Blood pressure changes following chronic administration to rats of 3beta,16beta-dihydroxy-5-androsten-17-one, 3beta,17beta-dihydroxy-5-androsten-16-one and 21-hydroxy-4-pregnene-3,20-dione-21-acetate.

The urinary excretion of 3beta,16beta-dihydroxy-5-androsten-17-one (16beta-OH-DHEA) is increased in patients with low renin essential hypertension. This steroid and its isomer 3beta,17beta-dihydroxy-5-androsten-16-one (16-oxo-A) have also been reported to have mineralocorticoid activity in adrenalectomized rats. These findings have led to the postulate that excessive secretion of 16beta-OH-DHEA may be responsible for the production of low renin essential hypertension. In this study unilaterally nephrectomized salt loaded rats injected once a week with 30 mg of 11-desoxycorticosterone acetate per/kg of body weight for 2 month periods developed hypertension. Rats given similar amounts of 16beta-OH-DHEA or 16-oxo-A and rats given no steroids did not develop hypertension. We conclude that it is unlikely that 16beta-OH-DHEA and 16-oxo-A are direct causative factors in the production of low renin essential hypertension.     

Effects of Adrenal Steroids on Basal Ganglia Neuropeptide mRNA and Tyrosine Hydroxylase Radioimmunoreactive Levels in the Adrenalectomized Rat

Abstract: To investigate the effects of type I (mineralocorticoid) and type II (glucocorticoid) receptor activation on striatal neuropeptide [preproenkephalin (PPE), preprotachykinin (PPT), and preprodynorphin (DYN)] mRNA and midbrain cholecystokinin (CCK) mRNA as well as striatal tyrosine hydroxylase radioimmunoreactivity (TH-RIC) levels, we administered either replacement levels of corticosterone (CORT; 0.5 mg/kg/day, s.c.) or pharmacological levels of deoxycorticosterone acetate (DOCA; a mineralocorticoid steroid with ability to bind to type I and type II receptors; 5 mg/kg, s.c.) to adrenalectomized adult male rats. After 1 week of recovery from adrenalectomy surgery, animals were injected daily with sesame oil or CORT for 1, 3, or 7 days or DOCA for 3 or 7 days and killed 16 h after the last injection. Adrenalectomy resulted in a decrease in all three striatal neuropeptide mRNA levels, compared with sham-operated rats. CORT replacement resulted in recovered PPE and PPT mRNA levels after 1 day and elevated PPE mRNA levels over those in sham-operated controls after 3 days. In contrast, DYN mRNA levels showed recovery after 7 days of CORT replacement. Results after DOCA treatment largely paralleled those after CORT replacement. There were no significant treatment effects on indirect markers of midbrain dopaminergic activity, i.e., CCK mRNA and TH-RIC. From these results we conclude that compared with striatal tachykinin and dynorphinergic neurons, enkephalinergic cells show greater sensitivity, whereas the dopaminergic system, including mesencephalic CCK, demonstrates an insensitivity to physiological CORT and to pharmacological DOCA treatment.     

Elevated cardiac tissue level of aldosterone and mineralocorticoid receptor in diastolic heart failure: Beneficial effects of mineralocorticoid receptor blocker

Cardiac aldosterone levels have not been evaluated in diastolic heart failure (DHF), and its roles in this type of heart failure remain unclear. This study aimed to detect cardiac aldosterone by use of a liquid chromatographic-mass spectrometric method and to assess the effects of mineralocorticoid receptor blockade on hypertensive DHF. Dahl salt-sensitive rats fed 8% NaCl diet from 7 wk (hypertensive DHF model) were divided at 13 wk into three groups: those treated with subdepressor doses of eplerenone (12.5 or 40 mg x kg(-1) x day(-1)) and an untreated group. Dahl salt-sensitive rats fed 0.3% NaCl diet served as controls. Cardiac aldosterone was detected in the DHF rats but not in the control rats, with increased ventricular levels of mineralocorticoid receptor. Cardiac levels of 11-deoxycorticosterone, corticosterone, and 11-dehydrocorticosterone were not different between the control and DHF rats, but the tissue level of corticosterone that has an affinity to mineralocorticoid receptor was 1,000 times as high as that of aldosterone. Aldosterone synthase activity and CYP11B2 mRNA were undetectable in the ventricular tissue of the DHF rats. Administration of eplerenone attenuated ventricular hypertrophy, ventricular fibrosis, myocardial stiffening, and relaxation abnormality, leading to the prevention of overt DHF. In summary, the myocardial aldosterone level increased in the DHF rats. However, its value was extremely low compared with corticosterone, and no evidence for enhancement of intrinsic myocardial aldosterone production was found. The upregulation of mineralocorticoid receptor may play a central role in the pathogenesis of DHF, and blockade of mineralocorticoid receptor is likely an effective therapeutic regimen of DHF.     

