or obstruction of a solitary kidney, it can rarely occur when there is a normal contralateral kidney
B. The normal physiologic diuretic response is due to the volume expansion and solute accumulation occurring during obstruction
C. A pathological postobstructive diuresis, characterised by inappropriate renal handling of water or solutes occurs due to a derangement of the medullary solute gradient and downregulation of sodium transporters with subsequent impaired sodium reabsorption in the distal convoluted tubule
D. There is no role for gradual bladder decompression, because this has not been demonstrated to limit hematuria or reduce the risk of postobstructive diuresis
E. Pathologic postobstructive diuresis is also marked by poor responsiveness of the collecting duct to antidiuretic hormone (ADH)

Correct Answer is C

Comment:

Answer C

POD in UUO with intact contralateral kidney may be because GFR is atypically preserved in the setting of distal tubular damage such that the kidney filters a normal volume but there is limited free water reabsorption. Or this can occur when a pronounced aquaporin channel defect may be present, causing diminished free water absorption in this setting. The diuresis after relief of obstruction is a normal physiologic response to the volume expansion and solute accumulation occurring during obstruction, wherein sodium, urea, and free water are eliminated and the diuresis subsides after solute and fluid homeostasis is achieved. Pathological postobstructive diuresis occurs due to derangement of the medullary solute gradient and downregulation of sodium transporters with subsequent impaired sodium reabsorption in the thick ascending limb of the Henle loop resulting in inappropriate renal handling of water or solutes. Moreover, this can also occur because of poor responsiveness of the collecting duct to antidiuretic hormone (ADH) probably due to a downregulation of aquaporin water channels in this segment of the nephron and perhaps in the proximal tubule.