Inhibition Of Aldosterone Secretion Research Articles

OR02-06 FGFR2 Mediates Zona Glomerulosa Morphogenesis, Aldosterone Secretion And Β-Catenin-induced Adrenal Hyperplasia

Abstract Disclosure: V. Chortis: None. K. Dulanjalee: None. N.A. Guagliardo: None. M.S. Shah: None. R. Claudio: None. P.Q. Barrett: None. K.S. Borges: None. D.L. Carlone: None. D.T. Breault: None. Fibroblast Growth Factor Receptors (FGFRs) are tyrosine kinase receptors with critical roles in organogenesis and tissue homeostasis. We have recently shown that Fgfr2 deletion in the outermost zone of the mouse adrenal cortex (zona Glomerulosa, zG) during post-natal development leads to disordered morphology. Interestingly, Fgfr2 is up-regulated in the zG of mice with adrenal hyperplasia due to constitutive activation of Wnt/beta-catenin signaling. Here, we seek to delineate the role of FGFR2 in adrenal morphology and function during postnatal development, adulthood homeostasis, as well as during β-catenin-induced adrenal hyperplasia. To address this, we used i) a mouse model of conditional Fgfr2 loss (Fgfr2-cKO), in which zG-specific Fgfr2 deletion begins during early post-natal development, and ii) an inducible mouse model (Fgfr2-icKO), in which Fgfr2 deletion in the zG during adult life is tamoxifen-dependent. Fgfr2 loss in Fgfr2-cKO mice disrupted zG cell differentiation in steroidogenically mature cells and limited their capacity to proliferate and undergo trans-differentiation into the adjacent zona Fasciculata. zG cell de-differentiation was also evident upon acute loss of Fgfr2 in adult Fgfr2-icKO mice. Furthermore, Fgfr2 loss in a mouse model of beta-catenin-induced zG hyperplasia was sufficient to fully abrogate adrenal hyperplasia. Treatment with pan-FGFR small molecule inhibitors suppressed cellular proliferation in the mouse zG and inhibited aldosterone secretion. Taken together, these results suggest FGFR2 has a critical role in normal adrenal development and tissue homeostasis and is an essential mediator of beta-catenin-induced adrenal hyperplasia. FGFR2 targeting may be meaningful in patients with conditions associated with aldosterone excess. Presentation: Thursday, June 15, 2023

Sfrp2 regulates the WNT/β-catenin pathway to slow the development of aldosterone-producing adenoma.

To explore a new drug therapy for aldosterone-producing adenoma (APA), and investigate whether Sfrp2 (secreted frizzled-related protein 2) can influence the development of adrenal APA by regulating the WNT/β-catenin pathway. Tissue samples from APA patients were collected to detect the expression of Sfrp2 and β-catenin in APA. NCI-H295R cells were cultured with WNT/β-catenin pathway inhibitors to detect cell proliferation and aldosterone secretion. Then, the expression of Sfrp2 was altered to determine the effect of Sfrp2 expression on WNT/β-catenin pathway activity and aldosterone adenocarcinoma cells. Finally, a mouse APA model was established, and the mice were intravenously injected with WNT/β-catenin pathway inhibitors or transfected with the Sfrp2 gene. The activity of the WNT/β-catenin pathway, blood pressure, aldosterone secretion, and cell growth in the mice were then observed. β-catenin was overexpressed in APA tissues, while Sfrp2 was underexpressed. Sfrp2 can negatively regulate β-catenin expression and control the activity of the WNT/β-catenin pathway. Increased Sfrp2 expression inhibited the activity of the WNT/β-catenin pathway, which suppressed aldosterone secretion and APA cell proliferation. The in vivo experiments also demonstrated that inhibition of WNT/β-catenin pathway activity in mice reduced the arterial pressure and aldosterone concentration. The increased expression of Sfrp2 can inhibit the WNT/β-catenin pathway in mice, and can also reduce arterial pressure and APA tissue growth. Sfrp2 can inhibit the WNT/β-catenin signaling pathway by suppressing the expression of β-catenin, thus controlling the concentration of aldosterone and hindering APA development. This study provides a novel therapeutic target for the treatment of APA and a new direction for future research.

