1 Department of Pharmacology, the Panum Institute, University of Copenhagen, 2200 Copenhagen N; and the 2 Department of Cell Biology, Institute of Anatomy, University of Arhus, Arhus DK-8000, Denmark
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The present study was performed to investigate the renal
handling of water in rats with decompensated liver cirrhosis. Liver cirrhosis was induced by intraperitoneal administration of carbon tetrachloride twice weekly for 16 wk. Control rats were treated with
vehicle. The cirrhotic rats developed severe disturbances in water
homeostasis: urine production was decreased and hyperosmotic, the rats
had significantly decreased plasma sodium concentration and ascites,
and the ability to excrete an intravenous water load was significantly
impaired. Plasma concentrations of vasopressin and aldosterone were
increased. Mean arterial pressure, glomerular filtration rate (GFR),
and fractional lithium excretion were decreased. Acute vasopressin type
2-receptor blockade with the selective nonpeptide antagonist OPC-31260
(800 µg · kg1 · h
1) was
performed during conditions whereby volume depletion was prevented by
computer-driven, servo-controlled intravenous volume replacement with
150 mM glucose. The aquaretic response to OPC-31260 was similar in
cirrhotic and control rats. However, the OPC 31260-induced rises in
fractional water excretion (
V/GFR; +24%) and fractional distal
water excretion (
V/CLi; +46%) were significantly
increased in the cirrhotic rats, where V is flow rate and
is
change. This suggests that vasopressin-mediated renal water
reabsorption capacity was increased in the cirrhotic rats.
Semiquantitative immunoblotting revealed that the expression of the
vasopressin-regulated water channel aquaporin-2 was unchanged in
membrane fractions of both whole kidney and inner medulla from
cirrhotic rats. Together, these results suggest a relative escape from
vasopressin on collecting duct water reabsorption in rats with
decompensated liver cirrhosis.
aquaporin-2; OPC-31260; collecting ducts; carbon tetrachloride; vasopressin type 2 receptor
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
A NUMBER OF PATHOPHYSIOLOGICAL conditions are associated with increased plasma levels of vasopressin and extracellular fluid expansion. Experimental studies in rats with congestive heart failure, induced by left coronary artery ligation (31, 40), showed that severe decompensated congestive heart failure with hyponatremia was associated with an increased abundance of the vasopressin-regulated water channel aquaporin-2 (AQP2). However, rats with nephrotic syndrome induced by puromycin aminonucleoside, had a significantly decreased AQP2 abundance despite high levels of plasma vasopressin (1). Studies from rats with liver cirrhosis have shown conflicting results with regard to the renal expression of AQP2. Initial studies showed increased expression of AQP2 mRNA and protein in CCl4-induced cirrhotic rats with ascites (2, 13). However, we have recently found decreased abundance of AQP2 protein in rats with liver cirrhosis induced by common bile duct ligation (16, 18). The rats had sodium retention, slightly increased plasma levels of vasopressin, normal plasma sodium concentrations, normal 24-h urine production, and no sign of ascites. Renal clearance experiments showed that the decreased AQP2 abundance was associated with a significantly decreased aquaretic response to acute, selective vasopressin type 2 (V2)-receptor blockade, which suggests that vasopressin-mediated renal water reabsorption is decreased in the common bile duct ligation model of liver cirrhosis. Recently, Fernandez-Llama et al. (11) confirmed that AQP2 abundance is significantly decreased in rats with liver induced by common bile duct ligation. Compared with our model, these rats had ascites and hyponatremia, which indicate that water retention with the formation of hyponatremia can occur in the absence of increases in AQP2 abundance.
One question to be answered is whether the reported differences in AQP2 expression in experimental cirrhosis are due to the model used or the fact that the rats were investigated at different stages of the disease, i.e., that AQP2 expression may be downregulated in the preascitic state and during early decompensation and then increased in terminal conditions with severe decompensation.
