Renal 'salt wasting' despite apparently normal renal, adrenal and central nervous system function.

The inability of the kidney to conserve sodium appropriately in response to a restricted sodium intake is reported in a subject who had entirely normal renal and adrenal function and no evidence of central nervous system disease. Subsequent transplantation of his left kidney to his son afforded a unique opportunity to assess renal sodium conservation in each kidney separately: both the patient and his son were unable to achieve balance in response to dietary sodium restriction after transplantation, indicating that the sodium wasting was due to a process intrinsic to both kidneys. The assessment of intrarenal hemodynamics with xenon-133 washout prior to nephrectomy provided insight into the role of intrarenal hemodynamics in the maintenance of sodium homeostasis in man. The xenon washout curve failed to disclose an identifiable second most rapid exponential (CII). This finding, in concert with previous studies demonstrating that diuretic agents with a primary action in the ascending limb of the loop of Henle caused a marked slowing of CII flow, raises the possibility that limited perfusion in the outer medulla of the kidney may be rate-limiting for sodium conservation in man.