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Background and objectives The predictors of long–term renal function in living kidney donors are currently discussed. Our objectives were to describe the predictors of functional gain of the remaining kidney after kidney donation. We hypothesized that GFR of the remaining kidney divided by volume of this kidney (rk-GFR/vol) would reflect the density of functional nephrons and be inversely associated with functional gain of the remaining kidney. Design, setting, participants, & measurements We conducted a prospective monocentric study including 63 living donors (26 men; 50.3±11.8 years old) who had been evaluated for 51Cr-EDTA and measured GFR, split renal function by scintigraphy before donation (between 2004 and 2009), and measured GFR at 5.7±0.5 years after donation. For 52 donors, volume of the remaining kidney (measured and estimated with the ellipsoid formula using renal computed tomography scannography) was determined before donation. We tested our hypothesis in an external validation cohort of 39 living donors (13 men; 51.0±9.4 years old) from another single center during the same time period. Results For the main cohort, the mean measured GFR was 97.6±13.0 ml/min per 1.73 m2 before donation and 63.8±9.4 ml/min per 1.73 m2 at 5 years. Functional gain averaged 16.2±7.2 ml/min per 1.73 m2 (+35.3%±16.7%). Multivariate analysis showed that age, body mass index, and rk-GFR/vol at donation were negatively correlated with functional gain and had strong predictive power of the 5-year functional gain (adjusted 5-year functional gain for age: −0.4 [95% confidence interval (95% CI), −0.5 to −0.1]; body mass index: −0.3 [95% CI, −0.6 to −0.1]; rk-GFR/vol: −55.1 [95% CI, −92.3 to −17.9]). We tested this model in the external validation cohort (adjusted 5-year functional gain for age: −0.1 [95% CI, −0.5 to 0.3]; body mass index: −0.9 [95% CI, −1.8 to −0.1]; rk-GFR/vol: −97.6 [95% CI, −137.5 to −57.6]) and confirmed that rk-GFR/vol was inversely associated with 5-year functional gain. Conclusions For given age and body mass index, the long–term functional gain of the remaining kidney is inversely associated with the new variable rk-GFR/vol at donation.

Purpose of review: There is consensus that the abnormal retention of sodium by the kidney is the most important pathophysiological event in hypertension. The present review summarizes our current understanding of sodium reabsorption in the distal nephron. Recent findings: The antihypertensive effect of thiazides is thought to be mediated by inhibiting Na+ uptake via the NaCl cotransporter NCC in the distal convoluted tubule. Although it was known that thiazide-sensitive Na⁺ reabsorption in isolated cortical collecting ducts can occur independently of the epithelial Na⁺ channel ENaC, its molecular correlate was unresolved. It was absent in isolated cortical collecting ducts of mice with a targeted disruption of the Na⁺-driven chloride/bicarbonate exchanger NDCBE suggesting that this pathway involves apical Na⁺ uptake into intercalated cells via the Na⁺-driven anion-exchanger NDCBE (SLC4A8). Summary: The finding that SLC4A8-dependent thiazide-sensitive Na⁺ reabsorption occurs in the cortical collecting duct challenges our current model of how thiazides mediate their antihypertensive action and identifies a potentially new target for antihypertensive strategies.

Recent studies indicate that pendrin, an apical Cl-/HCO3- exchanger, mediates chloride reabsorption in the connecting tubule and the cortical collecting duct and therefore is involved in extracellular fluid volume regulation. The purpose of this study was to test whether pendrin is regulated in vivo primarily by factors that are associated with changes in renal chloride transport, by aldosterone, or by the combination of both determinants. For achievement of this goal, pendrin protein abundance was studied by semiquantitative immunoblotting in different mouse models with altered aldosterone secretion or tubular chloride transport, including NaCl loading, hydrochlorothiazide administration, NaCl co-transporter knockout mice, and mice with Liddle's mutation. The parallel regulation of the aldosterone-regulated epithelial sodium channel (ENaC) was examined as a control for biologic effects of aldosterone. Major changes in pendrin protein expression were found in experimental models that are associated with altered renal chloride transport, whereas no significant changes were detected in pendrin protein abundance in models with altered aldosterone secretion. Moreover, in response to hydrochlorothiazide administration, pendrin was downregulated despite a marked secondary hyperaldosteronism. In contrast, alpha-ENaC was markedly upregulated, and the molecular weight of a large fraction of gamma-ENaC subunits was shifted from 85 to 70 kD, consistent with previous results from rat models with elevated plasma aldosterone levels. These results suggest that factors that are associated with changes in distal chloride delivery govern pendrin expression in the connecting tubule and cortical collecting duct.