Mineralocorticoid Receptor mRNA Research Articles

Increased Expression of the Mineralocorticoid Receptor in the Brain of Spontaneously Hypertensive Rats

The mineralocorticoid receptor (MR) has been considered as both neuroprotective and damaging to the function of the central nervous system. MR may be also involved in central regulation of blood pressure. In the present study, we compared the expression of MR and the glucocorticoid receptor (GR) in the hippocampus and hypothalamus of 16-week-old spontaneously hypertensive rats (SHR) and normotensive control Wistar Kyoto (WKY) rats. In the hippocampus, MR expression was studied by in situ hybridization (ISH), quantitative polymerase chain reaction (PCR) and immunohistochemistry, whereas GR expression was analysed using the latter two procedures. Hypertensive animals showed an increased expression of MR mRNA in the whole hippocampus according to qPCR data and also in CA3 by ISH. Immunocytochemical staining for MR of the dorsal hippocampus, however, did not reveal differences between SHR and WKY rats. SHR showed elevated hypothalamic MR mRNA by qPCR, as well as an increased number of MR immunopositive cells in the magnocellular paraventricular region, compared to WKY rats. By contrast, expression levels of GR mRNA or protein in the hippocampus and hypothalamus of SHR were similar to those of WKY rats. Furthermore, we investigated the role of MR in the hypertensive rats by i.c.v. injection of the MR antagonist RU-2831. This compound produced a significant drop in blood pressure for SHR. In conclusion, MR expression is increased in the hippocampus and hypothalamus of SHR. We suggest that pathological MR overdrive may take responsibility for up-regulation of blood pressure and the encephalopathy of hypertension.

Neonatal exposure to low dose corticosterone persistently modulates hippocampal mineralocorticoid receptor expression and improves locomotor/exploratory behaviour in a mouse model of Rett syndrome

Rett syndrome (RTT) is a pervasive neurodevelopmental disorder, primarily affecting girls. RTT causes a wide variety of debilitating symptoms and no cure currently exists. Mouse models bearing mutations in the Mecp2 gene recapitulate most physiological and behavioural RTT-related abnormalities. Stimulating neonatal environments (e.g. brief maternal separations or maternal low-dose corticosterone supplementation) reduce stress and fear responses at adulthood. The present study investigated whether impacting early in development the hypothalamic-pituitary-adrenal axis, by exposing Mecp2-308 mutant pups to a low dose of corticosterone (50 µg/ml, during the 1st week of life) may contrast RTT-related abnormalities in neuroendocrine regulation and behavioural adaptation at adulthood. In line with previous reports, when fully symptomatic, MeCP2-308 mice showed a reduction in the regular nocturnal hyperactivity in the home-cage and increased anxiety-like behaviours and plasma corticosterone (CORT) levels in response to restraint stress. An abnormal elevation in mRNA levels of mineralocorticoid receptors (MR) and BDNF gene was also evident in the hippocampus of fully symptomatic mutant mice. Neonatal CORT modulated MR gene expression and behavioural reactivity towards a novel object, also restoring wt-like levels of locomotor/exploratory behaviour in mutant mice. Enhanced sensitivity to the neonatal treatment (in terms of increase in GR and MR mRNA levels), was also evident in the hippocampus of MeCP2-308 mice compared to wt littermates. Present results corroborate the hypothesis that targeting the glucocorticoid system may prove valid in contrasting at least some of the RTT-related symptoms and provide evidence that pharmacological interventions during critical early time windows can persistently improve the behavioural phenotype of RTT mice. Current data also support the emerging role played by Mecp2 in mediating the epigenetic programming induced by early life events and indicate that, in the absence of functional MeCP2, programming of the central nervous system in response to early environmental stimuli is abnormally regulated.This article is part of the Special Issue entitled ‘Neurodevelopmental Disorders’.

