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1 The Water and Salt Research Center, University of Aarhus, Aarhus C, Denmark; Institute of Anatomy, University of Aarhus, Aarhus C, Denmark
2 The Water and Salt Research Center, University of Aarhus, Aarhus C, Denmark; Department of Biochemistry and Cell Biology, School of Medicine, Kyungpook National University, Taegu, Korea, Republic of
3 The Water and Salt Research Center, University of Aarhus, Aarhus C, Denmark; Institute of Clinical Medicine, University of Aarhus, Aarhus C, Denmark
4 Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA
* To whom correspondence should be addressed. E-mail: sn{at}ana.au.dk.
Vasopressin and aldosterone are essential hormones in the regulation of water and sodium balance. Aldosterone is thought to mainly affect sodium reabsorption although synergistic effects on the vasopressin-mediated increase in collecting duct water permeability have been shown. Moreover, it has been shown that aldosterone may affect water balance in the absence of vasopressin. In this study we investigate the role of aldosterone in the regulation of water balance and the AQP2 expression in rats with lithium-induced nephrogenic diabetes insipidus (Li-NDI) and in Brattleboro (BB) rats with congenital central diabetes insipidus (CDI). The effect of 7-day aldosterone (200 µg/day s.c. infusion) or spironolactone (200 mg/kg/day p.o.) treatment was investigated in rats with Li-NDI (0.8mmol Li+/day for 21 days). In rats with Li-NDI, aldosterone markedly increased (271±14 ml/24h) while spironolactone decreased (74±11 ml/24h) urine production compared to control Li-DI rats (120±11 ml/24h). The aldosterone-induced diuresis was associated with increased free-water clearance and creatinine clearance whereas spironolactone caused a decreased creatinine clearance but unchanged free-water clearance. In the aldosterone-treated and spironolactone-treated rats with Li-NDI, immunoblotting of AQP2 showed no changes in cortex/OSOM and inner medulla (IM) compared to control Li-NDI rats. In contrast the AQP2 expression in ISOM was decreased in response to aldosterone treatment (81±5%) and increased in response to spironolactone treatment (132±5%) compared to control Li-NDI rats. In parallel to the changes in urine production, immunohistochemical analysis and semiquantitative confocal immunofluorescence microscopy showed a marked reduction in the apical plasma membrane domain AQP2 expression in connecting tubule (CNT) and initial cortical collecting ducts (iCCD) in response to aldosterone treatment compared with control Li-NDI rats. Conversely, spironolactone significantly increased apical AQP2 expression in the iCCD compared to Li-NDI rats. To test whether these changes in response to aldosterone and spironolactone also could be seen in rats with CDI, parallel experiments were made in vasopressin-deficient BB rats, revealing similar observations. Aldosterone increased (323±9 ml/24h) and spironolactone decreased (127±3 ml/24h) urine production compared to untreated BB rats (182±7 ml/24h). Moreover decreased and increased AQP2 apical expression was seen in response to aldosterone or spironolactone treatment, respectively. The study shows that aldosterone treatment perturbs DI and this was associated with an aldosterone-mediated AQP2 redistribution in CNT and iCCD mediated by the spironolactone-sensitive mineralocorticoid receptor.
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