Equivalent affinity of aldosterone and corticosterone for type I receptors in kidney and hippocampus: direct binding studies

In studies from several laboratories evidence has been adduced that renal Type I (mineralocorticoid) receptors and hippocampal "corticosterone-preferring" high affinity glucocorticoid receptors have similar high affinity for both aldosterone and corticosterone. In all these studies the evidence for renal mineralocorticoid receptors is indirect, inasmuch as the high concentrations of transcortin (CBG) in renal cytosol make studies with [3H]corticosterone as a probe difficult to interpret, given its high affinity for CBG. We here report direct binding studies, with [3H]aldosterone and [3H]corticosterone as probes, on hippocampal and renal cytosols from adrenalectomized rats, in which tracer was excluded from Type II dexamethasone binding glucocorticoid receptors with excess RU26988, and from CBG by excess cortisol 17 beta acid. In addition, we have compared the binding of [3H]aldosterone and [3H]corticosterone in renal cytosols from 10-day old rats, in which CBG levels in plasma and kidney are extremely low. Under conditions where neither tracer binds to type II sites or CBG, they label an equal number of sites (kidney 30-50 fmol/mg protein, hippocampus approximately 200 fmol/mg protein) with equal, high affinity (Kd 4 degrees C 0.3-0.5 nM). Thus direct tracer binding studies support the identity of renal Type I mineralocorticoid receptors and hippocampal Type I (high affinity, corticosterone preferring) glucocorticoid receptors.     

Comparative analysis of mineralocorticoid receptor expression among vocal learners (Bengalese finch and budgerigar) and non-vocal learners (quail and ring dove) has implications for the evolution of avian vocal learning

Mineralocorticoid receptor is the receptor for corticosteroids such as corticosterone or aldosterone. Previously, we found that mineralocorticoid receptor was highly expressed in song nuclei of a songbird, Bengalese finch (Lonchura striata var. domestica). Here, to examine the relationship between mineralocorticoid receptor expression and avian vocal learning, we analyzed mineralocorticoid receptor expression in the developing brain of another vocal learner, budgerigar (Melopsittacus undulatus) and non-vocal learners, quail (Coturnix japonica) and ring dove (Streptopelia capicola). Mineralocorticoid receptor showed vocal control area-related expressions in budgerigars as Bengalese finches, whereas no such mineralocorticoid receptor expressions were seen in the telencephalon of non-vocal learners. Thus, these results suggest the possibility that mineralocorticoid receptor plays a role in vocal development of parrots as songbirds and that the acquisition of mineralocorticoid receptor expression is involved in the evolution of avian vocal learning.     

19-Noraldosterone in pregnancy-induced hypertension

Pregnancy-induced hypertension (PIH) is a frequent cause of maternal and neonatal morbidity and mortality. 19-Noraldosterone, which was shown to be synthesized in the human adrenal gland, exhibits potent mineralocorticoid and hypertensive activity. To examine the role of mineralocorticoids in the pathophysiology of PIH, we studied urinary 19-noraldosterone, tetrahydroaldosterone, free cortisol, and cortisone concentrations and mineralocorticoid receptor levels in peripheral blood mononuclear leukocytes, from 17 women with PIH and 16 normal pregnant women as controls. Sequence analysis of the mineralocorticoid receptor gene in PIH patients was also done. The 24-h urinary excretion of 19-noraldosterone was significantly lower in PIH (120 +/- 38 pmol/day) than in controls (358 +/- 55 pmol/day) (P < 0.05). Urinary tetrahydroaldosterone was also decreased in PIH compared with controls. Ratios of urinary free cortisol to cortisone (a measure of 11beta-hydroxysteroid dehydrogenase 2 activity) did not differ significantly between groups. Mineralocorticoid receptor density was significantly (P < 0.05) decreased in the PIH group (133 +/- 15 binding sites/cell) compared with controls (255 +/- 21 binding sites/cell). No mutations were found in the coding region of the mineralocorticoid receptor gene in PIH. These results suggest that circulating aldosterone, 19-noraldosterone, and renal 11beta-hydroxysteroid dehydrogenase2 do not contribute to the pathogenesis of PIH. Regulatory factors that cause the down-regulation of the mineralocorticoid receptor in PIH should be clarified.     