The present study was made in rats with decompensated liver cirrhosis induced by CCl4. Vehicle-treated rats were used as controls. The cirrhotic rats had significantly decreased plasma sodium concentration (hyponatremia), ascites, and increased plasma levels of vasopressin and showed an impaired ability to excrete an intravenous (iv) water challenge. V2 receptor-mediated water reabsorption in the collecting duct was examined as the aquaretic response to acute, selective V2-receptor blockade in chronically instrumented rats. V2-receptor blockade was achieved in the absence of changes in fluid balance by use of a computer-driven, servo-controlled iv volume replacement system. The renal abundance of the AQP2 protein was determined by semiquantitative immunoblotting in additional groups of rats.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Materials
Barrier-bred and specific pathogen-free female Wistar rats (210-230 g) were obtained from the Department of Experimental Medicine, Panum Institute, University of Copenhagen, Denmark. The animals were housed in a temperature (22-24°C)- and moisture (40-70%)-controlled room with a 12:12-h light-dark cycle (lights on from 6:00 AM to 6:00 PM). All animals were given free access to tap water and a pelleted rat diet containing ~140 mmol/kg sodium, 275 mmol/kg potassium, and 23% protein (Altromin catalogue no. 1310, Altromin, Lage, Germany).Animal Preparation
Liver cirrhosis was induced by intraperitoneal (ip) injections of a solution of CCl4 in groundnut oil (1:1), 1 ml/kg body wt twice a week throughout the experimental period. Control rats received ip injections of groundnut oil 0.5 ml/kg body wt. To accelerate the generation of cirrhosis, all rats received phenobarbital in the drinking water (350 mg/ml) throughout.After 14-wk treatment with CCl4 or vehicle, rats that were subjected to renal function studies were anesthetized with halothane-nitrous oxide, and permanent medical-grade Tygon catheters were implanted into the abdominal aorta and into the inferior caval vein via a femoral artery and vein. A permanent suprapubic bladder catheter was implanted into the urinary bladder and sealed with a silicone-coated stainless steel pin after flushing of the bladder with ampicillin (0.6 mg/ml, Anhypen, Nycomed Pharma, Oslo, Norway). Catheters were produced, fixed, and sealed as previously described (14-19, 33). All surgical procedures were performed during aseptic conditions. To relieve postoperative pain, rats were treated with buprenorfin, 0.2 mg/kg body wt ip twice daily for 2 days (Anorfin, GEA, Copenhagen, Denmark). After instrumentation, the animals were housed individually.
Urine Production and Sodium Balance
In the beginning of study week 16, the rats were placed in metabolic cages (Techniplast, model 1700, Scandbur, Lellinge, Denmark). The rats received demineralized water and granulated standard diet (Altromin catalogue no. 1310, Altromin) that contained 133 mmol Na/kg. Sodium intake was calculated from the amount of diet ingested per 24 h, and sodium loss was estimated from the amount of sodium excreted in the urine within the same 24 h. Twenty-four-hour urine production was measured gravimetrically, and then the metabolic cage was rinsed with 40-50 ml of demineralized water to optimize the recovery of sodium. The sodium content was measured in the combined volume of urine and demineralized water, and 24-h sodium balance was then calculated as sodium intake minus urinary sodium losses. After 2 days of adaptation, 24-h sodium balance was measured for 3 consecutive days, and the average of the three values was used.Renal Clearance Experiments
Renal function was examined by clearance techniques at the end of study week 16. Before the renal clearance experiments, all rats were adapted to the restraining cage used for these experiments by training them for two periods of 2 h each. To examine the rats at the same level of hydration, all experiments were started at 9:00 AM. Renal function was examined by clearance techniques whereby 14[C]tetraethylammonium bromide clearance was used as a marker for the effective renal plasma flow (32), 3[H]inulin clearance as a marker for glomerular filtration rate (GFR), and lithium clearance as a marker for the delivery of fluid from the proximal tubule (38). Renal clearances and fractional excretions were calculated by the standard formula
![]() |
After a 90-min equilibration period, urine was collected during two
30-min control periods. Arterial blood samples of 300 µl each were
collected into ammonium-heparinized capillary tubes at the end of the
equilibration period and at the end of the control periods. At the
beginning of the equilibration period (i.e., at 9:00 AM), a 0.2-ml
blood sample was collected for measurement of plasma sodium and
potassium concentrations and plasma osmolality, and, for measurement of
the plasma concentration of vasopressin, a 1.0-ml blood sample was
collected in a prechilled test tube with 20 µl 0.5 M EDTA, pH 7.4, and 10 µl 20 × 106 IE/ml aprotinin. After
centrifugation at 4°C, plasma was transferred to a prechilled test
tube and stored at 20°C for later determination. All blood samples
was replaced immediately with heparinized blood from a normal donor
rat. After the second control period, the rats where subjected to
either protocol 1 or protocol 2.
Protocol 1: Renal function during iv water loading. The ability to excrete an iv water challenge was examined in six vehicle- and six CCl4-treated animals. After the control period, the rats received an iv infusion of 10 ml 50 mM glucose (infusion rate 1 ml/min). Urine collections were made in a 15-min period during the next 3 h. Arterial blood samples of 300 µl each were collected 1, 2, and 3 h after the start of the water loading.
Protocol 2: Renal function before and during acute V2
receptor blockade.
The aquaretic response to acute V2-receptor blockade was
examined in eight vehicle- and eight CCl4-treated animals.
