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Journal of the American Heart Association: Cardiovascular and Cerebrovascular Disease logoLink to Journal of the American Heart Association: Cardiovascular and Cerebrovascular Disease
. 2020 May 9;9(10):e014950. doi: 10.1161/JAHA.119.014950

Glucocorticoids Reverse Diluted Hyponatremia Through Inhibiting Arginine Vasopressin Pathway in Heart Failure Rats

Xiaoran Zhu 1,2, Yaomeng Huang 1, Shuyu Li 1,3, Ning Ge 4, Tongxin Li 1, Yu Wang 1, Kunshen Liu 1, Chao Liu 1,✉
PMCID: PMC7660850  PMID: 32390535

Abstract

Background

Arginine vasopressin dependent antidiuresis plays a key role in water‐sodium retention in heart failure. In recent years, the role of glucocorticoids in the control of body fluid homeostasis has been extensively investigated. Glucocorticoid deficiency can activate V2R (vasopressin receptor 2), increase aquaporins expression, and result in hyponatremia, all of which can be reversed by glucocorticoid supplement.

Methods and Results

Heart failure was induced by coronary artery ligation for 8 weeks. A total of 32 rats were randomly assigned to 4 groups (n=8/group): sham surgery group, congestive heart failure group, dexamethasone group, and dexamethasone in combination with glucocorticoid receptor antagonist RU486 group. An acute water loading test was administered 6 hours after drug administration. Left ventricular function was measured by a pressure‐volume catheter. Protein expressions were determined by immunohistochemistry and immunoblotting. The pressure‐volume loop analysis showed that dexamethasone improves cardiac function in rats with heart failure. Western blotting confirmed that dexamethasone remarkably reduces the expressions of V2R, aquaporin 2, and aquaporin 3 in the renal‐collecting ducts. As a result of V2R downregulation, the expressions of glucocorticoid regulated kinase 1, apical epithelial sodium channels, and the furosemide‐sensitive Na‐K‐2Cl cotransporter were also downregulated. These favorable effects induced by dexamethasone were mostly abolished by the glucocorticoid receptor inhibitor RU486, indicating that the aforementioned effects are glucocorticoid receptor mediated.

Conclusions

Glucocorticoids can reverse diluted hyponatremia via inhibiting the vasopressin receptor pathway in rats with heart failure.

Keywords: aquaporins, cardiorenal syndrome, glucocorticoids, heart failure, hyponatremia, vasopressin

Subject Categories: Animal Models of Human Disease

Nonstandard Abbreviations and Acronyms

AQP2

aquaporin 2

AQP3

aquaporin 3

AVP

arginine vasopressin

ENaC

epithelial sodium channels

GR

glucocorticoid receptor

HF

heart failure

NKA

Na+/K+‐ATPase

NKCC2

furosemide‐sensitive Na–K–2Cl cotransporter

SGK1

serum and glucocorticoid regulated kinase 1

Clinical Perspective

What Is New?

  • In this study, we demonstrate that glucocorticoids can reverse diluted hyponatremia by increasing renal water excretion in rats with heart failure with acute water load.

  • The renal diuresis enhancing effects induced by glucocorticoids are mediated by inhibiting the vasopressin receptor 2 pathway.

  • Recent clinical studies demonstrated that glucocorticoids could enhance renal water excretion in patients with heart failure.

What Are the Clinical Implications?

  • Our research reveals that glucocorticoids can promote water–sodium excretion and improve cardiac function.

  • This provides a theoretical basis for the application of glucocorticoids in the treatment of heart failure with diluted hyponatremia.

Heart failure (HF) is a pathophysiological state characterized by ventricular dysfunction and water and sodium retention. Patients with HF may present with water retention, increased water intake, or both, together with excessive sodium retention, which may lead to hyponatremia. In patients with HF, arginine vasopressin (AVP) V2R (vasopressin receptor 2) antagonists effectively correct impaired urinary diluting capacity, increasing renal free water excretion and reversing hyponatremia.1 This suggests that V2R exerts a pivotal role in hyponatremia.

