Specific Mineralocorticoid Receptor Antagonist Research Articles

Effect of Mineralocorticoid receptor antagonism (MRA) on aldosterone-interleukin 6 axis in heart failure; second opinion. A case-control study

BackgroundIn cases of heart failure characterized by reduced ejection fraction (HFrEF), heightened levels of aldosterone negatively impact the progression of heart failure. Aldosterone exerts its influence through the activation of mineralocorticoid receptors, leading to the subsequent release of IL-6. Recently, the discovery of the role of mineralocorticoid receptor antagonism (MRA) in managing the progression of heart failure, particularly through its effect on IL-6, prompted its inclusion in the American College of Cardiology guidelines. In the years 2019 and 2021, studies elucidated the proinflammatory role of interleukin 6 in the cytokine storm associated with COVID-19, emphasizing the significance of IL-6 inhibitors in controlling this storm. Further research is required to examine the impact of mineralocorticoid receptor antagonism (MRA) on both aldosterone levels and IL-6 release in patients with HFrEF. Additionally, there is a need to assess the effectiveness of current MRA dosages in controlling heart failure with reduced ejection fraction.Patients and methodsA retrospective analysis was conducted on 108 patients with HFrEF diagnosed through echocardiography. The study covered the period from December 2021 to December 2022. All participants underwent blood tests for aldosterone and interleukin 6 using the ELISA test. The patients were categorized based on cardiac compensation status and the specific mineralocorticoid receptor antagonist (MRA) drug regimen they were on.ResultsThere was a notable rise in aldosterone levels and a reduction in serum IL6 observed in 30 patients with Acute Decompensated Heart Failure (ADHF) who were treated with Mineralocorticoid Receptor Antagonists (MRA), as compared to 30 patients with a similar diagnosis who did not receive MRA. Among 24 patients with compensated heart failure using MRA, there was a significant increase in aldosterone levels and a decrease in IL6, in contrast to 24 patients with compensated heart failure who were not on MRA therapy.ConclusionsIn heart failure with reduced ejection fraction (HFrEF), inhibiting mineralocorticoid receptors leads to a reduction in pro-inflammatory IL-6. The action of Mineralocorticoid Receptor Antagonists (MRA) is deemed safe, well-tolerated, and cost-effective when compared to IL-6 inhibitors. There is a need to reevaluate the current MRA regimen with the objective of enhancing its efficacy for optimal reduction in IL-6 and effective control of heart failure progression.

Role of Aldosterone and Mineralocorticoid Receptor in Cardiovascular Aging.

The mineralocorticoid receptor (MR) was originally identified as a regulator of blood pressure, able to modulate renal sodium handling in response to its principal ligand aldosterone. MR is expressed in several extra-renal tissues, including the heart, vasculature, and adipose tissue. More recent studies have shown that extra-renal MR plays a relevant role in the control of cardiovascular and metabolic functions and has recently been implicated in the pathophysiology of aging. MR activation promotes vasoconstriction and acts as a potent pro-fibrotic agent in cardiovascular remodeling. Aging is associated with increased arterial stiffness and vascular tone, and modifications of arterial structure and function are responsible for these alterations. MR activation contributes to increase blood pressure with aging by regulating myogenic tone, vasoconstriction, and vascular oxidative stress. Importantly, aging represents an important contributor to the increased prevalence of cardiometabolic syndrome. In the elderly, dysregulation of MR signaling is associated with hypertension, obesity, and diabetes, representing an important cause of increased cardiovascular risk. Clinical use of MR antagonists is limited by the adverse effects induced by MR blockade in the kidney, raising the risk of hyperkalaemia in older patients with reduced renal function. Therefore, there is an unmet need for the enhanced understanding of the role of MR in aging and for development of novel specific MR antagonists in the context of cardiovascular rehabilitation in the elderly, in order to reduce relevant side effects.