Infusion (iv) of the selective V2-receptor antagonist
OPC-31260 (prime: 400 µg/kg body wt; 800 µg · kg1 · h
1; Otsuka
America Pharmaceuticals) (42) was started at the end of
the control periods. Total body water content was kept constant during
V2-receptor blockade by iv replacement of urine losses with
150 mM glucose. Volume replacement was performed as described earlier
by use of a computer-driven, servo-control system (3, 16,
18). Urine collections were made in one 60-min period followed
by three 30-min periods. A steady-state diuresis was achieved
45-60 min after onset of the OPC-31260 infusion. Arterial blood
samples of 300 µl each were collected 1 h after OPC-31260 administration was started and at the end of the experiment.
Analytic Procedures
Urine volume was determined gravimetrically. Concentrations of sodium, potassium, and lithium in plasma and urine were analyzed with Student's unpaired t-test. 3[H]inulin and 14[C]tetraethylammonium bromide in plasma and urine were determined by dual-label liquid scintillation. The plasma concentration of aldosterone was measured by RIA using a commercial kit (Coat-A-Count Aldosterone, DPC, Los Angeles, CA). Vasopressin was extracted from plasma on C18 SEP-Pak cartridges and measured by RIA as described earlier (20).Membrane Fractionation for Immunoblotting
Two additional series of rats were prepared for semiquantitative immunoblotting. The rats were anesthetized with halothane-nitrous oxide and, in one group of animals, the right kidney was removed and immediately frozen in liquid nitrogen and stored atElectrophoresis and Immunoblotting
Samples of membrane fractions (~2 µg/lane) were run on 12% polyacrylamide minigels (Bio-Rad Mini Protean II). For each gel, an identical gel was run in parallel and subjected to Coomassie staining to assure identical loading (37). The other gel was subjected to immunoblotting. Blots were blocked with 5% milk in PBS-T (80 mM Na2HPO4, 20 mM Na2HPO4, 100 mM NaCl, 0.1% Tween 20, pH 7.5) for 1 h and incubated with affinity-purified anti-AQP2 [40 ng IgG/µl IgG (see Refs. 6, 26-28)]. The labeling was visualized with horseradish peroxidase-conjugated secondary antibody (P448; DAKO; diluted 1:3,000), using an enhanced chemiluminescence system (Amersham). Controls were prepared with replacement of the primary antibody with an antibody preabsorbed with immunizing peptide IgG, or with nonimmune IgG.Quantitation of AQP2 Expression
Enhanced chemiluminescence films with bands within the linear range were scanned (24) by using an AGFA scanner (ARCUS II). For AQP2, both the 29- and the 35- to 50-kDa band, corresponding to the nonglycosylated and the glycosylated species (36), were scanned as described earlier (12, 23, 26, 28, 37). The labeling density in cirrhotic rats was quantitated (23, 26) from blots run on a gel, along with control material taken from vehicle-treated control animals. The labeling density was corrected by densitometry of identical Coomassie-stained gels run in parallel. AQP2 labeling in samples from cirrhotic rats was expressed relative to the mean expression in the corresponding control material run on the same gel.Statistics
Data are presented as means ± SE. To evaluate the effects of V2 receptor blockade, the average value during the two 30-min control periods was compared with the average value during the last two 30-min periods during OPC-31260-induced diuresis. Within-group comparisons were analyzed with Student's paired t-test. Between-group comparisons were analyzed with Student's unpaired t-test. Differences were considered significant at the 0.05 level. ![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Body Weight Gain, Urine Production, and Sodium Balance
The average daily weight gain during the first 14 wk was significantly higher in control than in the cirrhotic rats (control: 0.63 ± 0.04 vs. cirrhosis: 0.48 ± 0.06 g/day, P < 0.05) (Fig. 1). Thereafter, the control rats showed no further weight gain from week 14 until the termination of the study at the end of week 16 (0.07 ± 0.21 g/day), whereas cirrhotic rats showed a marked increase in daily weight gain (1.27 ± 0.30 g/day). The metabolic cage study in experimental week 16 showed that the increased weight gain in the cirrhotic rats was associated with sodium retention relative to the control animals (0.81 ± 0.10 vs. 0.38 ± 0.01 mmol Na/day, P < 0.01), increased urinary concentration, as reflected by a decreased urine output (4.73 ± 0.23 vs. 9.28 ± 1.33 ml · day
|
Plasma Biochemistry
Plasma levels of vasopressin (6.4 ± 1.4 vs. 1.7 ± 0.3 pg/ml, P < 0.01) and aldosterone (6.3 ± 0.6 vs. 2.2 ± 0.3 nM, P < 0.01) were significantly increased, and plasma sodium (140.5 ± 0.8 vs. 145.6 ± 1.2 mM, P < 0.01) significantly decreased in the cirrhotic rats (Fig. 2).