Corticosteroid-Dependent Plasticity Mediates Compulsive Alcohol Drinking in Rats

Alcoholism is characterized by a compulsion to seek and ingest alcohol, loss of control over intake, and the emergence of a negative emotional state during abstinence. We hypothesized that sustained activation of neuroendocrine stress systems (e.g., corticosteroid release via the hypothalamic-pituitary-adrenal axis) by alcohol intoxication and withdrawal and consequent alterations in glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation drive compulsive alcohol drinking. Our results showed that rats exposed to alcohol vapor to the point of dependence displayed increased alcohol intake, compulsive drinking measured by progressive-ratio responding, and persistent alcohol consumption despite punishment, assessed by adding quinine to the alcohol solution, compared with control rats that were not exposed to alcohol vapor. No group differences were observed in the self-administration of saccharin-sweetened water. Acute alcohol withdrawal was accompanied by downregulated GR mRNA in various stress/reward-related brain regions [i.e., prefrontal cortex, nucleus accumbens (NAc), and bed nucleus of the stria terminalis (BNST)], whereas protracted alcohol abstinence was accompanied by upregulated GR mRNA in the NAc core, ventral BNST, and central nucleus of the amygdala. No significant alterations in MR mRNA levels were found. Chronic GR antagonism with mifepristone (RU38486) prevented the escalation of alcohol intake and compulsive responding induced by chronic, intermittent alcohol vapor exposure. Chronic treatment with mifepristone also blocked escalated alcohol drinking and compulsive responding during protracted abstinence. Thus, the GR system appears to be involved in the development of alcohol dependence and may represent a potential pharmacological target for the treatment of alcoholism.

Transgenerational Effects of Prenatal Synthetic Glucocorticoids on Hypothalamic-Pituitary-Adrenal Function

Approximately 10% of pregnant women are at risk of preterm delivery and receive synthetic glucocorticoids (sGC) to promote fetal lung development. Studies have indicated that prenatal sGC therapy modifies hypothalamic-pituitary-adrenal (HPA) function in first-generation (F1) offspring. The objective of this study was to determine whether differences in HPA function and behavior are evident in the subsequent (F2) generation. Pregnant guinea pigs (F0) received betamethasone (BETA; 1 mg/kg) or saline on gestational d 40/41, 50/51, and 60/61. F1 females were mated with control males to create F2 offspring. HPA function was assessed in juvenile and adult F2 offspring. Locomotor activity was assessed in juvenile offspring. Analysis of HPA-related gene expression was undertaken in adult hippocampi, hypothalami, and pituitaries. Locomotor activity was reduced in F2 BETA males (P < 0.05). F2 BETA offspring displayed blunted cortisol response to swim stress (P < 0.05). After dexamethasone challenge, F2 BETA males and females displayed increased and decreased negative feedback, respectively. F2 BETA females had reduced pituitary levels of proopiomelanocortin (and adrenocorticotropic hormone), and corticotropin-releasing hormone receptor mRNA and protein (P < 0.05). F2 BETA males displayed increased hippocampal glucocorticoid receptor (P < 0.001), whereas in BETA females, hippocampal glucocorticoid receptor and mineralocorticoid receptor mRNA were decreased (P < 0.05). In conclusion, prenatal BETA treatment affects HPA function and behavior in F2 offspring. In F2 BETA females, pituitary function appears to be primarily affected, whereas hippocampal glucocorticoid feedback systems appear altered in both F2 BETA males and females. These data have clinical implication given the widespread use of repeat course glucocorticoid therapy in the management of preterm labour.

The Protective Side of the Mineralocorticoid Receptor

The Protective Side of the Mineralocorticoid Receptor

EDCs-induced glucocorticoid receptor related genes expression of the river pufferfish,Takifugu obscurus