Prospective evaluation of a telmisartan suppression test as a diagnostic tool for primary hyperaldosteronism in cats.

In a previous study, telmisartan suppressed aldosterone secretion in healthy cats but not in cats with primary hyperaldosteronism (PHA). Telmisartan suppresses aldosterone secretion in middle-aged healthy cat and cats with diseases that may result in secondary hyperaldosteronism, but not in those with PHA. Thirty-eight cats: 5 with PHA; 16 with chronic kidney disease (CKD), subclassified as hypertensive (CKD-H) or non-hypertensive (CKD-NH); 9 with hyperthyroidism (HTH); 2 with idiopathic systemic arterial hypertension (ISH); and 6 healthy middle-aged cats. Prospective, cross-sectional study. Serum aldosterone concentration, potassium concentration, and systolic blood pressure were measured before and 1 and 1.5 hours after PO administration of 2 mg/kg of telmisartan. The aldosterone variation rate (AVR) was calculated for each cat. No significant difference in the minimum AVR was observed among groups (median [quartile 1 (Q1); quartile 3 (Q3)]: 25 [0; 30]; 5 [-27; -75]; 10 [-6; -95]; 53 [19; 86]; 29 [5; 78]) for PHA, CKD, HTH, ISH, and healthy cats, respectively (P = .05). Basal serum aldosterone concentration (pmol/L) was significantly higher in PHA cats (median [Q1; Q3]: 2914 [2789; 4600]) than in CKD-H cats (median [Q1; Q3]: 239 [189; 577], corrected P value = .003) and CKD-NH cats (median [Q1; Q3]: 353 [136; 1371], corrected P value = .004). The oral telmisartan suppression test using a single dose of 2 mg/kg telmisartan did not discriminate cats with PHA from healthy middle-aged cats or cats with diseases that may result in secondary hyperaldosteronism.

Evaluation of oral telmisartan administration as a suppression test for diagnosis of primary hyperaldosteronism in cats.

Development of a telmisartan-based suppression test may facilitate the diagnosis of primary hyperaldosteronism (PHA) in cats, which remains difficult today. To develop a telmisartan suppression test (TST) that is safe, and able to suppress aldosterone secretion in healthy cats but not in cats with PHA. Ten healthy cats and 6 cats with PHA. Prospective study using a placebo-controlled crossover design to investigate a TST in healthy cats, and evaluation of TST in cats with PHA. Plasma aldosterone concentration, potassium concentration, and systolic blood pressure (SBP) were measured before (T0), and 1 hour (T1) and 1.5 hours after (T1.5) PO administration of 1 mg/kg of telmisartan, 2 mg/kg of telmisartan or placebo. Median age in healthy cats was 3 years old (range, 1-7). In healthy cats, a telmisartan dose of 2 mg/kg significantly decreased aldosterone concentration at T1 and T1.5 compared with T0. Placebo had no significant effect on aldosterone concentration. In cats diagnosed with PHA, a 2-mg/kg dose of telmisartan did not induce any significant change in aldosterone concentration at T1 or T1.5 compared with T0. No adverse effects of telmisartan (e.g., hyperkalemia, systemic hypotension) were observed in any cats. The oral TST shows promise as a diagnostic test for the diagnosis of PHA in cats.