|
Baseline Values for Systemic and Renal Hemodynamics and Tubular Function
Table 1 shows systemic and renal hemodynamics and tubular function during control conditions in the renal clearance experiments. The cirrhotic rats had decreased MAP, and renal function was significantly attenuated: effective renal plasma flow (ERPF), GFR, and the fractional lithium excretion were all significantly decreased, and so were V and tubular sodium and potassium handling.
|
Renal Function During IV Water Loading
Water loading (10 ml water bolus, infusion rate: 1 ml/min iv) did not affect MAP, ERPF, GFR, and the renal handling of lithium and sodium in both groups (data not shown). However, the cirrhotic rats showed marked changes in renal water handling: the time profile for the cumulated excretion of the water load was significantly delayed (Table 2), and the maximal increases in diuresis and free water clearance were significantly attenuated (maximal
|
|
Effect of V2-Receptor Blockade on Renal Water Handling
Systemic and renal hemodynamics, GFR, and the renal handling of sodium, potassium, and lithium were, as previously shown (15, 18), unchanged during acute iv treatment with the V2-receptor antagonist OPC-31260 (data not shown). V2-receptor blockade induced marked changes in the renal water handling with significant increases in V, CH2O, V/GFR, and V/CLi in both groups (Fig. 4). The increases in V and CH2O were not different in the cirrhotic and control rats. However, when expressed as a fraction of GFR or distal delivery, the aquaretic effect of OPC-31260 was significantly enhanced in the cirrhotic rats:
|
Renal Expression of AQP2 Protein
Figures 5 and 6 show immunoblots of membrane fractions (2 µg/lane) from whole kidney preparations (Fig. 5) and preparations of inner medulla (Fig. 6). As previously shown, the affinity-purified anti-AQP2 protein antibody recognizes the 29- and the 35- to 50-kDa band, corresponding to nonglycosylated and glycosylated AQP2 protein, respectively. As shown in Figs. 5A (whole kidney) and 6A (inner medulla), similar labelings of both the 29- and the 35- to 50-kDa AQP2 bands were observed in the control and the cirrhotic rats. This was confirmed by densitometry of all samples (Figs. 5B and 6B) that showed no difference in the expression of AQP2 protein between cirrhotic and control rats. Thus, despite significantly increased plasma levels of vasopressin and marked water retention, AQP2 expression remained normal in the cirrhotic rats.
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
This study was designed to elucidate renal mechanisms in the disturbed water metabolism in rats with decompensated liver cirrhosis and hyponatremia induced by chronic administration of CCl4. The animal model showed marked alterations in water homeostasis: urine production was decreased, urine osmolality increased, and the rats had decreased plasma sodium concentration and ascites. Plasma vasopressin concentrations were increased, and the rats showed an impaired ability to excrete an iv water load. The fractional aquaretic response to acute selective vasopressinV2-receptor blockade was increased, but the renal expression of AQP2 was unchanged. Together, these results shows that AQP2 expression, despite decompensation and increased plasma vasopressin levels, is unchanged in rats with CCl4-induced liver cirrhosis.