Endocrine disrupting chemicals (EDCs) are of substantial concern when contaminating waters. We studied gene expression of larvae from river pufferfish, Takifugu obscurus exposed to EDCs. We cloned the full- or partial-length cDNA sequence of genes related to the cortisol pathway, such as the glucocorticoid receptor (GR), mineralocorticoid receptor (MR), heat shock protein (HSP) 70 and 90, phosphoenolpyruvate carboxykinase (PEPCK) and the FK506-binding protein 4 (FKBP52). The tissue and time-dependent expression of mRNA was studied by real-time PCR in T. obscurus exposed to two representative EDCs (bisphenol-A and 4-tert-octylphenol). HSP70, HSP90, MR and FKBP52 mRNA expression level was much higher than GR and PEPCK expression. GR mRNA expression level was significantly upregulated after 48 h in both EDC-treated fish groups compared with the control. Both groups also showed down-regulation patterns after 48 h. The initial expression of PEPCK in both groups was down-regulated after 24 h. In the bisphenol-A treated group, the expression of FKBP52 showed substantially high up-regulation from 6 to 48 h after exposure, and then strikingly reduced its expression level at 72 h. Our results provide insights into the EDCs metabolizing system of T. obscurus and offers baseline information for further research related to the possible use as a bio-indicator of this commercially important aquaculture fish species.

Differential physiological and endocrine responses of rainbow trout, Oncorhynchus mykiss, transferred from fresh water to ion-poor or salt water

To understand the physiological and molecular endocrine changes that occur in response to a salinity challenge, we transferred rainbow trout from fresh water to an ion-poor or 24‰ saltwater treatment for 14 days. An increase in gill Na +, K +-ATPase (NKA) activity in salt water was associated with higher mRNA expression for the NKA α1b subunit. In contrast, there was little change in gill NKA activity following transfer to ion-poor water, but the mRNA expression of NKA α1a was significantly elevated. Endocrine signals were assessed by measuring plasma cortisol concentrations and by quantifying changes in mRNA extracted from the gill for glucocorticoid receptors 1 and 2 (GR1 and GR2), mineralocorticoid receptor (MR), growth hormone receptor (GHR1), and prolactin receptor (PrlR). Cortisol increased after transfer to ion-poor and salt water, but both GR and MR mRNA in the gill showed little change. PrlR mRNA was significantly higher when fish were transferred to the ion-poor water and GHR1 mRNA was elevated during the saltwater challenge. This study demonstrated an increase in gill PrlR mRNA that parallels the changes in gill NKA α1a when rainbow trout were transferred to a lower salinity level. Furthermore, the increase in gill GHR1 mRNA supports the importance of GH for seawater acclimation as there is a corresponding increase in the expression of gill NKA α1b, the saltwater isoform. GH and Prl, therefore, may differentially determine the function of cortisol in both fresh- and saltwater ionoregulation.

Protective effects of mineralocorticoid receptor blockade against neuropathy in experimental diabetic rats

Mineralocorticoid receptor (MR) blockade is an effective treatment for hypertension and diabetic nephropathy. There are no data on the effects of MR blockade on diabetic peripheral neuropathy (DPN). The aim of this study was to determine whether MRs are present in the peripheral nerves and to investigate the effectiveness of MR blockade on DPN in streptozotocin (STZ)-induced diabetic rats. Expression of MR protein and messenger RNA (mRNA) was examined in the peripheral nerves using Western blot analysis and RT-PCR. We next studied the effects of the selective MR antagonist eplerenone and the angiotensin II receptor blocker candesartan on motor and sensory nerve conduction velocity (NCV), morphometric changes and cyclooxygenase-2 (COX-2) gene and NF-κB protein expression in the peripheral nerves of STZ-induced diabetic rats. Expression of MR protein and mRNA in peripheral nerves was equal to that in the kidney. Motor NCV was significantly improved by 8 weeks of treatment with either eplerenone (39.1 ± 1.2 m/s) or candesartan (46.4 ± 6.8 m/s) compared with control diabetic rats (33.7 ± 2.0 m/s) (p < 0.05). Sensory NCV was also improved by treatment with candesartan or eplerenone in diabetic rats. Eplerenone and candesartan caused significant improvement in mean myelin fibre area and mean myelin area compared with control diabetic rats (p < 0.05). COX-2 mRNA and NF-κB protein were significantly elevated in the peripheral nerves of diabetic rats compared with control rats, and treatment with eplerenone or candesartan reduced these changes in gene expression (p < 0.05). MR blockade may have neuroprotective effects on DPN.