PS-B04-8: YM750, AN ACAT1 INHIBITOR, REDUCES ALDOSTERONE SECRETION BY DECREASING ADRENAL CYP11B2 EXPRESSION

Primary aldosteronism (PA) is a refractory hypertension that accounts for approximately 5%-10% of hypertensive patients. aldosterone-producing adenomas and idiopathic hyperaldosteronism are known causes of PA. In aldosterone-producing adenomas, depolarization due to somatic mutations of ion channels in adrenocortical cells is considered the cause of aldosterone oversecretion. Recently, there have been reports on the expression of various cholesterol-metabolizing enzymes in aldosterone-producing adenomas, suggesting that intracellular cholesterol metabolism is very important for aldosterone secretion. We present here the possibility that an inhibitor of Acetyl-CoA acetyltransferase (ACAT1), an enzyme that converts cholesterol to cholesteryl esters, may inhibit aldosterone secretion by depolarization in adrenal cells. Potassium chloride and YM750, an ACAT1 inhibitor, were added to human adrenocortical carcinoma, H295R cells. Then, we measured aldosterone synthase gene, CYP11B2 mRNA expression level. As a result, the expression level of CYP11B2 decreased. Both NURR1 and NGFIB mRNA expression levels also decreased. Additionally, aldosterone production was also measured and found to be significantly decreased in the YM750 added group. Next, angiotensin II was added and the inhibitory effect of YM750 was examined. The results showed that CYP11B2 expression was not decreased. This indicates that YM750 decreased the induction of CYP11B2 expression in a potassium chloride-induced stimulus-specific manner. The experimental results suggest that YM750 specifically inhibits CYP11B2 gene expression by cell depolarization and suppresses aldosterone secretion. However, there are few reports of cholesterol metabolism affecting CYP11B2 gene expression. In this study, we found that intracellular cholesterol metabolism may affect CYP11B2 gene expression. We plan to investigate the relationship between ACAT inhibition and CYP11B2 gene expression in detail mechanisms in the future.

Research Progress on the Efficacy and Safety of Spironolactone in Reversing Left Ventricular Hypertrophy in Hemodialysis Patients.

The mineralocorticoid receptor antagonist spironolactone has been shown to improve cardiac function and reverse left ventricular hypertrophy in heart failure patients, but there are no consistent findings on the efficacy and safety in hemodialysis patients. Abnormal aldosterone secretion plays a critical role in the formation of left ventricular hypertrophy. Because of the existence of "aldosterone escape", the routine use of angiotensin-converting enzyme inhibitors/angiotensin receptor blockers does not completely inhibit aldosterone secretion. Low-dose spironolactone (25 mg/d) has been found in small-sample clinical studies to have a significant positive impact with respect to decreasing left ventricular mass index, increasing left ventricular ejection fraction, reversing left ventricular hypertrophy, and improving cardiovascular function while still being safe. More prospective multicenter clinical trials with large sample sizes are needed, however, to provide convincing evidence.

YM750, an ACAT Inhibitor, Acts on Adrenocortical Cells to Inhibit Aldosterone Secretion Due to Depolarization.

Primary aldosteronism (PA) is considered the most common form of secondary hypertension, which is associated with excessive aldosterone secretion in the adrenal cortex. The cause of excessive aldosterone secretion is the induction of aldosterone synthase gene (CYP11B2) expression by depolarization of adrenocortical cells. In this study, we found that YM750, an Acyl-coenzyme A: cholesterol acyltransferase (ACAT) inhibitor, acts on adrenocortical cells to suppress CYP11B2 gene expression and aldosterone secretion. YM750 inhibited the induction of CYP11B2 gene expression by KCl stimulation, but not by angiotensin II and forskolin stimulation. Interestingly, YM750 did not inhibit KCl-stimulated depolarization via an increase in intracellular calcium ion concentration. Moreover, ACAT1 expression was relatively abundant in the zona glomerulosa (ZG) including these CYP11B2-positive cells. Thus, YM750 suppresses CYP11B2 gene expression by suppressing intracellular signaling activated by depolarization. In addition, ACAT1 was suggested to play an important role in steroidogenesis in the ZG. YM750 suppresses CYP11B2 gene expression and aldosterone secretion in the adrenal cortex, suggesting that it may be a potential therapeutic agent for PA.

BIOCHEMICAL, HISTOPATHOLOGICAL, AND GENETIC CHARACTERIZATION OF POSTURE RESPONSIVE AND UNRESPONSIVE ALDOSTERONE-PRODUCING ADENOMAS