V2R is expressed in the basolateral membrane of distal tubules and collecting ducts. It plays a vital role in the maintenance of water–sodium homeostasis and blood volume regulation.2 AVP signals through V2R to regulate the expression of AQP2 (aquaporin 2) in the apical membrane and AQP3 (aquaporin 3) in the basolateral membrane.3 V2R activation increases the shuttling of AQP2 and AQP3 to the apical surface and basolateral membrane, respectively, leading to increased water permeability (ie, water absorption). V2R activation also leads to sodium reabsorption. On the other hand, SGK1 (serum and glucocorticoid regulated kinase 1) regulates the transport of various sodium channels. AVP and SGK1 increase the protein abundance and/or activity of certain ion channels, such as epithelial sodium channels (ENaC),4, 5 NKCC2 (furosemide‐sensitive Na–K–2Cl cotransporter), and NKA (Na+/K+‐ATPase). During the past several decades, the causal relationship between hyponatremia and glucocorticoid deficiency has become well established both in the clinical setting and in animal studies. Glucocorticoid deficiency increases AVP release, activates V2R, upregulates AQP2 expression, impairs renal free water excretion, and leads to hyponatremia,6, 7, 8 all of which can be reversed by glucocorticoid supplement therapy. Importantly, recent clinical trials on HF have indicated that glucocorticoid treatment as an add‐on therapy could potentiate renal diuresis, improve renal function, and alleviate hyponatremia.9, 10, 11, 12 The mechanisms underlying the renal protective effects induced by glucocorticoids are not fully understood. Here we test the hypothesis that glucocorticoids potentiate renal excretion of free water, thereby correcting dilutive hyponatremia by inhibiting the V2R pathway.

METHODS

The data, analytic methods, and study materials will be made available upon request to other researchers for purposes of reproducing the results or replicating the procedure. All experimental protocols were approved by the Ethics Review Committee for Animal Experimentation of Hebei Medical University.

An extended description of the methods can be found in Data S1.

Chronic HF Model Preparation

The CHF rat model of myocardial infarction was established by coronary artery ligation (left ventricular ejection fraction<45%) as previously described.13 An acute water loading test was performed 8 weeks after surgery. A total of 32 rats were randomly distributed into 4 groups (n=8/group): sham surgery, chronic HF (CHF), dexamethasone (1 mg/kg, intramuscular), dexamethasone in combination with the glucocorticoid receptor (GR) antagonist RU486 (mifepristone 100 mg/kg, subcutaneously 1 hour before dexamethasone administration). Exact numbers for each part of the experiment are marked in the annotated section of the Figures. The detailed experimental process is shown in Figure S1.

Cardiac Hemodynamics Measurement

Cardiac function was assessed 6 hours after water loading using a rat pressure‐volume catheter (SPR‐869; Millar Instruments, Houston, TX) and an MPVS pressure‐volume conductance system (Millar Instruments) coupled to a Powerlab A/D converter (PL3508, AD Instruments, New South Wales, Australia), as previously described.14

Hemodynamic parameters were computed according to the protocol published previously.15 The details can be found in Data S1. The end‐systolic pressure‐volume relationship describes the maximal pressure developed by the ventricle at different ventricular filling volumes. The end‐systolic pressure‐volume relationship becomes steeper and shifts to the left as inotropy (contractility) increases. The maximal slope of systolic pressure increment occurs early during isovolumic contraction. It is sensitive to the inotropic state and correlates with cardiac contractility. However, it is load dependent. Preload recruitable stroke work is determined by the linear regression of stroke work with the end‐diastolic volume, which provides a contractility index that is insensitive to preload by definition, but it is also remarkably insensitive to changes in afterload at the expense of lower inotropic sensitivity. The isovolumic relaxation constant (tau) represents the exponential decay of the ventricular pressure during isovolumic relaxation. Tau is a preload‐independent measure of isovolumic relaxation. With an increased tau (ie, slowing of relaxation), a higher mean left atrial pressure may be required to achieve normal filling volumes. Preload, also known as the left ventricular end‐diastolic pressure, is the amount of ventricular stretch (ie, volume overload) at the end of diastole. The greater the preload, the more pressure is available for the next cardiac contraction.