Maternal Undernutrition Programs Offspring Adrenal Expression of Steroidogenic Enzymes

The aim of this study was to determine the influence of maternal undernutrition (MUN) on maternal and offspring adrenal steroidogenic enzymes. Pregnant Sprague-Dawley rats were 50% food-restricted from day 10 of gestation until delivery. Control animals received ad libitum food. Offspring were killed on day 1 of life (P1) and at 9 months. We determined the messenger RNA (mRNA) expression of steroidogenic enzymes by real-time reverse transcriptase polymerized chain reaction (RT-PCR). Maternal undernutrition inhibited maternal adrenal expression of P450 cholesterol side-chain cleavage enzyme (CYP11A1), 11 beta-hydroxylase (CYP11B1), aldosterone synthase (CYP11B2), and adrenocorticotropic hormone (ACTH) receptor (ACTH-R; MC2 gene) compared with control offspring. There was a marked downregulation in the expression of CYP11B1, CYP11B2, 11 β-hydroxysteroid dehydrogenase type 1 and 2 (HSD1 and HSD2), CYP11A1, ACTH receptor, steroidogenic acute regulatory protein (STAR), and mineralocorticoid receptor (MCR; NR3C2 gene) mRNA in P1 MUN offspring (both genders), with no changes in glucocorticoid receptor (GCR). Quantitative immunohistochemical analysis confirmed the PCR data for GCR and MCR in P1 offspring and demonstrated lower expression of leptin receptor protein (Ob-Ra/Ob-Rb) and mRNA in P1 MUN offspring. In 9-month adult male MUN offspring, the expression of HSD1, CYP11A1, CYP11B2, Ob-Ra/Ob-Rb, and GCR mRNA were significantly upregulated with a trend toward an increase in ACTH-R and a decrease in 17 alpha-hydroxylase (CYP17A1) expression. In adult female MUN offspring, similar to males, the expression of CYP11A1, ACTH-R, and Ob-Rb mRNA were increased, whereas GCR and CYP17A1 mRNA were decreased. These results indicate that the adrenal gland is a target of nutritional programming. In utero undernutrition has a global suppressive effect on maternal and P1 offspring adrenal steroidogenic enzymes in association with reduced circulating corticosterone levels in P1 offspring, which may be secondary to a negative feedback from elevated maternal GC levels and or leptin levels in MUN dams. Gender-specific differences in steroidogenic enzyme expression were found in adult MUN offspring. The common finding of increased ACTH receptor expression in MUN adults of both genders suggests an increased sensitivity of these offspring to stress.

Abnormal Glucocorticoid Receptor mRNA and Protein Isoform Expression in the Prefrontal Cortex in Psychiatric Illness

Stress has been implicated in the onset and illness course of schizophrenia and bipolar disorder. The effects of stress in these disorders may be mediated by abnormalities of the hypothalamic-pituitary-adrenal axis, and its corticosteroid receptors. We investigated mRNA expression of the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), and protein expression of multiple GRα isoforms, in the prefrontal cortex of 37 schizophrenia cases and 37 matched controls. Quantitative real-time PCR, western blotting, and luciferase assays were employed. In multiple regression analysis, schizophrenia diagnosis was a significant predictor of total GR mRNA expression (p<0.05), which was decreased (11.4%) in schizophrenia cases relative to controls. No significant effect of diagnosis on MR mRNA was detected. At the protein level, no significant predictors of total GRα protein or the full-length GRα isoform were identified. However, schizophrenia diagnosis was a strong predictor (p<0.0005) of the abundance of a truncated ≈ 50 kDa GRα protein isoform, putative GRα-D1, which was increased in schizophrenia cases (80.4%) relative to controls. This finding was replicated in a second cohort of 35 schizophrenia cases, 34 bipolar disorder cases, and 35 controls, in which both schizophrenia and bipolar disorder diagnoses were significant predictors of putative GRα-D1 abundance (p<0.05 and p=0.005, respectively). Full-length GRα was increased in bipolar disorder relative to schizophrenia cases. Luciferase assays demonstrated that the GRα-D1 isoform can activate transcription at glucocorticoid response elements. These findings confirm total GR mRNA reductions in schizophrenia and provide the first evidence of GR protein isoform abnormalities in schizophrenia and bipolar disorder.

