11beta-hydroxysteroid dehydrogenase type 2 activity in hypothalamic paraventricular nucleus modulates sympathetic excitation

Glycyrrhizic acid induced acquired apparent mineralocorticoid excess syndrome with a hyperadrenergic state: a case report

BACKGROUND

Syndrome of apparent mineralocorticoid excess (AME) is characterized by excessive MR stimulation despite low levels of aldosterone. 11Beta-hydroxysteroid dehydrogenase-2 (11βDSH-2) inactivates cortisol to cortisone, preventing cortisol-induced MR activation. Genetic defects in 11βDSH-2 cause AME through accumulation of cortisol in the distal nephron, leading to MR activation induced hypertension, hypokalemia and metabolic alkalosis. Acquired AME can occur due to the ingestion of glycyrrhizic acid, found in licorice root, which inhibits 11βDSH-2 and has additional effects on cortisol homeostasis through inhibition of 11βDSH-1.

CASE REPORT

We present a case of acquired AME with a hyperadrenergic symptoms induced by ingestion of Advanced Liver Support, a nutritional supplement produced by Advanced BioNutritionals(R), in a 65-year-old Caucasian female who presented with accelerated hypertension, hypokalemia, metabolic alkalosis and adrenergic symptoms. Cessation of the licorice-containing supplement resulted in complete resolution of the patient's hypertension, symptoms and abnormal lab values. To our knowledge this is the first reported case of AME from this supplement, and the first to describe accompanying hyperadrenergic symptoms.

CONCLUSIONS

Glycyrrhizic acid is increasingly being found in unregulated nutritional supplements and has the potential to induce a reversable syndrome of AME. Acquired AME should be suspected in individuals who present with hypertension along with hypokalemia, metabolic alkalosis and low plasma renin and serum aldosterone levels.

Intrauterine developmental origin, programming mechanism, and prevention strategy of fetal-originated hypercholesterolemia

There is increasing evidence that hypercholesterolemia has an intrauterine developmental origin. However, the pathogenesis of fetal-originated is still lacking in a theoretical system, which makes its clinical early prevention and treatment difficult. It has been found that an adverse environment during pregnancy (e.g., xenobiotic exposure) may lead to changes in fetal blood cholesterol levels through changing maternal cholesterol metabolic function and/or placental cholesterol transport function and may also directly affect the liver cholesterol metabolic function of the offspring in utero and continue after birth. Adverse environmental conditions during pregnancy may also raise maternal glucocorticoid levels and promote the placental glucocorticoid barrier opening, leading to fetal overexposure to maternal glucocorticoids. Intrauterine high-glucocorticoid exposure can alter the liver cholesterol metabolism of offspring, resulting in an increased susceptibility to hypercholesterolemia after birth. Abnormal epigenetic modifications are involved in the intrauterine programming mechanism of fetal-originated hypercholesterolemia. Some interventions targeted at pregnant mothers or offspring in early life have been proposed to effectively prevent and treat the development of fetal-originated hypercholesterolemia. In this paper, the recent research progress on fetal-originated hypercholesterolemia was reviewed, with emphasis on intrauterine maternal glucocorticoid programming mechanisms, in order to provide a theoretical basis for its early clinical warning, prevention, and treatment.

Mechanisms of Post-critical Illness Cardiovascular Disease

Prolonged critical care stays commonly follow trauma, severe burn injury, sepsis, ARDS, and complications of major surgery. Although patients leave critical care following homeostatic recovery, significant additional diseases affect these patients during and beyond the convalescent phase. New cardiovascular and renal disease is commonly seen and roughly one third of all deaths in the year following discharge from critical care may come from this cluster of diseases. During prolonged critical care stays, the immunometabolic, inflammatory and neurohumoral response to severe illness in conjunction with resuscitative treatments primes the immune system and parenchymal tissues to develop a long-lived pro-inflammatory and immunosenescent state. This state is perpetuated by persistent Toll-like receptor signaling, free radical mediated isolevuglandin protein adduct formation and presentation by antigen presenting cells, abnormal circulating HDL and LDL isoforms, redox and metabolite mediated epigenetic reprogramming of the innate immune arm (trained immunity), and the development of immunosenescence through T-cell exhaustion/anergy through epigenetic modification of the T-cell genome. Under this state, tissue remodeling in the vascular, cardiac, and renal parenchymal beds occurs through the activation of pro-fibrotic cellular signaling pathways, causing vascular dysfunction and atherosclerosis, adverse cardiac remodeling and dysfunction, and proteinuria and accelerated chronic kidney disease.

11β-hydroxysteroid dehydrogenases: A growing multi-tasking family

This review briefly addresses the history of the discovery and elucidation of the three cloned 11β-hydroxysteroid dehydrogenase (11βHSD) enzymes in the human, 11βHSD1, 11βHSD2 and 11βHSD3, an NADP⁺-dependent dehydrogenase also called the 11βHSD1-like dehydrogenase (11βHSD1L), as well as evidence for yet identified 11βHSDs. Attention is devoted to more recently described aspects of this multi-functional family. The importance of 11βHSD substrates other than glucocorticoids including bile acids, 7-keto sterols, neurosteroids, and xenobiotics is discussed, along with examples of pathology when functions of these multi-tasking enzymes are disrupted. 11βHSDs modulate the intracellular concentration of glucocorticoids, thereby regulating the activation of the glucocorticoid and mineralocorticoid receptors, and 7β-27-hydroxycholesterol, an agonist of the retinoid-related orphan receptor gamma (RORγ). Key functions of this nuclear transcription factor include regulation of immune cell differentiation, cytokine production and inflammation at the cell level. 11βHSD1 expression and/or glucocorticoid reductase activity are inappropriately increased with age and in obesity and metabolic syndrome (MetS). Potential causes for disappointing results of the clinical trials of selective inhibitors of 11βHSD1 in the treatment of these disorders are discussed, as well as the potential for more targeted use of inhibitors of 11βHSD1 and 11βHSD2.