Regulation of AQP2 Expression
Vasopressin regulates water permeability in the renal collecting duct by short-term and long-term regulation. Collecting duct water permeability increases within a few minutes in response to an acute increase in plasma vasopressin concentration, and this is mediated by shuttling of AQP2 from intracellular vesicles into the apical plasma membrane via exocytosis (27, 28, 34, 41). For long-term regulation of body water, the total amount of AQP2 protein in the principal cells is increased (28), along with increased AQP2 mRNA levels (22) due, at least in part, to increased AQP2 gene transcription (30). Conversely, in the absence of vasopressin, e.g., in vasopressin-deficient homozygous Brattleboro rats, AQP2 expression is suppressed (6). From several studies it has become clear that both vasopressin-dependent and vasopressin-independent mechanisms operate to modulate AQP2 expression levels (for recent review, see Ref. 29). Long-term treatment of vasopressin-deficient Brattleboro rats with vasopressin resulted in 1) a marked increase in AQP2 expression levels, 2) increased osmotic water permeability of inner medullary collecting ducts, and 3) complete restoration of the urinary concentration defect (6). However, vasopressin-independent regulation of AQP2 also seems to be present in rats with lithium- induced nephrogenic diabetes insipidus; thirsting (or water deprivation) produces a much greater increase in AQP2 expression than 7 days of 1-desamino-8-D-arginine vasopressin (dDAVP) treatment (24). Water loading of rats with clamped high levels of plasma dDAVP causes an escape from the renal effects of dDAVP associated with a significant reduction in renal AQP2 levels (8, 9). Thirsting of rats in the presence of chronic V2-receptor blockade (OPC-31260) increases AQP2 expression levels (24). Together, these studies have given support to the view that vasopressin-independent mechanisms may play a significant role in modulating AQP2 expression levels, and several studies suggest that this pathway may be involved in various water balance disorders.AQP2 Expression in Conditions with Disturbances in Renal Water Handling
Dysregulation of AQP2 expression has been shown to be associated with several diseases or conditions with disturbances in renal water handling. Experimental studies in rats have shown that conditions with increased solute-free urine production, such as acquired nephrogenic diabetes insipidus (23), hypokalemia (25), hypercalcemia (7, 35), ureteral obstruction (12), and chronic aldosterone-receptor blockade (18), all display a significant downregulation of renal AQP2 expression. Furthermore, it has been shown that mutant, nonfunctional AQP2 was the cause of very severe non-X-linked inherited nephrogenic diabetes insipidus in humans (5). Together, this points to AQP2 dysfunction/regulation as a major common component in conditions with defects in renal concentrating ability.The role of AQP2 in conditions with extracellular volume expansion is more unclear. Rats with severe congestive heart failure associated with hyponatremia and increased plasma vasopressin levels (31, 40) have a significantly increased AQP2 expression. However, rats with nephrotic syndrome induced by pyromycin aminonucleotide (1) or adriamycin (10) have a significant downregulation of renal AQP2 expression. The mechanisms behind this downregulation is unknown.
AQP2 Expression in Liver Cirrhosis
Initial studies made in rats with severe CCl4-induced liver cirrhosis showed a significant increase in AQP2 expression (2, 13). However, we recently found a significant downregulation of AQP2 expression in rats with compensated liver cirrhosis induced by common bile duct ligation (16, 18). These rats had sodium retention, slightly increased plasma levels of vasopressin, and normal GFR, but no sign of ascites. Accordingly, Fernandez-Llama and coworkers (11) recently reported a significant downregulation of AQP2 in rats with liver cirrhosis induced by common bile duct ligation, where decompensation was induced by giving the rats free access to sweetened water. The present study showed a normal expression of AQP2 in rats with decompensated liver cirrhosis induced by CCl4 administration. The discrepancy between the present and the previously reported findings in the CCl4 model of decompensated liver cirrhosis is unclear. One possible explanation could be that the initial studies (2, 13) showing increased AQP2 expression were made in rats with very severe water disturbances in the terminal state of the disease. Unfortunately, no information about renal function in terms of renal perfusion, GFR, or segmental tubular function were reported in these studies.Our present observation, that rats with decompensated cirrhosis developed water retention with the formation of ascites and decreased plasma sodium concentration (hyponatremia) in the absence of increases in the AQP2 expression, raises the question of how water retention occurs in this model of liver cirrhosis. We recently demonstrated that rats with compensated liver cirrhosis (induced by common bile duct ligation) and significantly decreased AQP2 expression have increased furosemide-sensitive sodium reabsorption and tubular hypertrophy in the thick ascending limb of Henle's (TAL) (14-16). These functional and structural changes were associated with sodium retention and an increased interstitial sodium concentration in the renal medulla (16). In addition, we have shown that rats with CCl4-induced cirrhosis with ascites and hyponatremia have the same functional changes in the TAL as the common bile duct-ligated rats (19). Furthermore, the present study demonstrates that the fractional water excretion in response to acute V2-receptor blockade is significantly increased in the CCl4 rats, suggesting that the vasopressin-sensitive water reabsorption capacity is increased in these water-retaining rats. Therefore, we propose that the increased sodium reabsorption in the TAL induces an increased corticopapillary interstitial osmotic gradient and thus increases the driving force for collecting duct water reabsorption. The lack of increased AQP2 expression despite increased plasma vasopressin levels could then be a compensatory mechanism aimed at limiting excessive collecting duct water reabsorption and thereby preventing avid water intoxication. The mechanism behind such a compensatory "escape" from vasopressin stimulation in the collecting ducts is, however, unknown.
Summary
In summary, the present study demonstrates that rats with CCl4-induced liver cirrhosis and increased plasma vasopressin levels decompensate with the formation of decreased plasma sodium concentration and ascites in the absence of changes in the renal expression of AQP2. However, functional studies with acute selective vasopressinV2-receptor blockade in chronic catheterized rats indicate that the vasopressin-sensitive water reabsorption capacity is increased in the cirrhotic rats. Together, these results indicates that vasopressin-mediated water reabsorption in the collecting ducts is increased in rats with CCl4-induced cirrhosis despite an unchanged expression of AQP2. ![]() |
ACKNOWLEDGEMENTS |
---|
The technical assistance of Anette Francker, Anette Nielsen, Iben Nielsen, Bettina Sandborg, Mette Vistisen, and Annette Blak Rasmussen is acknowledged. We gratefully acknowledge Dr. J. Warberg for performing the plasma vasopressin analyses.