Corticosteroids stimulate the amphibious behavior in mudskipper: Potential role of mineralocorticoid receptors in teleost fish

It has long been held that cortisol, a glucocorticoid in many vertebrates, carries out both glucocorticoid and mineralocorticoid actions in teleost fish. However, 11-deoxycorticosterone (DOC) has been identified as a specific endogenous ligand for the teleostean mineralocorticoid receptor (MR). Furthermore, the expressions of MR mRNA are modest in the osmoregulatory organs, but considerably higher in the brain of most teleosts. These recent findings suggest that the mineralocorticoid system (DOC/MR) may carry out some behavioral functions in fish. To test this possibility, we examined the effects of cortisol and DOC administration in the amphibious behavior in mudskipper (Periophthalmus modestus) in vivo. It was found that mudskippers remained in the water for an increased period of time when they were immersed into 5μM DOC or cortisol for 8h. Additionally, an exposure to 25μM DOC for 4 to 8h caused a decreased migratory frequency of mudskippers to the water, reflected a tendency to remain in the water. It was further observed that after 8h of intracerebroventricular (ICV) injection with 0.3pmol DOC or cortisol the staying period in the water increased in fish. The migratory frequency was decreased after ICV DOC injection which indicated that fishes stayed in the water. Concurrent ICV injections of cortisol with RU486 [a specific glucocorticoid-receptor (GR) antagonist] inhibited only the partial effects of cortisol. Together with no changes in the plasma DOC concentrations under terrestrial conditions, these results indicate the involvement of brain MRs as cortisol receptors in the preference for an aquatic habitat of mudskippers. Although the role of GR signaling cannot be excluded in the aquatic preference, our data further suggest that the MR may play an important role in the brain dependent behaviors of teleost fish.

Effects of ginsenosides on hypothalamic-pituitary-adrenal function and brain-derived neurotrophic factor in rats exposed to chronic unpredictable mild stress

Gingseng is commonly used in traditional Chinese medicine community for the treatment of depression-like disorders. Ginsenosides is considered to be the major active components of ginseng. Previous studies have demonstrated that ginsenosides produced antidepressant-like action in various mouse models of behavioral despair. The present study aimed to examine whether ginsenosides could affect the chronic unpredictable mild stress (CUMS)-induced depression in rats. The mechanism(s) underlying the antidepressant-like action was investigated by measuring serum corticosterone level, glucocorticoid receptor (GR), mineralocorticoid receptor (MR) and brain-derived neurotrophic factor (BDNF) mRNA levels in brain tissues. CUMS, being lasted for 6 weeks, caused depression-like behavior in rats, as indicated by the significant decrease in sucrose consumption and increase in immobility time in the forced swim test. Whereas serum corticosterone level was significantly increased in rats exposed to CUMS, expressions of GR mRNA in hippocampus, and BDNF mRNA in hippocampus and frontal cortex, were decreased in CUMS-treated rats. Daily intragastric administration of ginsenosides (12.5, 25, 50 mg x kg(-1)) during the six weeks of CUMS significantly suppressed behavioral and biochemical changes induced by CUMS. However, there was no significant difference in MR mRNA level among groups. The results suggest that the antidepressant-like action of ginsenosides is likely mediated by modulating the function of hypothalamic- pituitary -adrenal axis and increasing the expression of BDNF in brain tissues.