AVP Measurement

The EDTA‐treated blood samples were centrifuged (3000g, 10 minutes) at 4°C and stored at −80°C. Plasma AVP was determined by enzyme‐linked immunosorbent assay kits (R&D Systems, Minneapolis, MN).

Western Blot

The inner medulla of the kidneys was quickly removed and placed in liquid nitrogen. Membrane proteins affecting water and sodium excretion, such as V2R, AQP2, AQP3, α‐ENaC, NKA, and SGK1 were assessed by Western blot analysis. Protein bands were visualized and analyzed using an Odyssey system (LI‐COR, Lincoln, NE). Band intensities were normalized by total plasma membrane protein quantification (Bio‐Rad, Hercules, CA).16

Immunohistochemistry

Membrane proteins, such as V2R and AQP2, were visualized by immunohistochemistry. Three fields from each section were randomly selected using a DP73 microscope (Olympus, Tokyo, Japan).

Statistical Analysis

All statistical analyses were performed using SPSS software (SPSS version 20.0; IBM Corp, Armonk, NY). The results are expressed as mean±SEM. The data in Figures 1 and 2 were statistically analyzed using nonparametric tests (Kruskal‐Wallis). For Western blot data with equal variance, 1‐way ANOVA was used followed by LSD post hoc comparisons. The Kruskal‐Wallis test was used for groups with unequal variance. P>0.05 means no statistical difference; 0.05>P>0.01 means a statistical difference; P>0.01 means the statistical difference is extremely significant.

Figure 1. The effect of DEX on renal water excretion in rats with heart failure (n=6–8).

Figure 1

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A, Effect of DEX on cumulative urinary volume. B, Effect of DEX on plasma sodium concentration. C, Effect of DEX on plasma chlorine level. D, Effect of DEX on POSm. E, Effect of DEX on total urinary sodium excretion. F, Effect of DEX on UOsm. G, Plasma AVP levels were compared between the 4 groups. AVP indicates arginine vasopressin; CHF, congestive heart failure group; CON, sham surgery group; DEX, dexamethasone group; DEX+RU486, dexamethasone in combination with glucocorticoid receptor antagonist RU486 group; NS, no statistical difference; POSm, plasma osmotic pressure; and UOsm, urinary osmotic pressure. *P<0.05, **P<0.01 for CHF vs CON; # P<0.05, ## P<0.01 for DEX vs CHF; & P<0.05, && P<0.01 for DEX+RU486 vs DEX.

Figure 2. The effect of DEX on cardiac function in rats with heart failure (n=6–8).

Figure 2

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A, Effect of DEX on pressure‐volume loops. B, Effect of DEX ESPVR. C, Effect of DEX on +dP/dtmax. D, Effect of DEX on Tau. E, Effect of DEX on PRSW. F, Effect of DEX on LVEDP. Data were obtained with a Millar Instruments (Houston, TX) pressure‐volume conductance catheter system. CHF indicates congestive heart failure group; CON, sham surgery group; DEX, dexamethasone group; DEX+RU486, dexamethasone in combination with glucocorticoid receptor antagonist RU486 group; +dP/dtmax, maximal slope of systolic pressure increment; ESPVR, end‐systolic pressure‐volume relationship; LVEDP, left ventricular end‐diastolic pressure; NS, no statistical difference; PRSW, preload recruitable stroke work; and Tau, isovolumic relaxation constant. *P<0.05; **P<0.01 for CHF vs CON; # P<0.05; ## P<0.01 for DEX vs CHF; & P<0.05; && P<0.01 for DEX+RU486 vs DEX.

