Studies on high affinity binding of mineralo- and glucocorticoids in rabbit aorta cytosol

New roles of aldosterone and mineralocorticoid receptors in cardiovascular disease: translational and sex-specific effects

Recent advances in the field of mineralocorticoid receptor (MR) and its ligand aldosterone expanded the role of this hormone and its receptor far beyond their initial function as a regulator of Na⁺ and K⁺ homeostasis in epithelial cells. The symposium "New Roles of Aldosterone and Mineralocorticoid Receptors in Cardiovascular Disease: Translational and Sex-Specific Effects" presented at the 38th World Congress of the International Union of Physiological Sciences (Rio de Janeiro, Brazil) highlighted the contribution of extrarenal MRs to cardiovascular disease. This symposium showcased how MRs expressed in endothelial, vascular smooth muscle, and immune cells plays a critical role in the development of vascular disease associated with aging, obesity, and chronic aldosterone stimulation and demonstrated that MR antagonism prevents the acute renal dysfunction and tubular injury induced by ischemia-reperfusion injury. It was also shown that the adipocyte-derived hormone leptin is a new direct regulator of aldosterone secretion and that leptin-mediated aldosterone production is a major contributor to obesity-associated hypertension in women. Sex differences in the role of aldosterone and of endothelial MR in the cardiovascular outcomes of obesity were highlighted. This review summarizes these important emerging concepts regarding the contribution of aldosterone and cell-specific MR to cardiovascular disease in male and female subjects and further supports sex-specific benefits of MR antagonist drugs to be tested in additional populations.

Adenosine A2A Receptor Blockade Modulates Glucocorticoid-Induced Morphological Alterations in Axons, But Not in Dendrites, of Hippocampal Neurons

The exposure to supra-physiological levels of glucocorticoids in prenatal life can lead to a long-term impact in brain cytoarchitecture, increasing the susceptibility to neuropsychiatric disorders. Dexamethasone, an exogenous glucocorticoid widely used in pregnant women in risk of preterm delivery, is associated with higher rates of neuropsychiatric conditions throughout life of the descendants. In animal models, prenatal dexamethasone exposure leads to anxious-like behavior and increased susceptibility to depressive-like behavior in adulthood, concomitant with alterations in neuronal morphology in brain regions implicated in the control of emotions and mood. The pharmacologic blockade of the purinergic adenosine A_2A receptor, which was previously described as anxiolytic, is also able to modulate neuronal morphology, namely in the hippocampus. Additionally, recent observations point to an interaction between glucocorticoid receptors (GRs) and adenosine A_2A receptors. In this work, we explored the impact of dexamethasone on neuronal morphology, and the putative implication of adenosine A_2A receptor in the mediation of dexamethasone effects. We report that in vitro hippocampal neurons exposed to dexamethasone (250 nM), in the early phases of development, exhibit a polarized morphology alteration: dendritic atrophy and axonal hypertrophy. While the effect of dexamethasone in the axon is dependent on the activation of adenosine A_2A receptor, the effect in the dendrites relies on the activation of GRs, regardless of the activation of adenosine A_2A receptor. These results support the hypothesis of the interaction between GRs and adenosine A_2A receptors and the potential therapeutic value of modulating adenosine A_2A receptors activation in order to prevent glucocorticoid-induced alterations in developing neurons.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: The role of the mineralocorticoid receptor in the vasculature

Since the mineralocorticoid receptor (MR) was cloned 30 years ago, it has become clear that MR is expressed in extra-renal tissues, including the cardiovascular system, where it is expressed in all cells of the vasculature. Understanding the role of MR in the vasculature has been of particular interest as clinical trials show that MR antagonism improves cardiovascular outcomes out of proportion to changes in blood pressure. The last 30 years of research have demonstrated that MR is a functional hormone-activated transcription factor in vascular smooth muscle cells and endothelial cells. This review summarizes advances in our understanding of the role of vascular MR in regulating blood pressure and vascular function, and its contribution to vascular disease. Specifically, vascular MR contributes directly to blood pressure control and to vascular dysfunction and remodeling in response to hypertension, obesity and vascular injury. The literature is summarized with respect to the role of vascular MR in conditions including: pulmonary hypertension; cerebral vascular remodeling and stroke; vascular inflammation, atherosclerosis and myocardial infarction; acute kidney injury; and vascular pathology in the eye. Considerations regarding the impact of age and sex on the function of vascular MR are also described. Further investigation of the precise molecular mechanisms by which MR contributes to these processes will aid in the identification of novel therapeutic targets to reduce cardiovascular disease (CVD)-related morbidity and mortality.

A Brief Introduction into the Renin-Angiotensin-Aldosterone System: New and Old Techniques

The renin-angiotensin-aldosterone system (RAAS) is a complex system of enzymes, receptors, and peptides that help to control blood pressure and fluid homeostasis. Techniques in studying the RAAS can be difficult due to such factors as peptide/enzyme stability and receptor localization. This paper gives a brief account of the different components of the RAAS and current methods in measuring each component. There is also a discussion of different methods in measuring stem and immune cells by flow cytometry, hypertension, atherosclerosis, oxidative stress, energy balance, and other RAAS-activated phenotypes. While studies on the RAAS have been performed for over 100 years, new techniques have allowed scientists to come up with new insights into this system. These techniques are detailed in this Methods in Molecular Biology Series and give students new to studying the RAAS the proper controls and technical details needed to perform each procedure.