Objective: Aldosterone-producing adenoma (APA) accounts for ∼30% of primary aldosteronism. Based on responses of aldosterone to upright posture, APA can be divided into posture-responsive and –unresponsive forms. Somatic gene mutations in KCNJ5, CACNA1D, ATP1A1, or ATP2B3 have been reported to exist in more than 90% of APAs. We sought to compare the biochemical, histopathological, and genetic characterization between these two types of APAs. Design and method: Posture-responsive was defined as showing a rise in plasma aldosterone concentration of at least 50% 2 - 3 h after the assumption of upright posture (10 AM) above the basal level (7 AM) following overnight recumbency. Plasma levels of aldosterone and hybrid steroids (18-oxocortisol and 18-hydroxycortisol) were measured by LC-MS/MS. Histologic analysis and immunohistochemistry for CYP11B2 (aldosterone synthase) and CYP17A1 (17aplha-hydroxylase) were performed on APA tissue sections collected from 24 posture-unresponsive and 17 posture-responsive APA patients. Sanger sequencing of KCNJ5 and gene targeted next-generation sequencing were performed to detect somatic gene mutations. Results: Compared to patients with posture-responsive APA (of which 48.7% were composed of zona glomerulosa (ZG)-like cells and 35.3% showed ZG-zona fasciculata (ZF) mixed appearance), posture-unresponsive APA patients displayed higher (P < 0.01) levels of hybrid steroids, recumbent aldosterone and cortisol, greater (P < 0.05) suppression of aldosterone secretion from the contralateral unaffected adrenal, and larger (P < 0.01) tumors mostly composed of ZF-like cells that had higher (P < 0.01) expression of CYP17A1 (but not of CYP11B2). Of 41 studied APAs, 37 (90.2%) harboured aldosterone-driving somatic mutations (KCNJ5 = 14, 34.1%; CACNA1D = 13, 31.7%; ATP1A1 = 8, 19.5%; and ATP2B3 = 2, 4.9%), including 5 that were previously unreported (3 in CACNA1D and 2 in ATP1A1). Interestingly, 64.7% (11/17) of posture-responsive APAs carried CACNA1D mutations, whereas 54.2% (13/24) of posture-unresponsive APAs harboured KCNJ5 mutations. Conclusions: The excessive production of hybrid steroids by posture-unresponsive APAs may relate to their ZF-like tumor cell composition, resulting in strong expression of CYP17A1 (in addition to somatic gene mutation-driven CYP11B2 expression), thereby allowing production of cortisol which acts as the substrate for CYP11B2-generated hybrid steroids.

Proline-glucose Amadori compounds: Aqueous preparation, characterization and saltiness enhancement

Amadori rearrangement product (ARP) derived from proline and glucose was prepared in aqueous medium, and purified by ion exchange chromatography and identified by mass spectrometry and nuclear magnetic resonance spectrometry. The ARP was confirmed as 1-deoxy-1-L-proline-D-fructose (C11H19O7N, 277 Da) with four main isomers. A preliminary vacuum dehydration coupled with subsequent spray drying was used to improve the yield of ARP conversion from 3.63% to 69.15%. Furthermore, the taste characteristics of spray dried ARP products were analyzed by electronic tongue and sensory evaluation. The results indicated that when the dosage of ARP products was above 0.4%, a 20% salt reduction could be achieved without reduction in the salty taste as well as having a significant enhancement in the umami attribute. The products at low- and medium- extents of reaction could stimulate more secretion of aldosterone in oral cavity and then improve its sensitivity to the salt, while the product at high- extent of reaction inhibits aldosterone secretion.

Soy isoflavone-caused shunting of the corticosteroidogenesis pathways in andropausal subjects: Top-down impulse for the optimal supplementation design

In a series of our previous works, we revealed the beneficial effects of applied soy isoflavones (genistein or daidzein) on the wide context of corticosteroidogenesis in vivo, in a rat model of the andropause. Soy isoflavones decreased the circulating levels of pituitary adrenocorticotropic hormone, inhibited aldosterone secretion, as well as corticosterone production and secretion, but stimulated dehydroepiandrosterone secretion, all in andropausal rats. In vitro studies indicate that the mechanism underlying these hormonal changes relies on inhibition of the pituitary tyrosine kinase and adrenocortical 3β-hydroxysteroid dehydrogenase enzymes by soy isoflavones. Although the clinical studies are in their infancy, the opinion is that genistein and daidzein have therapeutic potential for the safe treatment of ageing-caused androgen deprivation and glucocorticoid excess with related metabolic/hemodynamic issues in males. Our accumulated experience and knowledge in the field of biomedical effects of plant polyphenols have provided a platform for potential recommending the agenda to organize and accelerate experimental research aimed at producing the optimal supplementation. We hypothesize that an in vivo approach should first be exploited in the sequence of investigative steps, followed by in vitro studies and synchronously conducted molecular docking analyses. In vivo research, besides establishing the margin of exposure safety or adjustment of the correct polyphenol dose, enables identification and quantification of the metabolites of applied polyphenols in the blood. Subsequent in vitro exploitation of the metabolites and related docking analyses provide clarification of the molecular mechanisms of action of applied polyphenols. Chemical modification of the polyphenol structure or coupling it with nanoparticles might be the next step in optimizing the design of supplementation. Selected, intact or chemically-modified polyphenol molecules should be included in preclinical studies on a more closely-related species, while clinical studies would finally assess the safety and effectiveness of a polyphenol-based remedial strategy. The final supplement represents a product of an appropriate technological process, conducted in accordance with the recommendations derived from the preceding research.