![]() |
FOOTNOTES |
---|
This work received financial support from the Danish Medical Research Council, the Novo Nordic Foundation, the P. Carl Petersen Foundation, the Eva and Robert Voss Hansen Foundation, the Ruth Kønig-Petersen Foundation, the Knud Øster-Jørgensen Foundation, the Helen and Ejnar Bjørnow Foundation, the Karen Elise Jensen Foundation, the Aage Thuesen Bruun Foundation, the University of Aarhus, and the EU Commission (EU-Biotech programme and EU-TMR programme). Part of this study was presented in preliminary form at the annual meeting of the Federation of American Societies for Experimental Biology, Experimental Biology 99, Washington DC, April 17-21, 1999.
Address for reprint requests and other correspondence: T. E. N. Jonassen, Dept. of Pharmacology, The Panum Institute, Univ. of Copenhagen, 3 Blegdamsvej, Bldg. 18.6, DK-2200 Copenhagen N, Denmark (E-mail: fitj{at}farmakol.ku.dk).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 20 February 2000; accepted in final form 21 August 2000.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Apostol, E,
Ecelbarger CA,
Terris J,
Bradford AD,
Andrews P,
and
Knepper MA.
Reduced renal medullary water channel expression in puromycin aminonucleoside-induced nephrotic syndrome.
J Am Soc Nephrol
8:
15-24,
1997[Abstract].
2.
Asahina, Y,
Izumi N,
Enomoto N,
Sasaki S,
Fushimi K,
Marumo F,
and
Sato C.
Increased gene expression of water channel in cirrhotic rat kidneys.
Hepatology
21:
169-173,
1995[ISI][Medline].
3.
Burgess, WJ,
Shalmi M,
Petersen JS,
Plange-Rhule J,
Balment RJ,
and
Atherton J.
A novel-computer-driven, servo-controlled fluid replacement technique and its application to renal function studies in conscious rats.
Clin Sci (Colch)
85:
129-137,
1993[ISI][Medline].
4.
Christensen, BM,
Marples D,
Jensen UB,
Frøkiær J,
Sheikh-Hamad D,
Knepper MA,
and
Nielsen S.
Short-term effects of vasopressin (V2)-receptor antagonist treatment on AQP2 expression and subcellular distribution in rat kidney.
Am J Physiol Renal Physiol
275:
F285-F297,
1998
5.
Deen, PM,
Verdijk MA,
Knoers NV,
Wieringa B,
Monnens LA,
and
van Oost BA.
Requirement of human renal water channel aquaporin-2 for vasopressin-dependent concentration of urine.
Science
264:
92-95,
1994[ISI][Medline].
6.
DiGiovanni, SR,
Nielsen S,
Christensen EI,
and
Knepper MA.
Regulation of collecting duct water channel expression by vasopressin in Brattleboro rat.
Proc Natl Acad Sci USA
92:
8984-8988,
1994.
7.
Earm, JH,
Christensen BM,
Marples D,
Frøkiær J,
Han J,
Knepper MA,
and
Nielsen S.
Decreased aquaporin-2 water channel expression in kidney inner medulla of hypercalcemic rats.
J Am Soc Nephrol
9:
2181-2193,
1998[Abstract].
8.
Ecelbarger, CA,
Chou CL,
Lee AJ,
DiGiovanni SR,
Verbalis JG,
and
Knepper MA.
Escape from vasopressin-induced antidiuresis: role of vasopressin resistance of the collecting duct.
Am J Physiol Renal Physiol
274:
F1161-F1166,
1998
9.
Ecelbarger, CA,
Nielsen S,
Olson BR,
Murase T,
Baker EA,
Knepper MA,
and
Verbalis JG.
Role of renal aquaporins in escape from vasopressin-induced antidiuresis in rat.
J Clin Invest
99:
1852-1863,
1997
10.
Fernandez-Llama, P,
Andrews P,
Nielsen S,
Ecelbarger CA,
and
Knepper MA.
Impaired aquaporin and urea transporter expression in rats with adriamycin-induced nephrotic syndrome.
Kidney Int
53:
1244-1253,
1998[ISI][Medline].
11.
Fernandez-Llama, P,
Turner R,
DiBona G,
and
Knepper MA.