Age‐related changes in corticosteroid receptor expression and monoamine neurotransmitter concentrations in various brain regions of postnatal pigs

Negative early life experience may be associated with altered functioning of stress-related systems and may increase vulnerability to diseases later in life. Corticosteroids are important mediators of homeostasis and stress and exert their effects via two receptors, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR), and through the glucocorticoid-metabolizing enzymes 11β-hydroxysteroid dehydrogenase (11β-HSD) types 1 and 2 in a brain-region-specific manner. However, relatively little is known about the postnatal ontogeny of these receptors and enzymes in the central nervous system. Here we describe, for the first time, the postnatal ontogeny of central GR, MR, 11β-HSD1, and 11β-HSD2 gene expression and monoamine levels in stress-related brain regions of domestic pigs at 7, 21, and 35 days of age. During the postnatal period, there was an increase in GR, MR, and 11β-HSD1 mRNA expression in the pituitary and prefrontal cortex and an increase in MR mRNA expression in the hippocampus. We also demonstrated age-dependent changes in levels of noradrenaline and dopamine and their metabolites in the locus coeruleus, with the highest concentrations on day 7 compared with days 21 and 35. In conclusion, the dynamic changes in corticosteroid receptors and monoamines during neural development of postnatal pigs may represent periods of sensitivity to environmental stress that are comparable to some extent with those that are observed in primates and humans. Thus, these findings support the use of the domestic pig as an alternative animal model for humans in stress research.

11β-Hydroxysteroid Dehydrogenase Type 1 Deficiency Prevents Memory Deficits with Aging by Switching from Glucocorticoid Receptor to Mineralocorticoid Receptor-Mediated Cognitive Control

Local brain amplification of glucocorticoids (GCs) by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) plays a pivotal role in age-related memory deficits. 11β-HSD1 deficient mice are protected from spatial memory impairments with aging, but the underlying mechanisms are unknown. To determine which brain receptors [high-affinity mineralocorticoid receptors (MRs) or low-affinity glucocorticoid receptors (GRs)] are involved, spatial memory was measured in aged 11β-HSD1(-/-) mice before and during intracerebroventricular infusion (10 d) of spironolactone (MR antagonist) or RU486 (GR antagonist). Aged C57BL/6J control mice showed impaired spatial memory in the Y-maze; this improved with GR blockade, while MR blockade had no effect. In contrast, aged 11β-HSD1(-/-) mice showed intact spatial memory that became impaired with MR blockade, but not GR blockade. Hippocampal MR and GR mRNA expression and plasma corticosterone levels were not significantly altered with spironolactone or RU486 in either genotype. These data support the notion that 11β-HSD1 deficiency in aging mice leads to lower intracellular GC concentrations in brain, particularly in the hippocampus, which activate predominantly MRs to enhance memory, while in aging C57BL/6J controls, the increased intracellular GCs saturate MRs and activate predominantly GRs, thus impairing memory, an effect reversed by GR blockade.

Inhibition of mineralocorticoid receptor is a renoprotective effect of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor pitavastatin

The mineralocorticoid receptor has been implicated in the pathogenesis of chronic cardiorenal disease. Statins improve renal remodeling and dysfunction in patients with proteinuric kidney diseases. We aimed to clarify the beneficial effects and mechanisms of action of statins in renal insufficiency. Dahl salt-sensitive rats fed a high-salt diet were treated from 12 to 20 weeks of age with vehicle, the reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin, the synthetic cathepsin inhibitor E64d, or a low or high dosage of pitavastatin (1 or 3 mg/kg daily). Rats fed a low-salt diet served as controls. Rats on the high-salt diet developed massive proteinuria and glomerulosclerosis; these changes were attenuated by both doses of pitavastatin. The amounts of mRNAs or proteins for mineralocorticoid receptor, angiotensin-converting enzyme, angiotensin II type 1 receptor (AT1R), monocyte chemoattractant protein-1, osteopontin, macrophage infiltration, and NADPH subunits (gp91phox, p22phox, and Rac1) were significantly higher in the failing kidneys of vehicle-treated rats than in the kidneys of control rats. Either dose of pitavastatin significantly attenuated these changes. These effects of pitavastatin were mimicked by those of apocynin and E64d. Pretreatment with pitavastatin and apocynin inhibited mRNA and protein of mineralocorticoid receptor induced by angiotensin II in cultured podocytes. The beneficial effects of pitavastatin are likely attributable, at least in part, to attenuation of the mineralocorticoid receptor-dependent inflammatory mediator, matrix protein, and cathepsin expressions induced by AT1R-mediated NADPH oxidase activation in the kidneys of a salt-induced hypertensive Dahl salt-sensitive rat model.