Prevention of aortic and cardiac fibrosis by spironolactone in old normotensive rats

OBJECTIVES

Because the synthesis of aldosterone is mainly modulated by angiotensin II through type I receptor stimulation and because converting enzyme inhibition (CEI) does not modify aortic extracellular matrix in old normotensive rats, the aim of the present study was to determine whether inhibition of aldosterone formation was able to prevent aortic fibrosis in old Sprague-Dawley normotensive rats.

BACKGROUND

We have previously shown that long-term aldosterone antagonism prevents the age-related increase in aortic collagen accumulation in young spontaneously hypertensive rats, independent of blood pressure changes. In contrast, we reported that the positive effects of CEI in the prevention of aortic collagen accumulation were related to the inhibition of angiotensin II actions on angiotensin II type I receptors.

METHODS

For this purpose, we studied the histomorphometric and stiffness (echo-tracking technique) changes of an eight-week treatment with the aldosterone antagonist spironolactone by comparison with placebo.

RESULTS

At the end of treatment, spironolactone in conscious animals did not change intra-arterial blood pressure, aortic and carotid wall thickness, and cardiac weight. Cardiac collagen density and, to a lesser extent, carotid collagen and elastin densities and contents were significantly decreased in association with an increase of carotid distensibility.

CONCLUSIONS

These results show that in old normotensive rats, spironolactone can markedly prevent cardiac and, to a lesser extent, arterial fibrosis and improve arterial stiffness, despite a lack of hypotensive effect.

L-NAME inhibits Mg(2+)-induced rat aortic relaxation in the absence of endothelium

1 L-NG-nitro-arginine methyl ester (L-NAME; 100 microM), a nitric oxide synthase (NOS) inhibitor, reversed the relaxation induced by 3 microM acetylcholine (ACh) and 2-10 mM Mg2+ in endothelium-intact (+E) rat aortic rings precontracted with 1 microM phenylephrine (PE). In PE-precontracted endothelium-denuded (-E) rat aorta, 3 microM ACh did not, but Mg2+ caused relaxation which was reversed by L-NAME, but not by D-NAME. 2 The concentration response profiles of L-NAME in reversing the equipotent relaxation induced by 5 mM Mg2+ and 0.2 microM ACh were not significantly different. 3 L-NAME (100 microM) also reversed Mg(2+)-relaxation of -E aorta pre-contracted with 20 mM KCl or 10 microM prostaglandin F2alpha (PGF2alpha). L-NG-monomethyl-arginine (L-NMMA; 100 microM) was also effective in reversing the Mg(2+)-relaxation. 4 Addition of 0.2 mM Ni2+, like Mg2+, caused relaxation of PE-pre-contracted -E aorta, which was subsequently reversed by 100 microM L-NAME. 5 Reversal of the Mg(2+)-relaxation by 100 microM L-NAME in PE-precontracted -E aorta persisted following pre-incubation with 1 microM dexamethasone or 300 microM aminoguanidine (to inhibit the inducible form of NOS, iNOS). 6 Pretreatment of either +E or -E aortic rings with 100 microM L-NAME caused elevation of contractile responses to Ca2+ in the presence of 1 microM PE. 7 Our results suggest that L-NAME exerts a direct action on, as yet, unidentified vascular smooth muscle plasma membrane protein(s), thus affecting its reactivity to divalent cations leading to the reversal of relaxation. Such an effect of L-NAME is unrelated to the inhibition of endothelial NOS or the inducible NOS.

Prevention of aortic fibrosis by spironolactone in spontaneously hypertensive rats

We have previously shown that long-term angiotensin-converting enzyme (ACE) inhibition prevents the increase in aortic collagen in spontaneously hypertensive rats (SHRs), independent of blood pressure reduction. More recently, we reported that the effects of ACE inhibition in the prevention of aortic collagen accumulation were related to the inhibition of angiotensin II actions on angiotensin II type 1 receptors. Aldosterone, the synthesis of which is mainly modulated by angiotensin II through type 1 receptor stimulation, is known to promote cardiac fibrosis in different experimental models. The aim of the present study was to determine whether inhibition of aldosterone formation was able to prevent aortic fibrosis in SHRs. For this purpose, we compared the effects of a 4-month treatment with the aldosterone antagonist spironolactone with the ACE inhibitor quinapril in 4-week-old SHRs. Control SHRs and Wistar-Kyoto (WKY) rats received placebo for the same period of time. At the end of treatment, in conscious SHRs vs WKY controls, quinapril completely prevented the development of hypertension, whereas spironolactone produced only a slight but significant reduction in blood pressure. Aortic hypertrophy was significantly prevented by ACE inhibition but not by spironolactone. On the contrary, aortic collagen accumulation was completely prevented by both quinapril and spironolactone. In the latter case, collagen density was significantly below that of WKY controls. These results show that in SHRs, spironolactone can markedly prevent aortic fibrosis in the presence of a very slight antihypertensive effect. It is suggested that ACE inhibition or type 1 receptor antagonist-induced prevention of aortic collagen accumulation is at least partially related to aldosterone inhibition.