Spironolactone Depletes the XPB Protein and Inhibits DNA Damage Responses in UVB-Irradiated Human Skin

UVB wavelengths of light induce the formation of photoproducts in genomic DNA that are potentially mutagenic and detrimental to epidermal cell function. The mineralocorticoid and androgen receptor antagonist spironolactone (SP) was recently identified as an inhibitor of UV photoproduct removal in human cancer cells invitro via its ability to promote the rapid proteolytic degradation of the DNA repair protein XPB. Using normal human keratinocytes invitro and skin explants exvivo, we found that SP rapidly depleted XPB protein in both systems and abrogated two major responses to UVB-induced DNA damage, including the removal of UV photoproducts from genomic DNA and the activation of ATR/ATM DNA damage kinase signaling. These effects were also correlated with both mutagenesis and a predisposition to UVB-induced cell death but were unique to SP, because neither the SP metabolites canrenone and 7α-thiomethylspironolactone nor the more specific mineralocorticoid receptor antagonist eplerenone affected XPB protein levels or the UVB response. Our findings provide an approach for studying XPB and its roles in the UVB DNA damage response in human skin exvivo and indicate that SP may increase UVB mutagenesis and skin cancer risk in certain individuals.

Similar efficacy from specific and non-specific mineralocorticoid receptor antagonist treatment of muscular dystrophy mice.

Combined treatment with an angiotensin-converting enzyme inhibitor and a mineralocorticoid receptor (MR) antagonist improved cardiac and skeletal muscle function and pathology in a mouse model of Duchenne muscular dystrophy. MR is present in limb and respiratory skeletal muscles and functions as a steroid hormone receptor. The goals of the current study were to compare the efficacy of the specific MR antagonist eplerenone with the non-specific MR antagonist spironolactone, both in combination with the angiotensin-converting enzyme inhibitor lisinopril. Three groups of n=18 dystrophin-deficient, utrophin-haploinsufficient male mice were given chow containing: lisinopril plus spironolactone, lisinopril plus eplerenone, or no drug, from four to 20 weeks-of-age. Eighteen C57BL/10 male mice were used as wild-type controls. In vivo measurements included cardiac magnetic resonance imaging, conscious electrocardiography, and grip strength. From each mouse in the study, diaphragm, extensor digitorum longus, and cardiac papillary muscle force was measured ex vivo, followed by histological quantification of muscle damage in heart, diaphragm, quadriceps, and abdominal muscles. MR protein levels were also verified in treated muscles. Treatment with specific and non-specific MR antagonists did not result in any adverse effects to dystrophic skeletal muscles or heart. Both treatments resulted in similar functional and pathological improvements across a wide array of parameters. MR protein levels were not reduced by treatment. These data suggest that spironolactone and eplerenone show similar effects in dystrophic mice and support the clinical development of MR antagonists for treating skeletal muscles in Duchenne muscular dystrophy.

A novel actor in skin biology: the mineralocorticoid receptor.

A novel actor in skin biology: the mineralocorticoid receptor.

Beneficial effects of mineralocorticoid receptor blockade in experimental non-alcoholic steatohepatitis.

Therapeutic options to treat Non-alcoholic steatohepatitis (NASH) are limited. Mineralocorticoid receptor (MR) activation could play a role in hepatic fibrogenesis and its modulation could be beneficial for NASH. To investigate whether eplerenone, a specific MR antagonist, ameliorates liver damage in experimental NASH. C57bl6 mice were fed a choline-deficient and amino acid-defined (CDAA) diet for 22 weeks with or without eplerenone supplementation. Serum levels of aminotransferases and aldosterone were measured and hepatic steatosis, inflammation and fibrosis scored histologically. Hepatic triglyceride content (HTC) and hepatic mRNA levels of pro-inflammatory pro-fibrotic, oxidative stress-associated genes and of MR were also assessed. CDAA diet effectively induced fibrotic NASH, and increased the hepatic expression of pro-inflammatory, pro-fibrotic and oxidative stress-associated genes. Hepatic MR mRNA levels significantly correlated with the expression of pro-inflammatory and pro-fibrotic genes and were significantly increased in hepatic stellate cells obtained from CDAA-fed animals. Eplerenone administration was associated to a reduction in histological steatosis and attenuation of liver fibrosis development, which was associated to a significant decrease in the expression of collagen-α1, collagen type III, alpha 1 and Matrix metalloproteinase-2. The expression of MR correlates with inflammation and fibrosis development in experimental NASH. Specific MR blockade with eplerenone has hepatic anti-steatotic and anti-fibrotic effects. These data identify eplerenone as a potential novel therapy for NASH. Considering its safety and FDA-approved status, human studies are warranted.

