Disproportionate inhibition of sodium reabsorption in the unilaterally diseased kidney of dog and man after an acute saline load

Clearance studies were performed on 49 split-bladder dogs with a unilateral pyelonephritic or remnant kidney and three patients with unilateral kidney disease to examine the effects of an acute saline load on the diseased kidney (DK) as opposed to a simultaneously studied, contralateral control kidney (CK), which also served to maintain a nonuremic environment. Before saline loading, base line studies in many of the dogs and the three humans were in agreement with previously published data. However, in dogs with a severe pyelonephritic lesion, a greater difference in DK vs. CK fractional excretion of sodium (FE(Na)) and water was noted, whose magnitude was inversely correlated with the level of glomerular filtration rate (GFR) and maximum urine osmolality of DK compared to CK. An acute saline load (75 ml/kg) resulted in an inhibition of fractional sodium and water reabsorption in the diseased dog kidney which was disproportionately greater than in the simultaneously studied CK, regardless of the type or severity of the lesion. While mean DK GFR for all dogs increased 15% more than CK GFR, failure of FE(Na) to increase after induction of a disproportionate increase in DK GFR with parathyroid hormone suggested that the saline-induced disproportionate increase in GFR was not solely responsible for the exaggerated inhibition of fractional sodium and water reabsorption in the diseased dog kidney. Studies in the three patients after saline loading (25 ml/kg) revealed a similar disproportionate resetting of glomerulotubular balance.Thus, regardless of base line function before expansion, the unilaterally diseased kidney of dog and man possesses unique characteristics in the absence of uremia which render it more reactive to the stimuli produced by acute saline loading. This suggests that the intrarenal environment of the kidney with a reduced nephron population may under some circumstances serve as a determinant of its function.