RESULTS

Physiological Data

In the acute water loading test, renal water excretion was dramatically impaired in the CHF rats compared with that in normal controls. As a result, the CHF rats exhibited acute water loading–induced hyponatremia. It is noteworthy that dexamethasone pretreatment dramatically increased renal diuresis during the study period (Figure 1A), thereby successfully preventing or reversing acute water load–induced hyponatremia (Figure 1B and 1C). Moreover, dexamethasone pretreatment restored acute water load–induced plasma osmolality in the HF rats (Figure 1D). It is of note that dexamethasone‐induced diuresis was accompanied by increased natriuresis and osmolality (Figure 1E and 1F). In addition, despite the normal plasma osmolality and serum sodium levels, dexamethasone pretreatment inhibited circulating AVP levels in the CHF rats subjected to acute water load (Figure 1G). Except for AVP levels, the beneficial effects of dexamethasone pretreatment were abolished by RU486, a GR antagonist, which indicates that those effects are GR mediated.

Cardiac Hemodynamic Measurements and Pressure‐Volume Loops

We investigated the effects of dexamethasone on left ventricular function in rats with HF with the Millar pressure‐volume catheter.

Figure 2A shows typical changes in the left ventricle pressure‐volume loop throughout the cardiac cycle in the 4 groups. The data showed that the rats with CHF had a much lower end‐systolic pressure‐volume relationship (red line in the loops) than those in the normal controls. Dexamethasone restored end‐systolic pressure‐volume relationship in the rats with CHF (Figure 2A and 2B). There were no differences in the maximal slope of systolic pressure increment or preload recruitable stroke work between the 4 groups (Figure 2C and 2D). The data also indicated that the rats with CHF had an increased tau (ie, slowing of relaxation) compared with those of the normal controls, and dexamethasone could remarkably decrease tau (Figure 2E). It is of note that acute water load resulted in a dramatic increase of left ventricular end‐diastolic pressure in the rats with CHF, and left ventricular end‐diastolic pressure was decreased by dexamethasone (Figure 2F). These favorable effects induced by dexamethasone were abolished by RU486.

V2R Expression in the Inner Medulla

In the kidney, water reabsorption is mainly regulated by AVP binding to V2R, which is mainly expressed in the basolateral membrane of the collecting ducts. To test the effect of dexamethasone administration on V2R, we measured V2R expression in the collecting ducts. The Western blot result showed that the HF rats had a higher V2R expression than the normal controls. However, dexamethasone treatment decreased V2R expression in the collecting ducts of the rats with HF. The impact of dexamethasone on V2R expression was blocked by the GR antagonist RU486 (Figure 3A). Immunohistochemistry also confirmed the downregulating effect of dexamethasone on V2R expression in the inner medullary collecting duct basolateral membrane in the rats with HF (Figure 3B and 3C).

Figure 3. The effect of DEX on V2R in the kidney inner medulla by Western bolt and immunohistochemistry.

Figure 3

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A, Western blotting with anti‐V2R antibodies was carried out using inner medulla homogenates from 4 groups of rats (40 μg/lane, n=5). Densitometric analysis of V2R bands (≈42 kDa) were normalized for the stain‐free image of total plasma membrane protein abundance in each fraction. The relative expression analysis was much stronger in the rats with CHF and weaker in the DEX rats. B, Immunohistochemistry localization of V2R in the kidney inner medulla. V2R was expressed in the basolateral membrane of the collecting tube. DEX significantly inhibited the expression of V2R. Representative images are shown. AVP indicates arginine vasopressin; CHF, congestive heart failure group; CON, sham surgery group; DEX, dexamethasone group; DEX+RU486, dexamethasone in combination with glucocorticoid receptor antagonist RU486 group; and V2R, vasopressin receptor 2. *P<0.05 for CHF vs CON; # P<0.05 for DEX vs CHF; & P<0.05 for DEX+RU486 vs DEX. (Magnification ×100, bar=200 μm; magnification ×400, bar=50 μm.)