Mineralocorticoid receptor and cardiac arrhythmia

Mineralocorticoid receptor (MR) activation has been shown to play a deleterious role in the development of heart disease in studies using specific MR antagonists (spironolactone, eplerenone) in both experimental models and patients. Pharmacological MR blockade attenuates the transition to heart failure (HF) in models of systolic left ventricular dysfunction and myocardial infarction, as well as diastolic dysfunction, in rats and mice. In humans, MR antagonism is highly beneficial in patients with mild or advanced HF and postinfarct HF. The consequences of aldosterone and MR activation for cardiac arrhythmia and its prevention and/or correction by MR antagonists are often underestimated. Activation of MR modulates cardiac electrical activity, causing atrial and ventricular arrhythmias. A pro-arrhythmogenic effect of aldosterone (possibly partly dependent on fibrosis) has been suggested by several studies. Cardiac MR activation has important consequences for the control of cellular calcium homeostasis, action potential lengthening, modulation of calcium transients and sarcoplasmic reticulum diastolic leaks, resulting in the promotion of rhythm disorders. Aldosterone and/or MR activation (in both cardiomyocytes and coronary vessels) result in vascular dysfunction and also contribute to pro-arrhythmogenic conditions. Together, the pro-arrhythmic effects of aldosterone and/or MR may explain the highly beneficial effect of MR antagonism, namely a decrease in the incidence of sudden death, observed in the Randomized Aldactone Evaluation Study (RALES) and Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS) studies.

Mineralocorticoid receptor is involved in rat and human ocular chorioretinopathy

Central serous chorioretinopathy (CSCR) is a vision-threatening eye disease with no validated treatment and unknown pathogeny. In CSCR, dilation and leakage of choroid vessels underneath the retina cause subretinal fluid accumulation and retinal detachment. Because glucocorticoids induce and aggravate CSCR and are known to bind to the mineralocorticoid receptor (MR), CSCR may be related to inappropriate MR activation. Our aim was to assess the effect of MR activation on rat choroidal vasculature and translate the results to CSCR patients. Intravitreous injection of the glucocorticoid corticosterone in rat eyes induced choroidal enlargement. Aldosterone, a specific MR activator, elicited the same effect, producing choroid vessel dilation -and leakage. We identified an underlying mechanism of this effect: aldosterone upregulated the endothelial vasodilatory K channel KCa2.3. Its blockade prevented aldosterone-induced thickening. To translate these findings, we treated 2 patients with chronic nonresolved CSCR with oral eplerenone, a specific MR antagonist, for 5 weeks, and observed impressive and rapid resolution of retinal detachment and choroidal vasodilation as well as improved visual acuity. The benefit was maintained 5 months after eplerenone withdrawal. Our results identify MR signaling as a pathway controlling choroidal vascular bed relaxation and provide a pathogenic link with human CSCR, which suggests that blockade of MR could be used therapeutically to reverse choroid vasculopathy.

Brief neck restraint stress enhances long-term potentiation and suppresses long-term depression in the dentate gyrus of the mouse

We studied the effects of brief (10min) neck restraint on long-term potentiation (LTP) and long-term depression (LTD) in mouse dentate gyrus (DG) slices. Brain slices were prepared immediately after neck restraint and LTP/LTD induction was attempted 3.5h later. LTP enhancement and LTD suppression was observed in slices prepared from stressed animals. The corticosterone plasma concentration was elevated approx. fourfold just after the neck restraint session. To examine the role of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation in mediating the effects of neck restraint on LTP and LTD, the animals were pretreated with either the specific GR antagonist RU38486, the specific MR antagonist spironolactone, the corticosterone synthesis inhibitor metyrapone, or vehicle Tween 80. Injection with Tween 80 and subsequent neck restraint did not influence LTP enhancement or LTD suppression, but the effects of neck restraint were prevented by RU38486, spironolactone and metyrapone pretreatment. These data indicate that acute stress caused by brief neck restraint enhances LTP and impairs LTD in the dentate gyrus and that these effects are mediated by activation of GRs and MRs.