Effect of 9 alpha-fluorocortisol on the excretion of urinary digoxin-like substance in normotensive men

In order to investigate the possible role of mineralocorticoid in the regulation of digoxin-like substance (DLS), 9 alpha-fluorocortisol (9-F) was administered to 6 healthy men and urinary excretion of DLS was measured. The administration of 0.6 mg of 9-F caused slight increases in body weight and blood pressure and significant decreases in urinary Na excretion, plasma renin activity and plasma aldosterone, which indicate the expansion of extracellular fluid (ECF) volume by 9-F administration. Urinary excretion of DLS decreased significantly from the baseline level of 43.3 +/- 2.6 (SEM) to 29.8 +/- 5.1 (SEM) ng/day; digoxin equiv. after 9-F. These results suggest that a large dose of mineralocorticoid may suppress DLS despite an increase in the ECF volume.     

Calcium metabolism and mineralocorticoid-induced hypertension: effects of parathormone and exogenous thyrocalcitonin and of variations in dietary calcium and magnesium]

Physiological doses of parathyroid extract producing normal serum calcium level restore mineralocorticoid hypertension development in parathyroidectomized or thyroparathyroidectomized rats, supplemented with thyroid hormones. On the other hand, increased calcium or magnesium in dietary moderates hypertension development. Those results confirm the participation of parathyroids during mineralocorticoid hypertension.     

Dose-dependent action of corticosteroids on brain serotonin content and passive avoidance behavior.

Corticosterone, 1.0 and 5.0 mg/kg, improved passive avoidance behavior based on fear versus thirst-conflict situation. Corticosterone, 1.0 mg/kg, increased the serotonin (5-HT) content in the hypothalamus and mesencephalon; 5.0 mg/kg of corticosterone had no effect. Plasma corticosterone level increased in a dosedependent manner after corticosterone treatment. dl-Parachlorophenylalanine (PCPA) impaired passive avoidance behavior and decreased the hypothalamic and mesencephalic 5-HT level. After PCPA treatment, the plasma corticosterone level was slightly increased. PCPA pretreatment was able to prevent the action of 1.0 and 5.0 mg/kg of corticosterone on behavior as well as on brain 5-HT level. Corticosterone, 10.0 mg/kg, impaired passive avoidance behavior, decreased the hypothalamic and mesencephalic 5-HT content, and increased the plasma corticosterone level.Monoamine oxidase inhibitor (nialamide) treatment improved the passive avoidance behavior and increased the 5-HT level in the hypothalamus and mesencephalon. The plasma corticosterone level did not change significantly. Nialamide pretreatment abolished the behavioral action of 10.0 mg/kg of corticosterone as well as its action on brain 5-HT level. A large dose of corticosterone (25.0 mg/kg) and 2.5 mg/kg of 6-dehydro-16-methylenhydrocortisone (6DH) had a similar action on passive avoidance behavior and on brain serotonin level as 10.0 mg/kg of corticosterone; however, the plasma corticosterone level was increased only in corticosterone-treated animals and was significantly decreased after 6DH. 11-Deoxycorticosterone (DOC) at a dose of 25.0 mg/kg was ineffective on passive avoidance behavior and on brain serotonin content, whereas it slightly decreased the plasma corticosterone level. Data suggest that the corticosterone has dosedependent dual action on passive avoidance behavior, and its action is, at least partly, mediated via changed brain serotonin metabolism. The action seems to be a glucocorticoid-specific one since mineralocorticoid (DOC) is ineffective on this behavioral pattern.     