Aliskiren Reduces the Adrenal Zona Glomerulosa Apoptosis and Autophagy in Wistar Rats with 2K1C Hypertension.

Hypertension is a disease classified as primary or secondary, manifested not only by elevation of blood pressure but also involved in structural and functional changes of target organs. Renal artery stenosis is a leading factor of secondary hypertension, and its progress is associated with overactivation of the renin-angiotensin-aldosterone system (RAAS). Aliskiren is a renin inhibiting drug that suppresses RAAS and culminates in decreased renin release, plasma angiotensin II concentration, and inhibition of aldosterone secretion. In this sense, the aim of the present study was to analyze the structural and ultrastructural morphophysiology of the adrenal glomerular zone, after treatment with aliskiren in Wistar rats with 2K1C hypertension. Parameters as structure and ultrastructure of the adrenal glomerular zone, cellular apoptosis, nuclear cell proliferation, and AT1 receptor expression were analyzed by immunostaining and electron microscopy. Our results showed that the hypertensive animals treated with aliskiren presented a reestablishment of AT1 receptor expression and decrease in apoptosis and autophagy. In addition, treatment with aliskiren improves the cell aspects in the adrenal glomerular zone, evidenced by ultrastructural analysis through preserved nuclei and well-developed mitochondria. Therefore, our evidence suggests that aliskiren has a beneficial effect on the adrenal glomerular zone remodeling in animals with renovascular hypertension.

The Effects of Different Calcium Channel Blockers on Aldosterone-Producing Adenoma Cells.

Purpose: The aim of this study is to examine the effects of different kinds of calcium channel blockers (CCBs) on primary aldosterone-producing adenoma (APA) mainly with KCNJ5 mutations. Primary cultured APA cells were treated with different calcium channel blockers (L/T type CCB benidipine, T-type CCB mibefradil and L-type CCB nifedipine), and aldosterone secretagogues with or without nifedipine. Aldosterone level, aldosterone synthase (CYP11B2) mRNA expression and cell proliferation were detected. The results showed that all three CCBs significantly inhibit aldosterone secretion and CYP11B2 mRNA expression. Benidipine was relatively more effective than mibefradil or nifedipine. In addition, only mibefradil marginally inhibited cell proliferation. Adrenocorticotropin (ACTH) had a much stronger effect in stimulating aldosterone secretion and promoting cell proliferation from APA's than angiotensin II (ATII). Different from ACTH and ATII, potassium had no effect. Nifedipine inhibited the basal and ACTH-, ATII-elicited aldosterone secretion. Twenty three of 24 APAs had somatic KCNJ5 mutation. In conclusion, benidipine, mibefradil and nifedipine significantly inhibit aldosterone secretion in primary cultured APA cells.

L- and T-type calcium channels control aldosterone production from human adrenals.