11 beta-Hydroxysteroid dehydrogenase and the syndrome of apparent mineralocorticoid excess

Whereas aldosterone is normally a much stronger mineralocorticoid than cortisol in vivo, mineralocorticoid receptors have identical in vitro affinities for these hormones. The in vivo specificity of the receptors is, at least in part, the result of activity of 11-HSD, an enzyme located in most mineralocorticoid target tissues that converts cortisol to cortisone. Cortisone is not a ligand for the receptor, whereas aldosterone is not a substrate of the enzyme. The syndrome of AME is a rare form of juvenile hypertension in which 11-HSD is defective. This deficiency allows mineralocorticoid receptors to be occupied by cortisol, leading to hypertension, because plasma concentrations of cortisol are much higher than those of aldosterone. Licorice, which contains 11-HSD inhibitors, causes a similar syndrome. There are two known isozymes of 11-HSD. The liver or type I isozyme is expressed at high levels in the liver, has a relatively low affinity for steroids (micromolar Km), catalyzes both dehydrogenation and the reverse reductase reaction, and utilizes NADP+ or NADPH as cofactors. The kidney or type 2 isozyme is expressed at high levels in the kidney and placenta, has a high affinity (nanomolar Km) for steroids, catalyzes only dehydrogenation, and utilizes NAD+ as a cofactor. Mutations in the HSD11B2 (HSD11K) gene encoding the kidney isozyme of 11-HSD have been detected in all kindreds with AME studied thus far. This gene represents a candidate locus for the common, "essential" form of hypertension.

Intrauterine programming of hypertension by glucocorticoids

An ever increasing body of evidence indicates that cardiovascular disease is determined by prenatal experience of undernutrition. Animal experiments suggest that in addition to maternal dietary interventions, exposure of the fetus to glucocorticoid hormones may programme fetal physiology and metabolism, such that cardiovascular functions are permanently altered. Through nutritional regulation of maternal-placental-fetal hormone interactions long term risk of hypertension may be established long before exposure to adult lifestyle factors more usually associated with cardiovascular mortality.

Histochemical demonstration of 11 beta-hydroxysteroid dehydrogenase in ampullae of semicircular canals

The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) plays a major role in the protection of the mineralocorticoid (type I) receptor. The cellular mechanism of aldosterone selectivity relies on the coexpression of mineralocorticoid receptors and 11 beta HSD in the same cells. An 11 beta HSD activity has been localized in the ampullae of the semicircular canal by histochemical technique which links steroid metabolism with the deposition of formazan deposition. Oxidation of 11 beta-hydroxyandrostenedione was observed in the dark cell region. Oxidation of 11 beta-hydroxyandrostenedione was nicotine-adenine dinucleotide (NAD) dependent. These results demonstrate the presence of a dehydrogenase activity separate from the nicotineamide-adenine dinucleotide phosphate (NADP) dependent 11 beta HSD.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

Corticosteroids in human blood: IX. Evidence for adrenal secretion of sulfate-conjugated cortisol, 11 beta,17 alpha-dihydroxy-4-pregnene-3,20-dione-21-yl-sulfate

A method was developed for the estimation of levels of cortisol-21-sulfate (F KS), cortisone-21-sulfate (ES), and 20(alpha + beta)-reduced cortisol-21-sulfates in blood plasma. Levels of these conjugates were determined in peripheral vein plasma of 42 normal subjects, 21 men, and 21 women (age range 20-64 years) and in adrenal vein plasma of patients with various adrenocortical disorders, six patients with primary hyperaldosteronism, five patients with Cushing's syndrome, and in two obese patients, suspected to have Cushing's syndrome, but with inconclusive laboratory findings. Adrenal vein blood was obtained by percutaneous, trans-femoral adrenal vein catheterization. Levels of non-conjugated (free) cortisol were determined in all plasma samples along with those of the sulfated steroids. F kappa S was found in all plasma samples, both in men and women. The variation in F kappa S levels paralleled that in the free cortisol levels, thus the ratio of F kappa/F kappa S was the same in the blood samples drawn at 8 AM as in those drawn at 4 PM or 5 PM (ranges: 17.5-36.3 in men, 23.6-45.8 in women). The levels of F kappa S were relatively lower in women than in men (women 610-880 ng/100 mL at AM, 300-510 ng/100 mL at PM; men: 760-1,220 ng/100 mL at AM, 380-760 ng/100 mL at PM). Plasma levels of total sulfate-conjugated delta 4-3-keto-C-21 steroids (F kappa S + E kappa S + 20(alpha+beta)-dihydrocortisol-21-sulfates) were 30-40% higher than those of the levels of cortisol-21-sulfate alone (separated by thin-layer chromatography). In the adrenal vein plasma, levels of delta 4-3-keto-C-21-steroid-21-yl sulfates were 20 to 40 times higher than levels of these steroids in the peripheral blood. The bulk of the steroid sulfate measured in the adrenal vein plasma consisted of cortisol-21-sulfate. The ratio of F kappa/F kappa S in the adrenal vein plasma was markedly smaller than in the peripheral vein plasma; it was 6.9-12.3 in males and 4.9-6.7 in females, whereas in the peripheral vein of the same subjects it was 19.2-43.7 in males and 21.4-48.3 in females. Cortisol-21-sulfate isolated from adrenal vein plasma was identified by mass spectrometry. The data presented provide evidence for the secretion of this conjugate by the adrenal cortex. Its secretion appears to be markedly elevated in patients with Cushing's syndrome, both due to hyperplasia and due to adrenal adenoma, as compared with normal subjects and patients with primary aldosteronism, both males and females. However, the F kappa/F kappa S ratio was markedly lower in Cushing's patients due to adrenal adenoma than due to adrenal hyperplasia, this suggesting that ACTH is stimulating intra-adrenal hydrolysis of cortisol sulfate.