Primary aldosteronism, diagnosis and treatment in Japan

Primary aldosteronism (PA) has been recognized as a common cause of secondary hypertension and accounts for approximately 5-15% of the hypertensive population in Japan. Screening for PA should therefore be carried out in all hypertensive patients as we have shown the estimated prevalence of PA is 13.6% in pre-hypertensive subjects and 9.1% in stage 1 hypertensive patients. The screening test most advocated is the aldosterone-to-renin ratio (ARR), and when the ARR is >20 the following confirmatory tests should be carried out; the captopril challenge test, frusemide-upright test, or saline infusion test. Adrenal CT is not accurate for distinguishing between an aldosterone-producing adenoma (APA) and idiopathic hyperaldosteronism (IHA). Adrenal venous sampling (AVS) is therefore essential for selecting the appropriate therapy in patients a high probability of PA who require surgical treatment. Rapid cortisol assays during AVS to monitor cortisol levels can reduce the failure associated with AVS. We have developed a new rapid cortisol assay using immunochromatography, in which cortisol concentration can be measured within 6min. Using this technique, the success rate of AVS improved to 93%. IHA underlies about one-half of cases with PA; treatment with eplerenone (100mg twice a daily), a specific mineralocorticoid receptor antagonist, results in substantial improvement in hypertension, with fewer side effects compared to spironolactone.

Eplerenone Prevents Cerebral Vessel Remodeling in Male Hypertensive Rats

Aldosterone, a mineralocorticoid, promotes deleterious remodeling of the cardiovascular system. Spironolactone, a non-specific mineralocorticoid receptor (MR) antagonist, prevents remodeling of the middle cerebral artery (MCA) in male spontaneously hypertensive stroke-prone rats (SHRSP). We hypothesized that eplerenone (EPL), a specific MR antagonist, would also prevent remodeling of the MCA of male SHRSP. Six week old male SHRSP were treated with EPL (100 mg/kg/day) for 6 weeks. MCA structure was analyzed using a pressurized arteriograph under passive (calcium-free) conditions from 0 to 180 mmHg. Blood pressure (BP) was measured using telemetry or tail-cuff plethysmography. Lumen and outer diameters were increased (Table) and wall/lumen ratios were decreased (p<0.05, ANOVA) compared to untreated SHRSP; wall area was unchanged (p>0.05, ANOVA), indicating that EPL treatment prevented MCA remodeling. BP was not different between groups (Table), indicating a BP independent effect. In conclusion, the data indicate that effects seen previously with spironolactone are MR specific and highlight the involvement of MR activation in cerebral vessel remodeling.

MDM2: A Novel Mineralocorticoid-Responsive Gene Involved in Aldosterone-Induced Human Vascular Structural Remodeling

Aldosterone has been demonstrated to play an important role in the pathogenesis of various cardiovascular diseases. Vascular structural remodeling, including vascular smooth muscle cell (VSMC) proliferation, has been also reported in small resistance arteries of patients with primary aldosteronism. Therefore, in this study, we examined whether genes involved in the regulation of the cell cycle were induced by aldosterone alone in cultured human VSMCs and in human small resistance arteries. Results of these studies eventually demonstrated that MDM2, one of the genes involved in anti-apoptosis and cell growth, was markedly increased in mineralocorticoid receptor (MR)-positive VSMCs by aldosterone in all microarray, reverse transcriptase-polymerase chain reaction, immunoblotting, and immunofluorescence analyses. In addition, an analysis using small interfering RNA demonstrated that this gene product was involved in cell proliferation of VSMCs induced by aldosterone. Eplerenone, a specific MR antagonist, inhibited this gene induction by aldosterone in VSMCs. MDM2 protein was also more abundant in VSMCs of small resistance arteries in patients with primary aldosteronism compared with a control population. MDM2 is therefore considered one of the mineralocorticoid-responsive genes that regulates cell proliferation of VSMCs induced by MR-mediated aldosterone stimulation, possibly playing an important role in aldosterone-induced vascular structural remodeling.