Expression of Aquaporins in the Inner Medulla

Activation of V2R increases AQP2 and AQP3 shuttling to the apical surface and basolateral membrane, respectively, thereby leading to water absorption. To determine the effect of dexamethasone on AQP2 and AQP3, we measured their expression using Western blotting and immunohistochemistry. We found that both AQP2 (28 kDa) and AQP3 (32 kDa) were increased in the collecting ducts of the rats with HF compared with the levels in normal controls and that these increases were attenuated by dexamethasone administration (Figure 4A and 4B).17 Immunohistochemistry confirmed the downregulating effect of dexamethasone on AQP2 in the inner medullary collecting duct apical membrane and on AQP3 in the basolateral membrane in the rats with HF (Figure 4C and 4D).

Figure 4. The effect of DEX on the expression of aquaporins in CHF rats.

Figure 4

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A, AQP2 expression in the membrane protein from inner medulla homogenates (30 μg/lane, n=4). Immunoblots showed a band at 28 kDa and a glycosylated protein band between 35 to 45 kDa. A stain‐free image of total membrane protein imaging was visualized on Criterion TGX Stain‐Free. Relative expression analyses of the data are demonstrated in the 4 different groups. B, AQP3 expression in the membrane protein using total protein normalization (30 μg/lane, n=5). Immunoblots showed a band at 32 kDa and a glycosylated protein band between 40 and 55 kDa. C, Immunohistochemistry for AQP2 expression in the inner medullary collecting duct apical membrane. D, Immunohistochemistry for AQP3 expression in the inner medullary collecting duct basolateral membrane. AQP2 indicates aquaporin 2; AQP3, aquaporin 3; CHF, congestive heart failure group; CON, sham surgery group; DEX, dexamethasone group; and DEX+RU486, dexamethasone in combination with glucocorticoid receptor antagonist RU486 group. *P<0.05, **P<0.01 for CHF vs CON; # P<0.05, ## P<0.01 for DEX vs CHF; & P<0.05 for DEX+RU486 vs DEX. (Magnification ×100, bar=200 μm; magnification ×400, bar=50 μm).

SGK1 and Sodium Channel Expression in the Inner Medulla

In HF, V2R activation increases the protein abundance and/or activity of ENaC and NKCC2 via the SGK1 pathway, thereby increasing sodium reabsorption. We found that the HF rats had higher SGK1 expressions than the normal controls, which was inhibited by dexamethasone (Figure S2). We also investigated the effect of dexamethasone pretreatment on ENaC and NKCC2, which express in the collecting ducts. We found that the HF rats had higher protein expressions of α‐ENaC (Figure 5A) and NKCC2 (Figure 5B) than normal controls. Dexamethasone treatment downregulated the expression of both sodium channels. Immunohistochemistry confirmed our findings and the localization of these sodium channels (Figure 5C and 5D). However, dexamethasone had no impact on NKA in the inner medullary collecting duct of rats with HF (Figure S3).

Figure 5. The effect of DEX on the expression of sodium channels in CHF rats.

Figure 5

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A, α‐ENaC (85 kDa) expression from the inner medullary collecting duct (50 μg/lane, n=4). Total protein normalization was used to quantify the results. B, NKCC2 (120 kDa) expression in the membrane protein using total protein normalization (30 μg/lane, n=4). C, Representative immunostaining image for ENaC expressed in the apical membrane of the inner medullary collecting duct. D, Representative immunostaining image for NKCC2 expressed in the apical membrane of the inner medullary collecting duct. α‐ENaC indicates α‐epithelial sodium channels; CHF, congestive heart failure group; CON, sham surgery group; DEX, dexamethasone group; and DEX+RU486, dexamethasone in combination with glucocorticoid receptor antagonist RU486 group; NKCC2, furosemide‐sensitive Na–K–2Cl cotransporter; and NS, no statistical difference. *P<0.05 for CHF vs CON; # P<0.05 for DEX vs CHF; & P<0.05 for DEX+RU486 vs DEX. (Magnification ×100, bar=200 μm; magnification ×400, bar=50 μm.