Glucocorticoids but not mineralocorticoids modulate endothelin-1 and angiotensin II binding in SHR vascular smooth muscle cells

Both glucocorticoids and mineralocorticoids are involved in circulatory homoeostasis and blood pressure control. In recent years direct effects of both steroid classes on vascular smooth muscle cells (VSMC) have been reported. We have thus examined the effects of RU 28362, a pure glucocorticoid agonist, and aldosterone, the physiologic mineralocorticoid, on the binding to VSMC from spontaneously hypertensive rats (SHR) of two key vasoactive peptides, endothelin-1 and angiotensin II. Binding of angiotensin II rose, and that of endothelin-1 declined, in a time- and dose-dependent fashion with maximal effects observed at 24 h and half-maximal effects for each at 2-3 nM RU 28362. Scatchard analysis showed that for both endothelin-1 and angiotensin II, RU 28362 alters receptor number but not affinity; competition studies with receptor-selective ligands (BQ123, S6C, DuP753 and PD123319) show that glucocorticoids specifically elevate (X2) AT-1 receptors and specifically lower (to approximately 30%) levels of ETA receptors. Treatment of VSMC with the antiglucocorticoid RU 38486 reversed the effect of glucocorticoids on endothelin-1 and angiotensin II binding, confirming the Type II (glucocorticoid) receptor mediated effect of the glucocorticoids. Aldosterone (100 nM) also lowers endothelin-1 binding and increases angiotensin II binding in VSMC; that this effect reflects aldosterone occupancy of classical glucocorticoid receptors is shown by the blockade of the aldosterone effect by an equal concentration (100 nM) of RU 38486--i.e. there is no evidence for an action of aldosterone via mineralocorticoid receptors. We interpret our results as evidence for a complex modulation of receptors for vasoactive peptides in VSMC by glucocorticoid but not mineralocorticoid hormones.

Aldosterone (ALDO) increases transmembrane influx of Na+ in vascular smooth muscle (VSM) cells through increased synthesis of Na+ channels

We have previously reported our studies on glucocorticoid (GC) effects on Na+ influx in vascular smooth muscle (VSM) cells. We now report a parallel study on the effect of mineralocorticoid (MC) on Na+ influx in VSM cells. Unidirectional influx of Na+ was measured in cultured cells of rabbit aortic media with 22Na as tracer. Cells were treated with near physiologic (5 nM) or supraphysiologic (50 nM) aldosterone (ALDO) for 24 or 48 hours, or for 7 to 10 days, in the presence of competitive inhibitors of MC-receptor binding, K-prorenoate (PRN), or GC-receptor binding, RU 486. ALDO at 5 nM increased Na+ influx by 98% +/- 12%, but only after 7-10 days of treatment. This effect was inhibited by PRN, but not by RU 486, and blocked by amiloride but not by ethylisopropyl-amiloride or by dichlorobenzamil (DCB). In VSM cell membranes from aortae of rabbits treated in vivo with ALDO (2 mg/day) for 4 weeks. Na+ channels were quantified by determination of specific [3H]amiloride binding in the presence of excess of DCB and EIPA to exclude tracer binding from the Na+/Ca2+ exchanger and the Na+/H+ antiporter. ALDO doubled the number of of Na+ channels in such isolated cell membranes, as determined by Bmax per mg membrane protein. We propose that this vascular effect of ALDO may constitute an important pathogenetic mechanism of hypertension induced by chronic excess of MC, in addition to the well known renal mechanism.