Implication of the mineralocorticoid axis in rainbow trout osmoregulation during salinity acclimation

Cortisol and glucocorticoid receptors (GRs) play an important role in fish osmoregulation, whereas the involvement of the mineralocorticoid receptor (MR) and its putative ligand 11-deoxycorticosterone (DOC) is poorly investigated. In this study, we assessed the implication of DOC and MR in rainbow trout (Oncorhynchus mykiss) osmoregulation during hypo- and hypersaline acclimation in parallel with the cortisol-GR system. A RIA for DOC was developed to measure plasma DOC levels, and a MR-specific antibody was developed to localize MR protein in the gill, intestine, and kidney. This is the first study to report DOC plasma levels during salinity change and MR localization in fish osmoregulatory tissue. Corticosteroid receptor mRNA abundance was investigated in osmoregulatory tissue during salinity acclimation, and the effect of cortisol and DOC on ionic transporters gene expression was assayed using an in vitro gill incubation method. Differential tissue-, salinity-, and time-dependent changes in MR mRNA levels during both hyper- and hyposaline acclimations and the ubiquitous localization of MR in osmoregulatory tissue suggest a role for the MR in osmoregulation. Presumably, DOC does not act as ligand for MR in osmoregulation because there were no changes in plasma DOC levels during either freshwater-seawater (FW-SW) or SW-FW acclimation or any effect of DOC on gill ionic transporter mRNA levels in the gill. Taken together, these results suggest a role for MR, but not for DOC, in osmoregulation and confirm the importance of cortisol as a major endocrine regulator of trout osmoregulation.

Prenatal overexposure to glucocorticoids programs renal 11β-hydroxysteroid dehydrogenase type 2 expression and salt-sensitive hypertension in the rat

Prenatal glucocorticoid excess programs hypertension in adulthood. The underlying mechanisms are unknown. Here, we tested whether hypertension in this model is due to increased renal mineralocorticoid activity. Pregnant rats were injected daily with the synthetic glucocorticoid dexamethasone (DEX) or vehicle during the last week of pregnancy. Blood pressure, electrolytes and target gene expression were measured in the offspring. Adult DEX-treated offspring were hypertensive (SBP, 140.1 ± 2.4 vs. 128.6 ± 3.2 mmHg; P = 0.009), hypokalemic (4.5 ± 0.2 vs. 5.1 ± 0.2 mmol/l; P = 0.03) and had suppressed plasma renin concentration (23.6 ± 4.8 vs. 43.8 ± 5.9 ng/ml; P = 0.017). DEX programming had similar effects in younger rats (age 2 months), but only when fed a high-salt diet. Although these data are consistent with excess mineralocorticoid activity, plasma aldosterone levels were unaffected and daily urinary aldosterone values were decreased (136.1 ± 27.0 vs. 303.6 ± 47.0 ng/kg; P = 0.008). Accordingly, we assessed renal factors that might influence mineralocorticoid responsiveness. Renal expression of mineralocorticoid receptor and glucocorticoid receptor mRNAs was unaltered, as was 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) which regenerates active glucocorticoids. However, renal mRNA for 11β-HSD2, which catalyses inactivation of glucocorticoids in the distal nephron and thus protects mineralocorticoids from glucocorticoids, was decreased by 45% in both new born and adult rats (P < 0.01). The functional significance of this reduction was confirmed by measurements of renal 11β-HSD activity and by demonstrating that the mineralocorticoid properties of cortisol were enhanced in DEX-programmed rats. Additionally, the difference in blood pressure between DEX and control groups was abolished upon administration of spironolactone, a mineralocorticoid receptor antagonist. The blood pressure phenotype of DEX-programmed rats may in part be explained by a life-long reduction in renal 11β-HSD2 activity. Salt-sensitive hypertension could be programmed by prenatal stress.