DISCUSSION

Our study showed that pretreating HF rats with glucocorticoids significantly increased the ability of the kidneys to excrete free water, producing a strong diuretic effect and reversing acute water load–induced dilutive hyponatremia. This protective effect of glucocorticoids is associated with the inhibition of the V2R pathway.

In the kidney, AVP and its primary receptor, V2R, play a critical role in body water homeostasis by influencing renal water excretion.18 Its release is triggered by low effective blood volume and hypernatremia.19 AVP causes free water absorption by activating V2R on the basolateral surface of the principal cells in the collecting duct. AQP2 water channels are critical for this cascade by allowing water molecules to cross the apical membrane of the principal cells in response to the osmotic gradient caused by the countercurrent urine‐concentrating mechanism.20 Simultaneously, AQP3 expression is increased in the basal membrane, allowing the absorbed water to cross from the basal membrane into the vessel.21, 22 V2R activation in the basolateral membrane increases water permeability through aquaporin water channels and stimulates sodium reabsorption through SGK1, which modulates a wide variety of transporters, such as the ENaC and NKCC2.23, 24 Therefore, V2R activation is an important water and sodium retention mechanism in HF. In systolic HF, reduced stroke volume accompanied by decreased systemic arterial pressure and renal perfusion activates the sympathetic nervous system, the renin–angiotensin–aldosterone system, and the AVP system. The water‐handling ability of the kidney is subsequently reduced. Consistently, our investigation showed that rats with systolic HF exhibited increased V2R expression on the basolateral surface of the principal cells in the collecting duct as well as SGK1 overexpression. Consequently, renal water and sodium excretion would increase dramatically, thereby reversing acute water load–induced hyponatremia. Our findings indicate that, in HF, the V2R pathway is inhibited by dexamethasone administration in the acute water loading test. The benefits of dexamethasone administration are abolished by the GR antagonist RU486, suggesting that such effects are mediated by GR.

The effect of glucocorticoids on AQP2 in renal cells has been widely studied both in vitro and in vivo. A paradoxical phenomenon has been observed in which glucocorticoids consistently increase AQP2 expression in renal cells in vitro25, 26 whereas they decrease AQP2 expression in renal cells in vivo.27, 28 In our study, dexamethasone treatment was associated with a reduction in V2R expression, a decrease in AQP2 and AQP3, and an increase in renal water exertion. These findings are consistent with previous studies in vivo.27, 28 Discrepancies between in vitro and in vivo results may occur because molecular biological studies in vitro may overlook the importance of competing or compensatory events occurring in vivo. Our previous findings support this view. We found that glucocorticoids can upregulate the expression of NPR‐A (natriuretic peptide receptor A) in the inner medullary collecting duct, both in vitro and in vivo, thereby potentiating renal responsiveness to natriuretic peptides.29 Activation of NPR‐A in collecting tubule cells could inhibit V2R activity.13 In addition, the effect of glucocorticoids on AQP2 was analyzed in vitro in nonpolarized cells and in vivo in polarized renal cells.30 The different cell context may have also contributed to the discrepancy. Attempts to resolve these actions (sometimes through countervailing actions) into specific tubular components are confounded by the following 2 phenomena: the pleiotropic effects of glucocorticoids and the promiscuity of steroid receptor–ligand interactions.

The GR and mineralocorticoid receptor share high in vitro affinity for both steroid classes. However, the in vivo specificity of the mineralocorticoid receptor for its cognate ligand is conferred by the prereceptor metabolism of glucocorticoids by 11βHSD2 (11 β‐hydroxysteroid dehydrogenase 2). 11βHSD2 converts glucocorticoids into physiologically inactive 11‐keto glucocorticoid derivatives. Thus, 11βHSD2 confers aldosterone specificity to the mineralocorticoid receptor. In vivo mineralocorticoid receptor activation by glucocorticoids depends on low 11βHSD2 activity. Moreover, glucocorticoids exert important renal hemodynamic actions; they increase renal blood flow and the glomerular filtration rate by increasing renal production of prostaglandins, nitric oxide, and dopamine.31, 32, 33 Finally, glucocorticoids upregulate the gene expression of natriuretic peptides and increase their levels in the circulation.34, 35 These data indicate a dual effect of glucocorticoids on renal tubules: direct action and indirect action secondary to hemodynamic changes. Nevertheless, the integrated response of the kidneys to the systemic administration of glucocorticoids (ie, increased glomerular filtration rate, enhanced renal diuresis, decrease serum creatinine, increased creatinine clearance, and induced natriuresis or antinatriuresis) is well established and has been demonstrated by clinical trials and our studies (Figure S4). This phenomenon is generally explained by the hemodynamic actions of glucocorticoids, which override their direct actions on renal tubules, increasing the net urinary Na+ excretion. Our experimental data indicate that the direct action of glucocorticoids on renal tubules may also play an important role in the maintenance of body water homeostasis.