Organ-specific actions of 11 beta-hydroxysteroid dehydrogenase in humans: implications for the pathophysiology of hypertension

Elucidation of a role for 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) in modulating ligand access to renal mineralocorticoid receptors, together with identification of expression of the enzyme in most mammalian tissues, has raised the possibility (i) that glucocorticoid metabolism might influence corticosteroid receptor activation in other sites which are relevant to blood pressure control (e.g., vascular smooth muscle), and (ii) that abnormal 11 beta-OHSD expression might play a pathogenic role in common forms of hypertension (e.g., essential hypertension and the syndrome of ectopic ACTH secretion). This article reviews data from human experiments which suggest that 11 beta-OHSD has tissue-specific actions which can increase or decrease sensitivity of both mineralocorticoid and glucocorticoid receptors to cortisol, and that assessment of cortisol sensitivity may prove equally important as assessment of cortisol secretion rates in hypertensive patients.

Mechanism of the effects of glucocorticoids and mineralocorticoids on vascular smooth muscle contractility

We have previously demonstrated that receptors to both mineralocorticoids (MC) and glucocorticoids (GC) exist in the arterial wall and that treatment with GC markedly increases Na+ and Ca2+ influx in cultured aortic vascular smooth muscle (VSM) cells, whereas treatment with MC increases only Na+ influx. We now report the results of the study aimed at the elucidation of the mechanism(s) of these effects. Unidirectional influx of Na+ and Ca2+ was measured in cultured cells of rabbit aortic media, using 22Na and 45Ca as tracers, in the presence of ouabain. The cells were treated for different periods with dexamethasone (DEX) or aldosterone (ALDO) in physiologic or supraphysiologic concentrations, in the presence or absence of competitive inhibitors of GC-receptor binding, RU 486, or MC-receptor binding, K-prorenoate. DEX in 50 nM concentration increased Na+ influx by 98 +/- 18% and Ca2+ influx by 100 +/- 20%, and the maximum effect was seen after 48 hour cell-treatment. ALDO in 5 nM concentration increased Na+ influx by 90 +/- 12% and had no effect on Ca2+ influx, and the maximum effect was seen after 7-10 days of cell-treatment. The enhancing effect of both DEX and ALDO on the influx rate of Na+ was prevented by actinomycin D and by cycloheximide. RU 486 completely inhibited DEX from exercising its enhancing effect on Na+ influx, but diminished influx rate of Na+ increased by ALDO only by 25%. Prorenoate (PRN) did not have any effect on DEX-increased Na+ influx, but completely inhibited ALDO from exercising its effect.(ABSTRACT TRUNCATED AT 250 WORDS)

11 beta-Hydroxysteroid dehydrogenase activity in mesenteric arteries of spontaneously hypertensive rats

1. 11 beta-Hydroxysteroid dehydrogenase (11-HSD) activity in mesenteric arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats was determined and expressed as the percentage conversion of [3H]-corticosterone to [3H]-11-dehydrocorticosterone. 2. 11-HSD activity was significantly decreased in mesenteric arteries of both 4 and 9 week old SHR (8.4 +/- 0.8%, 5.0 +/- 1.5%, respectively) compared with WKY rats (12.4 +/- 0.6%, 15.8 +/- 0.7%, respectively; P < 0.05). 3. Total RNA from rat vascular smooth muscle cells (VSMC) and endothelial cells (EC) were prepared with selective precipitation in 3 mol/L LiCl/6 mol/L urea. The expression of 11-HSD mRNA was confirmed in the rat VSMC but its mRNA expression was not detected in EC, using northern blot analysis. 4. The results in this study indicate that 11-HSD in the vascular wall may play a role in the pathogenesis of hypertension in SHR.

The role of vascular steroid receptors in the control of vascular contractility and peripheral vascular resistance

Evidence is presented that glucocorticoids (GC) and mineralocorticoids (MC) control contractility of vascular smooth muscle (VSM). This control is effected through the in situ mechanism for the action of these steroids in the arterial and arteriolar wall. This action is mediated through GC and MC receptors in the VSM cell. Acting through these receptors, MC and GC increase transport capacities of different transmembrane transport systems for Na+ and/or Ca2+ through induction of synthesis of proteins constituting the transport systems. Colocalization of enzymes deactivating cortisol in VSM, with VSM receptors for GC and MC further strengthens the concept that the arterial network houses an in situ molecular mechanism for the control of VSM contractility, thus peripheral vascular resistance.

Immunohistochemical and biochemical evidence for a cardiovascular mineralocorticoid receptor

The presence of mineralocorticoid receptors (MRs) and their physicochemical characteristics were investigated in the heart and blood vessels of rabbits. Immunohistochemical methods using the monoclonal anti-idiotypic antibody H10E, which interacts with the steroid binding domain of MRs, revealed the presence of immunoreactive material in the heart and large blood vessels. In the heart, a positive staining was observed in myocytes and endothelial cells of atria and ventricles. In vessels, MRs were detected in the aorta and pulmonary artery. They were localized in endothelial and vascular smooth muscle cells. No staining was present in the small vascular bed, arterioles, and capillaries. In all these studies, the mineralocorticoid specificity of the staining was assessed by in situ competition experiments with aldosterone and RU486, a glucocorticoid antagonist. The presence of MRs in the heart and vessels was further demonstrated by specific aldosterone binding to one class of high affinity binding sites in the cytosol of the adrenalectomized rabbit heart (Kd, 0.25 nM; maximum MR concentration, 15-20 fmol/mg protein), whose mineralocorticoid specificity has been clearly established by competition studies. Sedimentation gradient analyses revealed that the cardiovascular MR is an 8.5S hetero-oligomer that includes the heat shock protein 90. The physicochemical characteristics of the cardiovascular MRs are virtually identical to those of the renal MRs. Altogether, our results clearly demonstrate the presence of MRs in the cardiovascular system. This supports the possibility of direct aldosterone actions in the heart and blood vessels.