Effects of aldosterone on transient outward K+ current density in rat ventricular myocytes.

1. Aldosterone, a major ionic homeostasis regulator, might also regulate cardiac ion currents. Using the whole-cell patch-clamp technique, we investigated whether aldosterone affects the 4-aminopyridine-sensitive transient outward K+ current (I(to1)). 2. Exposure to 100 nM aldosterone for 48 h at 37 degrees C produced a 1.6-fold decrease in the I(to1) density compared to control myocytes incubated without aldosterone. Neither the time- nor voltage-dependent properties of the current were significantly altered after aldosterone treatment. RU28318 (1 microM), a specific mineralocorticoid receptor antagonist, prevented the aldosterone-induced decrease in I(to1) density. 3. When myocytes were incubated for 24 h with aldosterone, concentrations up to 1 microM did not change I(to1) density, whereas L-type Ca(2+) current (I(Ca,L)) density increased. After 48 h, aldosterone caused a further increase in I(Ca,L). The delay in the I(to1) response to aldosterone might indicate that it occurs secondary to an increase in I(Ca,L). 4. After 24 h of aldosterone pretreatment, further co-incubation for 24 h either with an I(Ca,L) antagonist (100 nM nifedipine) or with a permeant Ca(2+) chelator (10 microM BAPTA-AM) prevented a decrease in I(to1) density. 5. After 48 h of aldosterone treatment, we observed a 2.5-fold increase in the occurrence of spontaneous Ca(2+) sparks, which was blunted by co-treatment with nifedipine. 6. We conclude that aldosterone decreases I(to1) density. We suggest that this decrease is secondary to the modulation of intracellular Ca(2+) signalling, which probably arises from the aldosterone-induced increase in I(Ca,L). These results provide new insights into how cardiac ionic currents are modulated by hormones.

Aldosterone induces angiotensin-converting-enzyme gene expression in cultured neonatal rat cardiocytes.

The cardiac renin-angiotensin-aldosterone system is activated in failing hearts in proportion to the severity of the disease. We hypothesized that a positive feedback mechanism might exist within this system and contribute to the progression of the heart failure. Methods and Results-- To test this hypothesis, we examined whether angiotensin II or aldosterone induces the expression of angiotensin-converting-enzyme (ACE) mRNA in cultured neonatal rat ventricular cardiocytes. Expression of ACE mRNA was detected and quantified using real-time reverse transcription-polymerase chain reaction. Exposure to angiotensin II (10(-5) mol/L) for 24 hours had no significant effect on the expression of ACE mRNA (0.7+/-0.5-fold versus control, P=NS), but similar treatment with aldosterone (10(-5) mol/L) induced a 23.3+/-7.9-fold increase (P<0.01) in ACE mRNA expression. The effect of aldosterone was both time- (maximal effect, 24 hours) and dose-dependent (EC(50), 4x10(-7) mol/L), and it was significantly (P<0.01) inhibited by spironolactone, a specific mineralocorticoid receptor antagonist. Aldosterone upregulates ACE mRNA expression, which is blocked by spironolactone in neonatal rat cardiocytes. Thus, spironolactone may suppress the progression of heart failure by blocking the effects of aldosterone and angiotensin II.

11 alpha- and 11 beta-hydroxyprogesterone, potent inhibitors of 11 beta-hydroxysteroid dehydrogenase, possess hypertensinogenic activity in the rat.