Decreased expression of mineralocorticoid receptor mRNA and its splice variants in postmortem brain regions of patients with major depressive disorder

Appropriate signaling in the brain by the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) is critical in regulation of the hypothalamic–pituitary–adrenal (HPA) axis, emotional arousal and cognitive performance. To date, few data exist on MR (and GR) expression in the brain of patients suffering from major depressive disorder (MDD). With the help of quantitative PCR we assessed MR and GR mRNA expression, including the splice variants MRα and MRβ, in tissue samples from the hippocampus, amygdala, inferior frontal gyrus, cingulate gyrus and nucleus accumbens. Expression levels were compared between tissue samples from six MDD patients and six non-depressed subjects. Relative to total GR, total MR mRNA expression was higher in hippocampus and lower in the amygdala, inferior frontal gyrus and nucleus accumbens. Both MRα and MRβ could be detected in all brain regions that were analyzed, although MRβ expression was low. Significantly lower expression levels (30–50%) were detected for MR or GR in hippocampal, inferior frontal gyrus and cingulate gyrus tissue from MDD patients ( p < .05), while no differences were found in the amygdala or nucleus accumbens. The data show that both MRα and MRβ mRNA are expressed throughout the human limbic brain with highest expressions in the hippocampus. A decreased expression of corticosteroid receptors in specific brain regions of MDD patients could underlie HPA hyperactivity, mood and cognitive disturbances often observed in patients suffering from stress-related psychopathologies.

Mineralocorticoid and glucocorticoid receptor mRNA expression in the brain of translocated chukar (Alectoris chukar)

Although translocation is an important conservation tool in the effort to create self-sustaining wild populations of threatened species, avian translocations have a high failure rate and causes for failure are poorly understood. While “stress” is considered to play a major role in translocation failure, the physiological changes associated with chronic stress resulting from translocation have been investigated only recently. Translocation results in chronic stress-induced alterations of stress response physiology in the chukar (Alectoris chukar) and in the present study we tested the hypothesis that changes in the hypothalamic–pituitary–adrenal axis (HPA) are correlated with changes in the brain, specifically at the level of the glucocorticoid and mineralocorticoid receptors (GR and MR, respectively) in the hippocampus and hypothalamus. Our previous research has shown that there are apparent changes in GR and MR expression in the brain of experimentally chronically stressed European starlings (Sturnus vulgaris). In the present study however, translocation had no major detectable effect on levels of GR or MR mRNA expression in the hippocampus or hypothalamus of wild chukar suggesting that the observed dysregulation of the HPA axis by translocation may not be a result of such upstream changes.

Mineralocorticoid receptor, CYP11B2 mRNA expression, and atrial matrix remodelling in patients with atrial fibrillation

Objective — Atrial fibrillation is associated with the activation of the renin-angiotensin-aldosterone system in the atria. It is not clear whether the expression of mineralocorticoid receptor (MR) and aldosterone synthase CYP11B2 in patients with atrial fibrillation is altered. This study aimed to investigate the mRNA expression of MR and CYP11B2 and to reveal the correlation between CYP11B2 mRNA and matrix remodelling in patients with atrial fibrillation.Methods — Twenty-five patients with rheumatic heart valve disease, 12 in sinus rhythm and 13 in atrial fibrillation (> 6 months), underwent a valve replacement operation and right and left atrial lateral wall tissue samples were obtained. The MR and CYP11B2 expressions were analysed at the mRNA level and collagen volume fraction was determined by Van Gieson’s staining.Results — Collagen volume fraction was found to be increased significantly in atrial fibrillation groups compared with sinus rhythm groups (P< 0.001). Both the mRNA of MR and CYP11B2 were significantly increased in the fibrillation group compared with the group in sinus rhythm (P< 0.01). Collagen volume fraction significantly and positively correlated with left atrial dimension (r= 0.845, P< 0.001).There was a positive correlation between CYP11B2 mRNA and collagen volume fraction (r= 0.757, P< 0.001).Conclusion — Increased expression of MR and CYP11B2 in the atria is one of the molecular mechanisms for the development of atrial interstitial fibrosis in patients with atrial fibrillation.