The influence of glucocorticoids on the growth of a human leiomyosarcoma cell line SK-LMS-1

A cell line derived from a human leiomyosarcoma, SK-LMS-I, has cystolic [Bmax 201.6 +/- 39.7, means +/- SD, fm/mg cytosol protein KD 14.6 +/- 7.8 nM (n = 8)] and nuclear [Bmax 189.2 +/- 87.3 fM/mg DNA, KD 4.8 +/- 0.26 nM (n = 5)] glucocorticoid receptor, by Scatchard analysis of tumors grown in male athymic mice. Tumor growth of SK-LMS-I cells in male athymic mice is inhibited by daily s.c. injection of DEX 5 micrograms, DEX 25 micrograms, DEX 5 micrograms with 5 mu RU-486 and 5 micrograms RU-486. In sharp contrast, in vitro, glucocorticoid markedly stimulates the growth (as determined by cell number) of SK-LMS-I cells, principally at higher cell densities (days 10-21 of growth carried on over a 21- to 23-day period), the greatest stimulation being seen with DEX 10(-6) to 10(-8) M, and no stimulation being seen with DEX 10(-9) and 10(-10) M. In vitro, glucocorticoids with higher affinity for the GR stimulate growth, steroids with lower affinity inhibit growth. No alterations in cell-cycle distribution (percent G0/G1, S, or G2/m) could be found by flow cytometric analysis of glucocorticoid-stimulated asynchronously growing cultures. Single, isolated, untreated SK-LMS-I cells form colonies in soft agar with an efficiency of 1.78 +/- 0.10%. Pre-treatment of cells with DEX 10(-7) M increases this to 3.24 +/- 0.17%, while cells pre-treated with both DEX 10(-7) M RU-486 10(7) M form colonies with the same efficiency as untreated cells. Glucocorticoids have inhibitory effects on in vivo growth and stimulatory effects on in vitro growth of a GR-positive human leiomyosarcoma cell line.

Racial differences in aldosterone excretion and plasma aldosterone concentrations in children

Blacks are more likely to have hypertension, have lower levels of plasma renin activity, and typically consume less potassium than whites. Whether blacks and whites secrete different amounts of aldosterone is less clear. We estimated aldosterone secretion indirectly in 715 children, 249 of whom were black, by measuring their nocturnal rates of urinary excretion of aldosterone. Dietary sodium and potassium intakes were estimated from their excretion rates. The mean (+/- SE) aldosterone-excretion rate was lower in the black children than in the white children (0.045 +/- 0.003 vs. 0.078 +/- 0.004 nmol per micromole of creatinine per kilogram of body weight; P less than 0.001). The potassium-excretion rate was also lower in the black children than in the white children (0.13 +/- 0.01 vs. 0.18 +/- 0.01 mmol per micromole of creatinine per kilogram; P less than 0.001). Aldosterone excretion was highly correlated with potassium excretion (P less than 0.001), but the lower aldosterone-excretion rate in blacks was explained only in part by their lower dietary intake of potassium. Systolic blood pressure was higher in black children (P less than 0.001), as was diastolic pressure (P = 0.037). In a second study of 99 children, the plasma aldosterone level was found to be significantly lower in black children than in white children (230 +/- 30 vs. 400 +/- 30 pmol per liter; P less than 0.001). Plasma renin activity and plasma cortisol levels were the same in both groups. In summary, we found that black children secrete about 40 percent less aldosterone than white children. The role of the lower aldosterone-secretion rate in the genesis of the higher blood pressures observed in black children is not known.

Detection of corticosteroid type I binding sites in heart

Both high affinity (type I) and low affinity (type II) corticosteroid binding sites are detected in cytosolic extracts of atrial and ventricular tissue when [3H]aldosterone is used as the ligand. In the presence of RU-28362, which blocks binding of [3H]hormone to the low affinity type II sites, [3H]aldosterone binds to a single class of high affinity sites. The apparent Kd for binding of the hormone to the type I sites was 1.0 nM in atrial cytosol and 0.75 nM in ventricular cytosol. The concentration of type I sites in atrial (12 fmol/mg protein) and ventricular cytosols (11 fmol/mg protein) is comparable to reported values in renal (17-31 fmol/mg protein) cytosol. Activation of the type I hormone-receptor complexes to the DNA-binding form was examined using chromatography on DEAE-Sephadex anion-exchange resin. The unactivated hormone-receptor complex elutes at a concentration of 400 mM KCl. Following heat treatment (25 degrees C, 30 min) the [3H]aldosterone-receptor complex is transformed to a low salt eluting (200 mM KCl), DNA-binding form. Activation is blocked by inclusion of 10 mM sodium molybdate during heat treatment.