Aldosterone, which plays a key role in the regulation of blood pressure, is produced by zona glomerulosa (ZG) cells of the adrenal cortex. Exaggerated overproduction of aldosterone from ZG cells causes primary hyperaldosteronism. In ZG cells, calcium entry through voltage-gated calcium channels plays a central role in the regulation of aldosterone secretion. Previous studies in animal adrenals and human adrenal adrenocortical cell lines suggest that the T-type but not the L-type calcium channel activity drives aldosterone production. However, recent clinical studies show that somatic mutations in L-type calcium channels are the second most prevalent cause of aldosterone-producing adenoma. Our objective was to define the roles of T and L-type calcium channels in regulating aldosterone secretion from human adrenals. We find that human adrenal ZG cells mainly express T-type CaV3.2/3.3 and L-type CaV1.2/1.3 calcium channels. TTA-P2, a specific inhibitor of T-type calcium channel subtypes, reduced basal aldosterone secretion from acutely prepared slices of human adrenals. Surprisingly, nifedipine, the prototypic inhibitor of L-type calcium channels, also decreased basal aldosterone secretion, suggesting that L-type calcium channels are active under basal conditions. In addition, TTA-P2 or nifedipine also inhibited aldosterone secretion stimulated by angiotensin II- or elevations in extracellular K+. Remarkably, blockade of either L- or T-type calcium channels inhibits basal and stimulated aldosterone production to a similar extent. Low concentrations of TTA-P2 and nifedipine showed additive inhibitory effect on aldosterone secretion. We conclude that T- and L-type calcium channels play equally important roles in controlling aldosterone production from human adrenals.

Liddle's syndrome mechanisms, diagnosis and management.

Liddle’s syndrome is a genetic disorder characterized by hypertension with hypokalemic metabolic alkalosis, hyporeninemia and suppressed aldosterone secretion that often appears early in life. It results from inappropriately elevated sodium reabsorption in the distal nephron. Liddle’s syndrome is caused by mutations to subunits of the Epithelial Sodium Channel (ENaC). Among other mechanisms, such mutations typically prevent ubiquitination of these subunits, slowing the rate at which they are internalized from the membrane, resulting in an elevation of channel activity. A minority of Liddle’s syndrome mutations, though, result in a complementary effect that also elevates activity by increasing the probability that ENaC channels within the membrane are open. Potassium-sparing diuretics such as amiloride and triamterene reduce ENaC activity, and in combination with a reduced sodium diet can restore normotension and electrolyte imbalance in Liddle’s syndrome patients and animal models. Liddle’s syndrome can be diagnosed clinically by phenotype and confirmed through genetic testing. This review examines the clinical features of Liddle’s syndrome, the differential diagnosis of Liddle’s syndrome and differentiation from other genetic diseases with similar phenotype, and what is currently known about the population-level prevalence of Liddle’s syndrome. This review gives special focus to the molecular mechanisms of Liddle’s syndrome.

GSTA1 Expression Is Correlated With Aldosterone Level in KCNJ5-Mutated Adrenal Aldosterone-Producing Adenoma.

KCNJ5 mutation is a major cause of aldosterone-producing adenomas (APAs). The development of APA apart from KCNJ5 mutation is less investigated. To investigate other mechanisms affecting aldosterone secretion apart from KCNJ5. Six pairs of KCNJ5-mutated, high and low aldosterone-secreting APAs, five non-KCNJ5-mutated APAs, and four normal adrenal glands were assayed by Affymetrix GeneChip Human Transcriptome Array 2.0. A total of 113 APA samples were investigated to explore the expression of glutathione-S-transferase A1 (GSTA1). H295R cells were used to verify the function of GSTA1. GSTA1 was the top gene downregulated in high-aldosterone KCNJ5-mutated APAs. GSTA1 was also downregulated in KCNJ5-mutated APAs compared with wild-type KCNJ5 APAs. Accordingly, mutant KCNJ5 decreased GSTA1 messenger RNA and protein expression levels. GSTA1 overexpression suppressed aldosterone secretion whether in wild-type or mutant KCNJ5 H295R cells. Adding ethacrynic acid or silencing of GSTA1 increased aldosterone secretion by increasing reactive oxygen species (ROS), superoxide, H2O2 levels, and Ca2+ influx. The expression of the transcription factors NR4A1, NR4A2, and CAMK1 and intracellular Ca2+ were significantly upregulated by GSTA1 inhibition. The reduced form of NAD phosphate oxidase inhibitor or H2O2 scavenger or blocking calmodulin or calcium channels could significantly reduce aldosterone secretion in GSTA1-inhibited cells. (1) GSTA1 expression is reversely correlated with aldosterone level in KCNJ5-mutated APAs, (2) GSTA1 regulates aldosterone secretion by ROS and Ca2+ signaling, and (3) KCNJ5 mutation downregulates GSTA1 expression, and overexpression of GSTA1 reverses increased aldosterone in KCNJ5-mutated adrenal cells.