Blood pressure and metabolic effects of 18-oxo-cortisol in sheep

18-Oxo-cortisol (18-oxo-F) has been isolated from the urine of subjects with primary aldosteronism. This study examines the pressor, mineralocorticoid and glucocorticoid effects of 18-oxo-F in conscious sheep--a well studied species for the assessment of the pressor effect of steroid hormones. 18-oxo-F (24 mg/day i.v. for 5 days, n = 3) increased mean arterial pressure MAP (64 +/- 2 mmHg control and 75 +/- 6 mmHg on day 5 P less than 0.001). There was no change in heart rate. Plasma [K+] decreased from a control of 4.3 +/- 0.1 mmol/l control to 2.9 +/- 0.3 mmol/l on day 5 (P less than 0.001). Urinary Na+ excretion decreased on the first infusion day (233 +/- 18 mmol/day control and 124 +/- 20 mmol/day on infusion day 1 P less than 0.001). Urinary K+ excretion was reduced on days 1, 4 and 5 of the infusion. Thus in sheep, 18-oxo-F increased blood pressure associated with in vivo evidence of mineralocorticoid activity.     

Endocrine and antitumoral effects of R76713 in rats

Some effects of daily oral administration of a new non-steroidal aromatase inhibitor on the pituitary-gonadal and adrenal functions were investigated in female rats. At doses of 1 mg/kg twice daily or higher, R 76713 lowered plasma estradiol levels to the range measured after ovariectomy Plasma progesterone levels and uterine weights decreased whilst LH levels increased but to a lesser extent than after ovariectomy. The other hormonal data show that long-term administration of R 76 713 does not modify the gluco- and mineralocorticoid hormone levels even at the highest dose studied (20 mg/kg, 4 h after treatment). Furthermore, both ovariectomy and R 76 713 treatment (1 and 5 mg/kg twice a day) induced almost complete regression of 9,12-dimethyl-1,2-benzanthracene-induced mammary carcinoma in rats. The appearance of new tumors during the treatment period was completely inhibited by R 76 713 whilst multiplicity of the remaining tumors was dramatically reduced.     

Differential effects of mineralocorticoid and angiotensin II on incentive and mesolimbic activity

The controls of thirst and sodium appetite are mediated in part by the hormones aldosterone and angiotensin II (AngII). The present study examined the behavioral and neural mechanisms of altered effort-value in animals treated with systemic mineralocorticoids, intracerebroventricular AngII, or both. First, rats treated with mineralocorticoid and AngII were tested in the progressive ratio operant task. The willingness to work for sodium versus water depended on hormonal treatment. In particular, rats treated with both mineralocorticoid and AngII preferentially worked for access to sodium versus water compared with rats given only one of these hormones. Second, components of the mesolimbic dopamine pathway were examined for modulation by mineralocorticoids and AngII. Based on cFos immunohistochemistry, AngII treatment activated neurons in the ventral tegmental area and nucleus accumbens, with no enhancement by mineralocorticoid pretreatment. In contrast, Western blot analysis revealed that combined hormone treatment increased levels of phospho-tyrosine hydroxylase in the ventral tegmental area. Thus, mineralocorticoid and AngII treatments differentially engaged the mesolimbic pathway based on tyrosine hydroxylase levels versus cFos activation.     

Structural, functional and hypertensive effects of 19-oxo-11-deoxycorticosterone acetate (19-oxo-DOCA) in the rat

Mononephrectomized rats were given 1% NaCl solution to drink; half of them received 1 mg/day of 19-oxo-11 deoxycorticosterone acetate (19-oxo-DOCA) in sesame oil subcutaneously and half received only the oil for a period of four weeks. The steroid had no effect upon saline intake, systolic blood pressure, growth or the size of adrenals, hearts or kidneys, although it did produce hypernatremia and hypokalemia. The discrepancy between a demonstrable mineralocorticoid effect without blood pressure elevation awaits elucidation.     