The role of arterial mineralocorticoid receptors in the mechanism of hypertension: findings and hypothesis

Alterations in electrolyte transport across cell membrane of vascular smooth muscle (VSM) and changes in hemodynamics [increased extracellular fluid volume (ECFV) and cardiac output (C.O.)] have been implicated in the pathogenetic mechanisms of both mineralocorticoid-induced hypertension (MH) and essential hypertension (EH). We have previously found that mineralocorticoids (MC) can act directly on arterial wall by means of a receptor-mediated mechanism, and have postulated that this mechanism is of critical importance in the increased reactivity of VSM to vasoconstrictive stimuli in MH. We now present evidence that a MC-antagonist at the MC-receptor level, progesterone, prevents induction of changes in VSM cell-membrane permeability to Na+ by MC, and development of hypertension. This study has been carried out on rabbits made hypertensive by s.c. implantation of silastic rubber strips impregnated with 11-desoxycorticosterone (the inducer) and/or 50 times that amount of progesterone (the anti-inducer). We hypothesize that the VSM cell-membrane defect (MC-induced in MH and congenital in EH) initiates two separate sequences of biochemical events. One leads, in early stages of hypertension, to expansion of ECFV, increase in C.O., myogenic vasoconstriction and hypertension. When kidney function matures, hypertension recedes. The second sequence of events leads to hypertension via an increase in [Na]i of VSM, leading to an increase in [Ca]i, and an increased contractility of VSM. This hypertension persists. The two sequences are concomitant but independent of each other.

Functions and dysfunctions of receptors for adrenal corticoids in the central nervous system

Glucocorticoids (GC) have several known effects on the function of the nervous system, and GC receptors have been identified in regions responding to hormonal action. In the spinal cord, GC receptors have been characterized in vitro, which share several biochemical properties in common with receptors in better studied areas such as the hippocampus. Moreover, enzymes which are induced by GC in the hippocampus, such as glycerolphosphate dehydrogenase and ornithine decarboxylase, are also under specific GC control in the spinal cord. Yet GC receptors in the latter tissue divert from those in hippocampus during some in vivo as well as in vitro studies. In vivo, uptake of [3H]corticosterone by purified cell nuclei was 5-8-fold higher in the hippocampus as compared to the cord. In vitro, a higher percentage of GC receptors previously transformed by heating, showed affinity towards DNA-cellulose in the spinal cord than in the hippocampus. The enzyme RNAse A effectively increased receptor binding to DNA-cellulose in hippocampus, whereas the cord was insensitive to its action. These results suggest that there is a "receptor dysfunction" in the spinal cord, the significance of which is poorly understood in terms of the accepted model of steroid hormone action.

A physico-chemical comparison of aortic receptors in rat hypertension models

Rat models of genetic hypertension include spontaneous hypertension and resistance or sensitivity to mineralocorticoid and salt induced hypertension. Previously, altered aldosterone binding to corticoid receptor I was found in aortic smooth muscle cells cultured from Fischer 344 rats which are extremely resistant to steroid and salt induced hypertension. The corticoid receptor I of Fisher 344 rats had a lower affinity than that of salt sensitive Wistar-Kyoto controls, as well as spontaneously hypertensive rats and Sprague-Dawley rats. In the present study, we have used DEAE-cellulose ion exchange chromatography to compare the structure (charge properties) and steroid specificity of vascular corticoid receptor I and II sites in these same rat hypertension models. No variations in ion exchange properties of type I and II receptors were found. Together with the lower aldosterone affinity of corticoid receptor I sites in Fischer 344 rats these data suggest an altered binding domain which is not seen as a difference in charge density of the receptor protein by ion exchange chromatography.

Comparison of aldosterone binding in aortic cells from Dahl salt-susceptible and salt-resistant rats

The Dahl salt-resistant substrain of Sprague-Dawley rats represents a uniform population of animals that are resistant to salt and mineralocorticoid induced hypertension. Aldosterone binding in the aortae of these rats is contrasted to that of age- and sex-matched rats of the Dahl salt-susceptible strain in an effort to identify a mechanism for resistance to salt induced hypertension. Cultured smooth muscle cells of both substrains contain two classes of aldosterone binding sites: corticoid receptor I with high affinity and low capacity, and corticoid receptor II with low affinity and high capacity. No differences were found between the two substrains in the affinities or binding capacities of these receptors. Both groups of Sprague-Dawley rats had a significantly higher corticoid receptor I affinity than the salt resistant Fischer 344 rats, a strain with a two-fold lower affinity than salt sensitive strains. These results indicate that an intrinsic defect in mineralocorticoid binding in aortic smooth muscle cells could not account for the resistance to salt and mineralocorticoid induced hypertension seen in Sprague-Dawley rats and that the biochemical abnormality underlying salt resistance is likely to be different from that of Fischer 344 rats.