Potassium Sensing by Renal Distal Tubules Requires Kir4.1.

The mammalian distal convoluted tubule (DCT) makes an important contribution to potassium homeostasis by modulating NaCl transport. The thiazide-sensitive Na+/Cl- cotransporter (NCC) is activated by low potassium intake and by hypokalemia. Coupled with suppression of aldosterone secretion, activation of NCC helps to retain potassium by increasing electroneutral NaCl reabsorption, therefore reducing Na+/K+ exchange. Yet the mechanisms by which DCT cells sense plasma potassium concentration and transmit the information to the apical membrane are not clear. Here, we tested the hypothesis that the potassium channel Kir4.1 is the potassium sensor of DCT cells. We generated mice in which Kir4.1 could be deleted in the kidney after the mice are fully developed. Deletion of Kir4.1 in these mice led to moderate salt wasting, low BP, and profound potassium wasting. Basolateral membranes of DCT cells were depolarized, nearly devoid of conductive potassium transport, and unresponsive to plasma potassium concentration. Although renal WNK4 abundance increased after Kir4.1 deletion, NCC abundance and function decreased, suggesting that membrane depolarization uncouples WNK kinases from NCC. Together, these results indicate that Kir4.1 mediates potassium sensing by DCT cells and couples this signal to apical transport processes.

Bucindolol Prevents Atrial Flutter via the Beta-1 389 Arg/Gly Adrenergic Receptor Polymorphism

Background: Loop diuretics are the mainstay of treatment for volume overload in heart failure. Data is limited as to which loop diuretic is the preferred agent. Studies in animal models suggest that torsemide may have a positive anti-aldosterone effect, through receptor antagonism and inhibition of aldosterone secretion. However, the clinical significance of these effects in human heart failure is unknown. Hypothesis: If the anti-aldosterone effects of torsemide are clinically meaningful, potassium losses from torsemide should be reduced compared to other loop diuretics lacking anti-aldosterone effects. Methods: We studied 75 hospitalized heart failure patients treated with loop diuretics. Within this sample, 51 patients received bumetanide, 25 torsemide, and 12 furosemide with 13 patients receiving both bumetanide and torsemide on different days. A spot urine was collected prior to diuretic administration and then a timed 6-hour urine collection was performed after diuretic administration to determine total potassium excretion. Values reported represent median (quartile 1 quartile 4). Results: The doses of bumetanide, torsemide, and furosemide received were 3 mg (2-4 mg), 40 mg (20-70 mg) and 40 mg (25-80 mg), respectively. There was no significant difference in total potassium excretion and the potassium to sodium excretion ratio between the patients on torsemide, bumetanide and furosemide (Table 1). There was also no significant difference in fractional excretion of potassium (FEK) or change in FEK between patients on different diuretics (Table 1). In the subgroup of patients that received both bumetanide and torsemide on different days (n513) total potassium excretion (p50.30), potassium to sodium excretion ratio (p50.58), FEK (p50.41), and change in FEK (p50.74) were similar across diuretics. Conclusion: Torsemide did not produce a detectable change in total potassium excretion or potassium handling compared to furosemide or bumetanide. Acute anti-aldosterone effects of torsemide do not appear to be clinically significant in heart failure patients receiving high dose loop diuretics.

The Anti-aldosterone Effects of Torsemide Do Not Lead to Detectable Improvement in Potassium Losses in Patients Treated for Decompensated Heart Failure