A new affinity matrix for mineralocorticoid receptors

The behavior of mineralocorticoid and glucocorticoid receptors of rabbit kidney cytosol was investigated on two affinity gels: a new affinity matrix prepared with a 3-O-derivative of carboxymethyloxime deoxycorticosterone (deoxycorticosterone gel) and a gel linked to a 17 beta-dexamethasone derivative (dexamethasone gel). Deoxycorticosterone gel was highly specific, since it retained mineralocorticoid but not glucocorticoid receptors, and dexamethasone gel exhibited high selectivity for glucocorticoid receptors since it did not bind mineralocorticoid receptors. The use of these two matrices allowed separation of mineralocorticoid and glucocorticoid receptors and further characterization of each type of cytosolic receptors after its isolation. Cytosolic mineralocorticoid and glucocorticoid receptors stabilized by tungstate were found to have a Stokes radius of approximately 6 nm, as determined by high performance size exclusion chromatography and a sedimentation coefficient of approximately 9 S, determined on a glycerol density gradient containing tungstate, under either high or low salt conditions. The hydrodynamic parameters, binding characteristics, and specificity of mineralocorticoid receptors were the same in the untreated and dexamethasone gel-treated cytosol. Similarly glucocorticoid receptor characteristics remained unchanged after deoxycorticosterone gel treatment, indicating biochemical independence of cytosolic mineralocorticoid and glucocorticoid receptors. The [3H]aldosterone receptor complex eluted from deoxycorticosterone gel was recovered with a 30-40% yield and a purification factor of about 1000. Purified mineralocorticoid receptors had the same sedimentation coefficient as cytosolic mineralocorticoid receptors (9 S) but a different Stokes radius (4 versus 6 nm). The decrease in the Stokes radius of the purified mineralocorticoid receptors was probably due to the gel filtration method. These results indicate that the newly synthesized matrix specific for mineralocorticoid receptors constitutes a powerful tool for their extensive purification.     

Effects on tissue and electrolytes of a mineralocorticoid blocker during DOCA-induced potassium depletion.

Chronic experiments were carried out on three groups of rats to evaluate tissue and electrolyte effects of a mineralocorticoid blocker canrenoate potassium (SC-14266) during DOCA-induced hypokalemic metabolic alkalosis. Group I animals received DOCA alone, group II received DOCA plus canrenoate, while group III received canrenoate alone. The daily dose ratio (per kilogram of body weight) was 180 mg canrenoate-0.45 mg DOCA. All animals ate a synthetic diet and drank 0.15 N NaHCO3. Group II animals demonstrated a lesser degree of metabolic alkalosis and a higher muscle potassium content when compared with group I rats. The most conspicuous histological abnormality was myocardial necrosis, the degree and extent of which was impressively reduced by the blocking agent.     

Gain of function mutation in the mineralocorticoid receptor of the Brown Norway rat

The aim of this research was to identify the molecular bases of differences in sensitivity to corticosteroid hormones between Brown Norway and Fischer 344 rats. We previously showed an apparent insensitivity to adrenalectomy in Brown Norway rats. Based on our first hypothesis of a different activity/reactivity of the mineralocorticoid signaling pathway between the two rat strains, we sequenced Brown Norway and Fischer 344 mineralocorticoid receptor cDNA and identified a tyrosine to cysteine substitution (Y73C) in the N-terminal part of the Brown Norway mineralocorticoid receptor. As a first step, this substitution gave us a means to distinguish the Brown Norway allele from the Fischer 344 at the mineralocorticoid receptor locus in an F2 population. We showed a strong genetic linkage between the mineralocorticoid receptor genotype and sensitivity to adrenalectomy. A subsequent genome-wide linkage analysis confirmed the involvement of the mineralocorticoid receptor locus and implicated other loci, including one on chromosome 4, which collectively explain a large part of the strain differences in corticosteroid receptor responses. In vitro studies further revealed that the Y73C substitution induces greater transactivation of the mineralocorticoid receptor by aldosterone, and surprisingly by progesterone as well, which could substitute for aldosterone after adrenalectomy in Brown Norway rats. We challenged this hypothesis in vivo and showed that plasma progesterone is higher in Brown Norway male rats and partially compensates for aldosterone after adrenalectomy. This work illustrates the interest of a pluristrategic approach to explore the mineralocorticoid receptor signaling pathway and its implication in the regulation of hydroelectrolytic homeostasis and blood pressure.     

