title: Angiotensin II AT1 receptor blockade decreases vasopressin-induced water reabsorption and AQP2 levels in NaCl-restricted rats.
abstract: Vasopressin and ANG II, which are known to play a major role in renal water and sodium reabsorption, are mainly coupled to the cAMP/PKA and phosphoinositide pathways, respectively. There is evidence for cross talk between these intracellular signaling pathways. We therefore hypothesized that vasopressin-induced water reabsorption could be attenuated by ANG II AT(1) receptor blockade in rats. To address this, three protocols were used: 1) DDAVP treatment (20 ng/h sc for 7 days, n = 8); 2) DDAVP (20 ng/h sc for 7 days) and candesartan (1 mg.kg(-1).day(-1) sc for 7 days) cotreatment (n = 8); and 3) vehicle infusion as the control (n = 8). All rats were maintained on a NaCl-deficient diet (0.1 meq Na(+).200 g body wt(-1).day(-1)) during the experiment. DDAVP treatment alone resulted in a significant decrease in urine output (3.1 +/- 0.2 ml/day) compared with controls (11.5 +/- 2.2 ml/day, P < 0.05), whereas the urine output was significantly increased in response to DDAVP and candesartan cotreatment (9.8 +/- 1.0 ml/day, P < 0.05). Consistent with this, rats cotreated with DDAVP and candesartan demonstrated decreased urine osmolality (1,319 +/- 172 mosmol/kgH(2)O) compared with rats treated with DDAVP alone (3,476 +/- 182 mosmol/kgH(2)O, P < 0.05). Semiquantitative immunoblotting revealed significantly decreased expression of medullary aquaporin-2 (AQP2) and AQP2 phosphorylated in the PKA phosphorylation consensus site Ser-256 (p-AQP2) in response to DDAVP and candesartan cotreatment compared with DDAVP treatment alone. In addition, cortical and medullary AQP1 was also downregulated. Fractional sodium excretion (FE(Na)) and plasma potassium levels were markedly increased, and the expressions of the cortical type 3 Na(+)/H(+) exchanger (NHE3), thiazide-sensitive Na-Cl cotransporter (NCC), and Na-K-ATPase were significantly decreased in response to DDAVP and candesartan cotreatment. Moreover, medullary type 1 bumetanide-sensitive Na-K-2Cl cotransporter expression showed a marked gel mobility shift from 160 to approximately 180 kDa corresponding to enhanced glycosylation, whereas expression was unchanged. In conclusion, ANG II AT(1) receptor blockade in DDAVP-treated rats was associated with decreased urine concentration and decreased AQP2 and AQP1 expression. Moreover, FE(Na) was increased in parallel with decreased expression of NHE3, NCC, and Na-K-ATPase. These results suggest that ANG II AT(1) receptor activation plays a significant role in regulating aquaporin and sodium transporter expression and modulating urine concentration in vivo.
authors.affiliation: The Water and Salt Research Ctr, Bldg. 233/234, Univ. of Aarhus, DK-8000 Aarhus C, Denmark.
authors.forename: Tae-Hwan
authors.initials: TH
authors.lastname: Kwon
authors.forename: Jakob
authors.initials: J
authors.lastname: Nielsen
authors.forename: Mark A
authors.initials: MA
authors.lastname: Knepper
authors.forename: Jørgen
authors.initials: J
authors.lastname: Frøkiaer
authors.forename: Søren
authors.initials: S
authors.lastname: Nielsen
mesh_terms: D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology*; D000818:Animals; D051398:Aquaporin 1; D051399:Aquaporin 2; D020346:Aquaporins / Q000378:metabolism*; D001562:Benzimidazoles / Q000494:pharmacology*; D001713:Biphenyl Compounds; D001806:Blood Urea Nitrogen; D003404:Creatinine / Q000378:metabolism; D003894:Deamino Arginine Vasopressin / Q000494:pharmacology*; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism; D008297:Male; D009994:Osmolar Concentration; D010766:Phosphorylation; D011188:Potassium / Q000652:urine; D051381:Rats; D017208:Rats, Wistar; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D011955:Receptors, Drug / Q000378:metabolism; D012076:Renal Agents / Q000494:pharmacology*; D012964:Sodium / Q000652:urine; D049992:Sodium Chloride Symporters; D017673:Sodium Chloride, Dietary / Q000494:pharmacology; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D064466:Solute Carrier Family 12, Member 1; D064486:Solute Carrier Family 12, Member 3; D027981:Symporters / Q000378:metabolism; D013777:Tetrazoles / Q000494:pharmacology*; D014867:Water / Q000378:metabolism
chemical_list: D047228:Angiotensin II Type 1 Receptor Blockers; C496022:Aqp1 protein, rat; C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D020346:Aquaporins; D001562:Benzimidazoles; D001713:Biphenyl Compounds; D044140:Receptor, Angiotensin, Type 1; D011955:Receptors, Drug; D012076:Renal Agents; C578716:Slc12a1 protein, rat; C578876:Slc12a3 protein, rat; C000613387:Slc9a3 protein, rat; D049992:Sodium Chloride Symporters; D017673:Sodium Chloride, Dietary; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D064486:Solute Carrier Family 12, Member 3; D027981:Symporters; D013777:Tetrazoles; C064415:thiazide receptor; D014867:Water; D051398:Aquaporin 1; D012964:Sodium; D003404:Creatinine; D000254:Sodium-Potassium-Exchanging ATPase; D003894:Deamino Arginine Vasopressin; D011188:Potassium; C081643:candesartan