The progesterone derivatives 11 alpha- and 11 beta-hydroxyprogesterone are potent inhibitors of 11 beta-hydroxysteroid dehydrogenase (isoforms 1 and 2) in vitro and can confer mineralocorticoid activity on corticosterone in the rat in vivo. 11 beta-Hydroxysteroid dehydrogenase metabolizes active glucocorticoids to their inactive 11-dehydro products and protects renal mineralocorticoid receptors from the high circulating levels of endogenous glucocorticoids. 11 beta-Hydroxysteroid dehydrogenase has been suggested to be important not only in the control of renal sodium retention but also of blood pressure. To assess the possible blood pressure-modulating effects of 11 alpha- and 11 beta-hydroxyprogesterone, we infused these substances into both intact and adrenalectomized Sprague-Dawley rats continuously for 14 days. Both 11 alpha- and 11 beta-hydroxyprogesterone caused a significant elevation in blood pressure within 3 days, an effect that persisted throughout the 14-day infusion. The hypertensive effects of 11 alpha-hydroxyprogesterone were abolished by adrenalectomy and significantly attenuated when 11 alpha-hydroxyprogesterone was infused together with the specific mineralocorticoid receptor antagonist RU28318. In an additional series of experiments, 11 alpha-hydroxyprogesterone significantly amplified the hypertensive effects of corticosterone in adrenalectomized spontaneously hypertensive rats but had no effects by itself in this experimental animal. These results demonstrate that both 11 alpha- and 11 beta-hydroxyprogesterone are potently hypertensinogenic in the rat and that this activity depends on an intact adrenal and at least in part on the activation of mineralocorticoid receptors. 11 beta-Hydroxyprogesterone, and similar endogenous progesterone metabolites that inhibit 11 beta-hydroxysteroid dehydrogenase, may be involved in the pathology of certain hypertensive states.

A role for the mineralocorticoid receptor in a rapid and transient suppression of hippocampal 5-HT1A receptor mRNA by corticosterone.

The interaction between corticosterone and hippocampal 5-HT1A receptor mRNA expression was investigated in male rats. Two days after adrenalectomy, 5-HT1A receptor mRNA was increased in the granule cell layer of the dentate gyrus. Injection of corticosterone led to a significant dose-dependent and transient suppression of 5-HT1A receptor mRNA. The effect of a low dose of corticosterone (50 micrograms/kg) could be blocked by RU 28318, a specific mineralocorticoid receptor antagonist, but not by RU 38486, a glucocorticoid antagonist. The effect of a higher dose of corticosterone (300 micrograms/kg) could be partially blocked by RU 28318, whereas there was no additional effect of RU 38486. These results point to a stringent regulation of hippocampal 5-HT1A receptors by corticosterone that is predominantly mediated by the mineralocorticoid receptor.

Central effects of mineralocorticoid antagonist RU-28318 on blood pressure of DOCA-salt hypertensive rats.

The role of brain mineralocorticoid receptor (MR) sites in the pathogenesis of mineralocorticoid hypertension was studied after an intracerebroventricular injection of the MR antagonist RU-28318. Male Wistar rats received subcutaneously implanted deoxycorticosterone acetate (DOCA) pellets and were maintained on 0.9% saline as drinking solution. Under these conditions hypertension developed in approximately 5 wk as assessed in conscious rats by means of the tail-cuff technique. During the development of this hypertension (after 3 wk of DOCA-salt treatment) a single intracerebroventricular injection of the specific MR antagonist RU-28318 reduced systolic blood pressure (SBP) as measured with the tail-cuff method. A decrease in SBP was observed 2-24 h after this intracerebroventricular injection, with the lowest SBP values occurring at 8 h. In these animals (3 wk after DOCA implantation) continuous direct blood pressure recording via chronic cannulation revealed, on the day of the intracerebroventricular injection of RU-28318, a slight increase in arterial pressure during the light phase, followed by a decrease during the dark phase. In the established hypertensive rats (5 wk after DOCA RU-28318 on the arterial pressure or heart rate was detectable. It is concluded that central MR blockade during the development of the DOCA-salt hypertension reduces blood pressure within 24 h assessed with 1) the indirect method at certain time points after exposure to warming and stress and 2) the direct method during the dark phase of the diurnal cycle.