Apparent mineralocorticoid excess, pseudohypoaldosteronism, and urinary electrolyte excretion: toward a redefinition of mineralocorticoid action

Patients with apparent mineralocorticoid excess (AME) have low or absent activity of the enzyme 11 beta OH steroid dehydrogenase (11SD), and inappropriately high intrarenal levels of cortisol resulting in Na+ retention and hypertension. Pseudohypoaldosteronism (PHA), in contrast, is characterized by salt wasting despite hyperaldosteronemia, reflecting low or absent mineralocorticoid receptors (MR). Although AME is presumed to reflect inappropriate cortisol occupancy of MR, several features also suggest inappropriate occupancy of glucocorticoid receptors (GR). To test this possibility, we administered carbenoxolone, which is known to block 11SD, to four patients with PHA, and observed marked mineralocorticoid effects, e.g., antinatriuresis and elevated plasma bicarbonate. To further test the possibility that occupancy of renal GR may induce a classical mineralocorticoid response, we administered the highly specific glucocorticoid RU 28362 to adrenalectomized rats and showed that it has profound antinatriuretic effects. Finally, by selectively blocking MR with RU 28318 or GR with RU 38486, we have shown that corticosterone, the physiologic glucocorticoid in rats, has an antinatriuretic effect in adrenalectomized rats via either MR or GR occupancy. Previous studies have clearly shown that MR are inherently nonselective and have equivalent intrinsic affinity for aldosterone, corticosterone, and cortisol. The present studies suggest that this nonselectivity includes the nuclear response element to which either MR or GR may bind to elicit a mineralocorticoid effect, and further underscore the importance of the enzyme 11SD in the specific mineralocorticoid action of aldosterone.     

Mineralocorticoid radioreceptor assay: application to adrenal-regeneration hypertension.

Identification of unknown hormones has traditionally involved utilizing a bioassay to initially detect the hormone and to follow its purification. However, radioreceptor assays may be more useful for this purpose by offering greater sensitivity and precision. A mineralocorticoid radioreceptor assay has been developed for use in conjunction with chromatographic separation of a urinary extract to detect the presence of unknown urinary mineralocorticoids. This assay utilizes competition of the unknown steroid and aldosterone for rat renal cytoplasmic mineralocorticoid receptors to enable mineralocorticoid quantitation in aldosterone equivalents. This assay provides 100 fold increase in sensitivity and a significant increase in precision over the commonly used adrenalectomized rat bioassay. The mineralocorticoid radioreceptor assay has been utilized to assay mineralocorticoid activity in chromatographic fractions of a urinary extract from rats with regenerating adrenals. A large area of mineralocorticoid radioreceptor activity has been identified which possibly represents an unknown mineralocorticoid contributing to the etiology of adrenal regeneration hypertension. This assay is applicable to other syndromes of postulated unknown mineralocorticoid excess, such as human low renin essential hypertension. In addition, similar radioreceptor assays are applicable for the initial detection of any type of hormone activity and for the subsequent purification and identification of this hormone.     

Steroid antagonism of the hypertensinogenic activity of adrenocortical steroids

Previous studies in sheep have provided evidence for a separate "hypertensinogenic" class of adrenocortical steroid activity which is not simply related to their classical mineralocorticoid (MC) and/or glucocorticoid (GC) actions. This study investigated the structure-activity relationships of the effects of structural analogues of prednisolone on mean arterial pressure (MAP), and MC and GC actions in sheep. Infusions of these synthetic GC at 0.6 and 24 mg/day produced variable pressor effects which were dissociated from their MC and GC actions. In other experiments, the minimum adrenocortical steroid requirement to reproduce the onset of ACTH-dependent hypertension was determined. Infusion of cortisol, aldosterone, 17 alpha-hydroxy progesterone and 17 alpha,20 alpha-dihydroxy-4-pregnene-3-one was found to be sufficient to reproduce the hypertensive response to ACTH administration in sheep. A subsequent experiment showed that substitution of cortisol by the more potent synthetic GC, prednisolone had no effect on MAP. Therefore, cortisol appears to exert an essential action in ACTH hypertension which is not dependent on its GC activity. Other studies have found that prednisolone (100 mg/day) antagonized 9 alpha-fluoro-prednisolone (0.6 mg/day) induced hypertension but not its MC effects. The effect of progesterone (500 mg/day) and the progesterone analogues, norethisterone, medroxy-progesterone and 16 alpha-methyl progesterone on ACTH (5 micrograms/kg per day) hypertension was investigated. Progesterone completely blocked the hypertension and MC effects of ACTH infusion, while medroxy-progesterone partially blocked the increase in MAP. These data support our concept of a "hypertensinogenic" class of steroid activity.