Temperature dependence of ionic transport and norepinephrine stimulation of rat aorta during DOCA hypertension

Temperature perturbation was used to determine whether increased turnover of Na, K, and Cl at 37 degrees C in aortas from rats made hypertensive with deoxycorticosterone acetate salt treatment (DOCH) reflects an increased number of transport sites that individually maintain relatively normal function. Decreasing temperature reduced the resting effluxes of 42K, 36Cl, and 24Na (active and passive) from control and DOCH in parallel fashion. The slope of the Arrhenius plots (activation energies) and the transition temperatures at which major changes in slope occurred were similar in controls and DOCH. In contrast to the results for resting effluxes, the temperature dependence for the effects of norepinephrine (NE) on contraction and on 42K and 36Cl effluxes in DOCH differed from controls. At 20 degrees C, the responses to NE were either abolished or greatly suppressed in DOCH, as compared to controls, while no significant differences between the two groups were observed at 30 degrees C. These results indicate that alterations in resting 42K, 36Cl, and 24Na effluxes in DOCH may result from an increased number of transport sites in the membranes of vascular smooth muscle. The concept that alterations occurred in the integral components of the membrane is also supported by the observation that increased resting 42K and 36Cl effluxes in DOCH at 37 degrees C persisted in aortas that had undergone cold storage for 2 days before incubation at 37 degrees C. The altered temperature dependence for the effects of NE on DOCH, compared to controls, indicates that the involvement of agonist-receptor-membrane events may be dissociated from the alterations in resting ionic fluxes.

Influence of adrenalectomy and steroid replacement on heart citrate synthase levels

Aldosterone-dependent changes in citrate synthase (CS) activity have been used as an index of mineralocorticoid target sites. However, adrenalectomy (ADX) resulted in a fall in activity of CS and several other enzymes in rabbit heart, a tissue with glucocorticoid-but not mineralocorticoid-specific receptors. The enzymes included CS (2.03-1.36 U/mg protein, normal----ADX, P less than 0.001), isocitrate dehydrogenase-NADP+ (1.10-0.80 U/mg, P less than 0.002), isocitrate dehydrogenase-NAD+ (0.034-0.020 U/mg, P less than 0.01), and hydroxymethylglutaryl-CoA lyase (0.072 to 0.035 U/mg, P less than 0.001); in contrast, mitochondrial malate dehydrogenase levels were not significantly reduced by adrenal loss. There was also a decrease after surgery in sarcolemmal Na-K-(17.30-12.31 mumol Pi . mg protein-1 . h-1, P less than 0.002) and Mg-ATPase activities (14.16-12.11 mumol Pi . mg protein-1 . h-1, P less than 0.05). However, ADX did not result in a significant change in heart weight per kilogram body weight or recovery of mitochondrial protein per gram heart. CS was also assayed in hearts from ADX animals following acute (90 min) and chronic (3 day) steroid replacement. Although neither acute intravenous aldosterone (10 micrograms/kg) nor dexamethasone (100 micrograms/kg) increased activity, exposure to multiple subcutaneous injections of either steroid over a 3-day period significantly elevated CS above ADX values. The coordinate changes in the levels of several myocardial enzymes associated with energy metabolism is discussed in terms of an adaptation to chronic alterations in energy demands as opposed to specific mineralocorticoid or glucocorticoid receptor-mediated processes.

Aldosterone-binding globulin-induced hypertension in the rat. A new experimental model

A thermostable urinary homologue of the plasma aldosterone-binding globulin (ABG), designated ABG-TsU, was isolated and purified by differential ultrafiltration, ion exchange chromatography, and gel filtration to electrophoretic homogeneity. Scatchard plot analysis using highly purified ABG-TsU demonstrated reversible high-affinity low-capacity binding at separate sites for aldosterone and dehydroepiandrosterone sulfate (DHEA-SO4). ABG-TsU injected intraperitoneally (i.p.) in male rats resulted in sustained hypertension after 5 to 8 days, characterized after 12 days by no changes in plasma Na+ K+, aldosterone, or plasma renin activity (PRA). No histological changes could be detected in the kidneys, brains, or hearts, nor evidence of adrenocortical hyperplasia. This hypertension appears to be aldosterone-dependent since it is prevented by bilateral adrenalectomy or administration of a spironolactone, but not by adrenalectomy when aldosterone is given concomitantly with ABG-TsU. Hemodynamic characterization of this hypertension was carried out in rats after treatment with ABG-TsU or saline i.p. for 14 days. Cardiac output (CO) was measured using the reference sample microsphere method. ABG-TsU-treated rats had significantly higher mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), and CO, while no difference in total peripheral resistance (TPR) was detected. This new animal model of borderline essential hypertension (EH) induced by ABG-TsU, which has a reversible high-affinity binding for aldosterone, results in adrenal-dependent hypertension due at this early phase to an increase in CO without any change in TPR, which remains inappropriately normal.