Renal expression of aquaporins in liver cirrhosis induced by chronic common bile duct ligation in rats.
J Am Soc Nephrol
10:
1950-1957,
1999
12.
Frøkjær, J,
Marples D,
Knepper MA,
and
Nielsen S.
Bilateral ureteral obstruction downregulates expression of vasopressin-sensitive AQP-2 water channel in rat kidney.
Am J Physiol Renal Fluid Electrolyte Physiol
270:
F657-F668,
1996
13.
Fujita, N,
Ishikawa SE,
Sasaki S,
Fujisawa G,
Fushimi K,
Marumo F,
and
Saito T.
Role of water channel AQP-CD in water retention in SIADH and cirrhotic rats.
Am J Physiol Renal Fluid Electrolyte Physiol
269:
F926-F931,
1995
14.
Jonassen, TEN,
Christensen S,
Sørensen AM,
Marcussen N,
Flyvbjerg A,
Andreasen F,
and
Petersen JS.
Effects of chronic octreotide treatment on renal changes during cirrhosis in rats.
Hepatology
29:
1387-1395,
1999[ISI][Medline].
15.
Jonassen, TEN,
Marcussen N,
Haugan K,
Skyum H,
Christensen S,
Andreasen F,
and
Petersen JS.
Functional and structural changes in the thick ascending limb of Henle's loop in rats with liver cirrhosis.
Am J Physiol Regulatory Integrative Comp Physiol
273:
R568-R577,
1997
16.
Jonassen, TEN,
Nielsen S,
Christensen S,
and
Petersen JS.
Decreased vasopressin-mediated renal water reabsorption in rats with compensated liver cirrhosis.
Am J Physiol Renal Physiol
275:
F216-F225,
1998
17.
Jonassen, TEN,
Petersen JS,
Sørensen AM,
Andreasen F,
and
Christensen S.
Aldosterone receptor blockade inhibits increased furosemide- sensitive sodium reabsorption in rats with liver cirrhosis.
J Pharmacol Exp Ther
287:
931-936,
1998
18.
Jonassen, TEN,
Promeneur D,
Christensen S,
Petersen JS,
and
Nielsen S.
Decreased vasopressin-mediated renal water reabsorption in rats with chronic aldosterone-receptor blockade.
Am J Physiol Renal Physiol
278:
F246-F256,
2000
19.
Jonassen, TEN,
Sørensen AM,
Petersen JS,
Andreasen F,
and
Christensen S.
Increased natriuretic efficiency of furosemide in rats with carbon tetrachloride induced liver cirrhosis.
Hepatology
31:
1224-1230,
2000[ISI][Medline].
20.
Kjær, A,
Knigge U,
and
Warberg J.
Dehydration-induced release of vasopressin involves activation of hypothalamic histaminergic neurons.
Endocrinology
135:
675-681,
1994[Abstract].
21.
Leyssac, PP,
Frederiksen O,
Holstein-Rathlou NH,
Alfrey AC,
and
Christensen P.
Active lithium transport by the rat renal proximal tubule: a micropuncture study.
Am J Physiol Renal Fluid Electrolyte Physiol
267:
F86-F93,
1994
22.
Ma, T,
Hasegawa H,
Skach WR,
Frigeri A,
and
Verkman AS.
Expression, functional analysis, and in situ hybridization of a cloned rat kidney collecting duct water channel.
Am J Physiol Cell Physiol
266:
C189-C197,
1994
23.
Marples, D,
Christensen S,
Christensen EI,
Ottesen PO,
and
Nielsen S.
Lithium-induced downregulation of aquaporin-2 water channel expression in rat kidney medulla.
J Clin Invest
95:
1838-1845,
1995[ISI][Medline].
24.
Marples, D,
Christensen BM,
Frøkjær J,
Knepper MA,
and
Nielsen S.
Dehydration reverses vasopressin antagonist-induced diuresis and aquaporin-2 downregulation in rats.
Am J Physiol Renal Physiol
275:
F400-F409,
1998
25.
Marples, D,
Frøkiær J,
Dørup J,
Knepper MA,
and
Nielsen S.
Hypokalemia-induced downregulation of aquaporin-2 water channel expression in rats kidney medulla and cortex.
J Clin Invest
97:
1960-1968,
1996
26.
Marples, D,
Knepper MA,
Christensen EI,
and
Nielsen S.
Redistribution of aquaporin-2 water channels induced by vasopressin in rat kidney inner medulla collecting duct.
Am J Physiol Cell Physiol
269:
C655-C664,
1995[Abstract].
27.
Nielsen, S,
Chou CL,
Marples D,
Christensen EI,
Kishore BK,
and
Knepper MA.