Background: Loop diuretics are the mainstay of treatment for volume overload in heart failure. Data is limited as to which loop diuretic is the preferred agent. Studies in animal models suggest that torsemide may have a positive anti-aldosterone effect, through receptor antagonism and inhibition of aldosterone secretion. However, the clinical significance of these effects in human heart failure is unknown. Hypothesis: If the anti-aldosterone effects of torsemide are clinically meaningful, potassium losses from torsemide should be reduced compared to other loop diuretics lacking anti-aldosterone effects. Methods: We studied 75 hospitalized heart failure patients treated with loop diuretics. Within this sample, 51 patients received bumetanide, 25 torsemide, and 12 furosemide with 13 patients receiving both bumetanide and torsemide on different days. A spot urine was collected prior to diuretic administration and then a timed 6-hour urine collection was performed after diuretic administration to determine total potassium excretion. Values reported represent median (quartile 1 quartile 4). Results: The doses of bumetanide, torsemide, and furosemide received were 3 mg (2-4 mg), 40 mg (20-70 mg) and 40 mg (25-80 mg), respectively. There was no significant difference in total potassium excretion and the potassium to sodium excretion ratio between the patients on torsemide, bumetanide and furosemide (Table 1). There was also no significant difference in fractional excretion of potassium (FEK) or change in FEK between patients on different diuretics (Table 1). In the subgroup of patients that received both bumetanide and torsemide on different days (n513) total potassium excretion (p50.30), potassium to sodium excretion ratio (p50.58), FEK (p50.41), and change in FEK (p50.74) were similar across diuretics. Conclusion: Torsemide did not produce a detectable change in total potassium excretion or potassium handling compared to furosemide or bumetanide. Acute anti-aldosterone effects of torsemide do not appear to be clinically significant in heart failure patients receiving high dose loop diuretics.

Potassium Modulates Electrolyte Balance and Blood Pressure through Effects on Distal Cell Voltage and Chloride

Dietary potassium deficiency, common in modern diets, raises blood pressure and enhances salt sensitivity. Potassium homeostasis requires a molecular switch in the distal convoluted tubule (DCT), which fails in familial hyperkalemic hypertension (pseudohypoaldosteronism type 2), activating the thiazide-sensitive NaCl cotransporter, NCC. Here, we show that dietary potassium deficiency activates NCC, even in the setting of high salt intake, thereby causing sodium retention and a rise in blood pressure. The effect is dependent on plasma potassium, which modulates DCT cell membrane voltage and, in turn, intracellular chloride. Low intracellular chloride stimulates WNK kinases to activate NCC, limiting potassium losses, even at the expense of increased blood pressure. These data show that DCT cells, like adrenal cells, sense potassium via membrane voltage. In the DCT, hyperpolarization activates NCC via WNK kinases, whereas in the adrenal gland, it inhibits aldosterone secretion. These effects work in concert to maintain potassium homeostasis.

Case Report: Hyponatremia of malignancy – An alternative mechanism? Syndrome of inappropriate atrial natriuretic peptide (SIANP)

Euvolemic hyponatremia in the setting of lung cancer is most commonly due to the syndrome of inappropriate anti-diuretic hormone secretion (SIADH). However, a subset of patients with small cell carcinoma and hyponatremia also have elevated levels of atrial natriuretic peptide (ANP), which is produced by some small cell tumors. We report the case of a 64-year-old man with a limited-stage small cell carcinoma of the lung undergoing chemoradiation therapy, who was admitted to hospital with a pulmonary embolism. Two months earlier, at the time of diagnosis with lung cancer, he had a hypotonic, euvolemic hyponatremia, presumed to be caused by SIADH. At that time, his serum sodium readily normalized with fluid restriction and ADH-antagonist therapy with demeclocycline. However, during his second admission, the hyponatremia was refractory to treatment: his sodium level slowly declined from 138 mmol/L to a nadir of 118 mmol/L, despite early initiation of fluid restriction and maximal doses of demeclocycline. Laboratory values revealed a low but inappropriately non-zero level of ADH but also an inappropriately low level of aldosterone and an elevated level of ANP, suggesting that SIADH might not be the only contributor to the hyponatremia. While a causal link between ectopic ANP production and hyponatremia has never been established, an inappropriately high level of ANP can directly decrease sodium re-absorption in the proximal convoluted tubule of the kidney and increase glomerular filtration rate (GFR), resulting in greater excretion of sodium and water. In addition, high circulating levels of ANP can inhibit aldosterone secretion, potentially resulting in further sodium wasting. Here, the elevated ANP and inappropriately low aldosterone suggested the possibility that the refractory hyponatremia, although initiated by SIADH, was further worsened by an ANP-mediated natriuresis and suppression of aldosterone response.