Role of central mineralocorticoid binding sites in development of hypertension

The possibility that central mineralocorticoid binding sites are involved in the development of mineralocorticoid hypertension was examined using chronic blockade of these sites with a specific mineralocorticoid receptor antagonist RU 28318 administered by intracerebroventricular (icv) infusion. The antagonist significantly attenuated the development of deoxycorticosterone acetate (DOCA)-salt hypertension, but the development of one-kidney, one-clip renal hypertension was not affected. This antihypertensive action was attributable to a central action, since intraperitoneal infusion of the same dose of mineralocorticoid antagonist did not alter the peak development of DOCA-salt hypertension. The icv infusion of RU 28318 did not change either the increase of fluid intake induced by DOCA-salt treatment or the pressor reactivity to centrally or peripherally injected arginine vasopressin and angiotensin II and peripherally administered phenylephrine. The antihypertensive action of icv infusion of the mineralocorticoid antagonist was associated with a reduction of neurogenic vasomotor tone and a restoration of impaired arterial baroreflexes. We conclude that functional integrity of central mineralocorticoid binding sites is required for the full development of DOCA-salt hypertension.

Glucocorticoid receptors mediate mineralocorticoid-like effects in cultured collecting duct cells

To investigate the direct epithelial effects of corticosteroids on renal ion transport, we studied the influence of the pure glucocorticoid agonist RU 28362 and aldosterone on Na+ and K+ transport in primary cultures of immunodissected rabbit cortical collecting duct (CCD) cells. When grown on permeable supports in a steroid-free medium, CCD monolayers exhibited a lumen-negative transepithelial potential difference (PD) of 5.2 +/- 1.07 mV and a short-circuit current (SCC) of 8.54 +/- 2.2 microA/cm2. Transepithelial resistance averaged 660 +/- 49 omega/cm2. The cultures actively reabsorbed Na+ and secreted K+. Both aldosterone and RU 28362 significantly increased PD and SCC; the effects were time and dose dependent. The effect of RU 28362 was completely prevented by the glucocorticoid receptor antagonist RU 486, whereas ZK 91587, a specific mineralocorticoid receptor antagonist, did not block its effect. Both aldosterone and RU 28362 increased the bath-to-lumen concentration ratio of Na+ while lowering that of K+, indicating an increased Na+ reabsorption and K+ secretion. The number of Na(+)-K(+)-ATPase units was significantly enhanced (approximately 2-fold) by both RU 28362 and aldosterone. These results demonstrate that, in cultured CCD cells, not only aldosterone but also a pure glucocorticoid is able to exert mineralocorticoid-like effects, and this latter effect is mediated by glucocorticoid receptors. Because all parameters studied responded similarly to aldosterone and RU 28362, we speculate that in CCD cells glucocorticoids and mineralocorticoids might act by regulating the same gene(s).

Central interactions between aldosterone and vasopressin on cardiovascular system.

Although the presence of mineralocorticoid binding sites have been demonstrated in brain, little is known about their physiological role. The purpose of this study was to evaluate possible interactions between a relatively short 2-day central infusion of aldosterone (5 ng/h) and a diverse group of centrally acting pressor agents. The intracerebroventricular infusion of aldosterone selectively attenuated the pressor response produced by the injection of arginine vasopressin (AVP, 10-400 ng) into the lateral ventricle without altering the responses to ventricular administration of 50-200 ng angiotensin II (ANG II), 150 ng carbachol, and 0.5 and 1 M hypertonic sodium chloride. No aldosterone-vasopressin interaction occurred in rats receiving a simultaneous central infusion of aldosterone and RU 28318 [7 beta-hydroxy-3-oxo-7 alpha-propyl(17 alpha)-pregn-4-ene-21-potassium carboxylate], a specific mineralocorticoid receptor antagonist. Baroreflex reactivity and the pressor response to intravenous AVP were not modified by the aldosterone treatment, indicating that overall cardiovascular reactivity was not depressed. Because the vascular reactivity of the mesenteric artery to AVP and norepinephrine remained unchanged after 2 days of central aldosterone infusion, and because plasma levels of aldosterone were not altered, the selective inhibition by this mineralocorticoid of the central AVP response appears to be purely central in origin. This specific central effect of aldosterone is mediated through interaction with mineralocorticoid receptors.