Vasopressin increases water permeability of kidney collecting duct by inducing translocation of aquaporin-CD channels to plasma membrane.
Proc Natl Acad Sci USA
92:
1013-1017,
1995[Abstract].
28.
Nielsen, S,
DiGiovanni SR,
Christensen EI,
Knepper MA,
and
Harris HW.
Cellular and subcellular immunolocalization of vasopressin-regulated water channel in rat kidney.
Proc Natl Acad Sci USA
90:
11663-11667,
1993[Abstract].
29.
Nielsen, S,
Frøkjær J,
and
Knepper MA.
Renal aquaporins: key roles in water balance and water balance disorders.
Curr Opin Nephrol Hypertens
7:
509-516,
1998[ISI][Medline].
30.
Nielsen, S,
Marples D,
Frøkier J,
Knepper MA,
and
Agre P.
The aquaporin family of water channels in kidney: an update on physiology and pathophysiology of aquaporin-2.
Kidney Int
49:
1718-1723,
1996[ISI][Medline].
31.
Nielsen, S,
Terris J,
Andersen D,
Ecelbarger C,
Frøkiær J,
Jonassen T,
Marples D,
Knepper MA,
and
Petersen JS.
Congestive heart failure in rats is associated with increased expression and targeting of aquaporin-2 water channel in collecting duct.
Proc Natl Acad Sci USA
94:
5450-5455,
1997
32.
Petersen, JS,
and
Christensen S.
Superiority of tetraethylammonium versus p-aminohippurate as a marker for renal plasma flow during furosemide diuresis.
Renal Physiol
10:
102-109,
1987[ISI][Medline].
33.
Petersen, JS,
Shalmi M,
Lam HR,
and
Christensen S.
Renal response of furosemide in conscious rats: effects of acute instrumentation and peripheral sympathectomy.
J Pharmacol Exp Ther
258:
1-7,
1991[Abstract].
34.
Sabolic, I,
Katsura T,
Verbavatz JM,
and
Brown D.
The AQP2 water channel: effect of vasopressin treatment, microtubule disruption, and distribution in neonatal rats.
J Membr Biol
143:
165-175,
1995[ISI][Medline].
35.
Sands, JM,
Flores FX,
Kato A,
Baum MA,
Brown EM,
Ward DT,
Hebert SC,
and
Harris HW.
Vasopressin-elicidated water and urea permeabilities are altered in IMCD in hypercalcemic rats.
Am J Physiol Renal Physiol
274:
F978-F985,
1998
36.
Sasaki, S,
Fushimi K,
Saito H,
Uchida S,
Ishibashi K,
Kuwahara M,
Ikeuchi T,
Inui K,
Nakajima K,
Watanabe TX,
and
Marumo F.
Cloning, characterization, and chromosomal mapping of human aquaporin of collecting duct.
J Clin Invest
93:
1250-1256,
1994[ISI][Medline].
37.
Terris, J,
Ecelbarger CA,
Nielsen S,
and
Knepper MA.
Long-term regulation of four renal aquaporins in rats.
Am J Physiol Renal Fluid Electrolyte Physiol
271:
F414-F422,
1996
38.
Thomsen, K,
and
Shirley DG.
The validity of lithium clearance as an index of sodium and water delivery from the proximal tubules.
Nephron
77:
125-138,
1997[ISI][Medline].
39.
Ushida, S,
Sasaki S,
Fushimi K,
and
Marumo F.
Isolation of human aquaporin-CD gene.
J Biol Chem
269:
23451-23455,
1994
40.
Xu, DI,
Martin PY,
Ohara M,
St. John J,
Pattison T,
Meng X,
Morris K,
Kim JK,
and
Schrier RW.
Upregulation of aquaporin-2 water channel expression in chronic heart failure in rat.
J Clin Invest
99:
1500-1505,
1997
41.
Yamamoto, T,
Sasaki S,
Fushimi K,
Ishibashi K,
Yaoita E,
Kawasaki K,
Marumo F,
and
Kihara I.
Vasopressin increases AQP-CD water channel in apical membrane of collecting duct cells in Brattleboro rats.
Am J Physiol Cell Physiol
268:
C1546-C1551,
1995
42.
Yamamura, Y,
Ogawa H,
Yamashita H,
Chihara T,
Miyamoto H,
Nakamura S,
Onogawa T,
Yamashita T,
Hosokawa T,
Mori T,
Tominaga M,
and
Yabuuchi Y.
Characterization of a novel aquaretic agent, OPC-31260, as an orally effective, nonpeptide vasopressin V2 receptor antagonist.
Br J Pharmacol
105:
787-791,
1992[Abstract].