We also observed that dexamethasone might increase cardiac contractility and alleviate ventricular diastolic dysfunction, leading to HF improvement. These favorable cardiac effects may partly contribute to renal hemodynamic changes, thereby improving renal function (Figure S4). Conversely, it could be a consequence of preload reduction attributed to glucocorticoid‐induced diuresis. We also found that dexamethasone treatment is associated with an inhibition on myocardial fibrosis and inflammation in HF (Figures S5 and S6), which may also play a role in cardiorenal protection.36, 37, 38 Furthermore, Nishimura et al39 reported an association between methylprednisolone treatment and an increase in cardiac output and β‐adrenergic receptor density in an animal model of HF, which suggests the existence of another mechanism.

Although in our study RU486 abolished most of the biomolecular changes induced by dexamethasone, some changes remained unaffected or were even positively affected by RU486 coadministration. First, RU486 had no impact on dexamethasone‐induced NKCC2 downregulation, probably because NKCC2‐induced sodium retention is not mediated by the classical GR.40 Second, RU486 significantly increased AVP levels, consistent with previous reports,41 probably reflecting a direct signaling effect via the progesterone receptor because RU486 is a progesterone receptor antagonist. In addition, RU486 is capable of crossing the blood–brain barrier and could cause a central hypocortisolemic state, finally leading to increased AVP production.42

NKA is a key protein of sodium excretion regulation located in the basement membrane. In the present study, there was no NKA overexpression in the CHF group, and dexamethasone did not affect NKA expression in the HF rats. One possible explanation is that NKA is relatively stable in the cell plasma membrane, and external stimulation affects its activity rather than its protein abundance.43

This study provides experimental evidence supporting the clinical application of glucocorticoids to relieve water and sodium retention. However, it has several limitations. First, the effect of glucocorticoids was only studied on acute water load, and further studies are required to investigate their long‐term effects. Second, the experiment was performed using a rat model of HF. Further research in cytology is needed to confirm our findings. Finally, we tested the renal effects of glucocorticoids in the context of acute water load–induced dilutive hyponatremia. The renal effects of glucocorticoids in other contexts, such as acute salt load, remain unclear.

In summary, glucocorticoids downregulate the expression of V2R in the inner medullary collecting duct, inhibit V2R activity, increase the ability of the kidneys to secrete water and sodium, and reverse dilutive hyponatremia in rats (Figure S7). Future studies are warranted to confirm whether glucocorticoids have the same effects on humans.

CONCLUSIONS

Glucocorticoids increase renal water sodium excretion and reverse diluted hyponatremia by inhibiting the V2R pathway in an acute water loading test in rats with chronic heart failure.

Sources of Funding

This work was supported by the National Natural Science Foundation of China (No. 81670357).

Disclosures

None.

Supporting information

Data S1 Figures S1–S7

Click here for additional data file. (551.5KB, pdf)

Acknowledgments

The authors thank Dr Cowling at the University of California San Diego for his critical suggestion, comments, and extensive editing. The authors thank Dr Yin at the First Hospital of Hebei Medical University for her technical assistance.

(J Am Heart Assoc. 2020;9:e014950 DOI: 10.1161/JAHA.119.014950.)

For Sources of Funding and Disclosures, see page 10.

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