Aldosterone-sensitive HSD2 neurons in mice

Sodium deficiency elevates aldosterone, which in addition to epithelial tissues acts on the brain to promote dysphoric symptoms and salt intake. Aldosterone boosts the activity of neurons that express 11-beta-hydroxysteroid dehydrogenase type 2 (HSD2), a hallmark of aldosterone-sensitive cells. To better characterize these neurons, we combine immunolabeling and in situ hybridization with fate mapping and Cre-conditional axon tracing in mice. Many cells throughout the brain have a developmental history of Hsd11b2 expression, but in the adult brain one small brainstem region with a leaky blood-brain barrier contains HSD2 neurons. These neurons express Hsd11b2, Nr3c2 (mineralocorticoid receptor), Agtr1a (angiotensin receptor), Slc17a6 (vesicular glutamate transporter 2), Phox2b, and Nxph4; many also express Cartpt or Lmx1b. No HSD2 neurons express cholinergic, monoaminergic, or several other neuropeptidergic markers. Their axons project to the parabrachial complex (PB), where they intermingle with AgRP-immunoreactive axons to form dense terminal fields overlapping FoxP2 neurons in the central lateral subnucleus (PBcL) and pre-locus coeruleus (pLC). Their axons also extend to the forebrain, intermingling with AgRP- and CGRP-immunoreactive axons to form dense terminals surrounding GABAergic neurons in the ventrolateral bed nucleus of the stria terminalis (BSTvL). Sparse axons target the periaqueductal gray, ventral tegmental area, lateral hypothalamic area, paraventricular hypothalamic nucleus, and central nucleus of the amygdala. Dual retrograde tracing revealed that largely separate HSD2 neurons project to pLC/PB or BSTvL. This projection pattern raises the possibility that a subset of HSD2 neurons promotes the dysphoric, anorexic, and anhedonic symptoms of hyperaldosteronism via AgRP-inhibited relay neurons in PB.

Enteric Microbiota⁻Gut⁻Brain Axis from the Perspective of Nuclear Receptors

Nuclear receptors (NRs) play a key role in regulating virtually all body functions, thus maintaining a healthy operating body with all its complex systems. Recently, gut microbiota emerged as major factor contributing to the health of the whole organism. Enteric bacteria have multiple ways to influence their host and several of them involve communication with the brain. Mounting evidence of cooperation between gut flora and NRs is already available. However, the full potential of the microbiota interconnection with NRs remains to be uncovered. Herewith, we present the current state of knowledge on the multifaceted roles of NRs in the enteric microbiota–gut–brain axis.

Aldosterone infusion into the 4th ventricle produces sodium appetite with baroreflex attenuation independent of renal or blood pressure changes

Aldosterone infusion into the 4th ventricle (4th V), upstream the nucleus of the solitary tract (NTS), produces strong 0.3 M NaCl intake. In the present study, we investigated whether aldosterone infusion into the 4th V activates HSD2 neurons, changes renal excretion, or alters blood pressure and cardiovascular reflexes. Chronic infusion of aldosterone (100 ng/h) into the 4th V increased daily 0.3 M NaCl intake (up to 44 ± 10, vs. vehicle: 5.6 ± 3.4 ml/24 h) and also c-Fos expression in HSD2 neurons in the NTS and in non-HSD2 neurons in the NTS. Natriuresis, diuresis and positive sodium balance were present in rats that ingested 0.3 M NaCl, however, renal excretion was not modified by 4th V aldosterone in rats that had no access to NaCl. 4th V aldosterone also reduced baroreflex sensitivity (-2.8 ± 0.5, vs. vehicle: -5.1 ± 0.9 bpm/mmHg) in animals that had sodium available, without changing blood pressure. The results suggest that sodium intake induced by aldosterone infused into the 4th V is associated with activation of NTS neurons, among them the HSD2 neurons. Aldosterone infused into the 4th V in association with sodium intake also impairs baroreflex sensitivity, without changing arterial pressure.

Pro- versus Antinociceptive Nongenomic Effects of Neuronal Mineralocorticoid versus Glucocorticoid Receptors during Rat Hind Paw Inflammation

Background

In naive rats, corticosteroids activate neuronal membrane–bound glucocorticoid and mineralocorticoid receptors in spinal cord and periphery to modulate nociceptive behavior by nongenomic mechanisms. Here we investigated inflammation-induced changes in neuronal versus glial glucocorticoid and mineralocorticoid receptors and their ligand-mediated nongenomic impact on mechanical nociception in rats.

Methods

In Wistar rats (n = 5 to 7/group) with Freund’s complete adjuvant hind paw inflammation, we examined glucocorticoid and mineralocorticoid receptor expression in spinal cord and peripheral sensory neurons versus glial using quantitative reverse transcription-polymerase chain reaction (qRT-PCR), Western blot, immunohistochemistry, and radioligand binding. Moreover, we explored the expression of mineralocorticoid receptors protecting enzyme 11-betahydroxysteroid dehydrogenase type 2 as well as the nociceptive behavioral changes after glucocorticoid and mineralocorticoid receptors agonist or antagonist application.

Results

Hind paw inflammation resulted in significant upregulation of glucocorticoid receptors in nociceptive neurons of spinal cord (60%) and dorsal root ganglia (15%) as well as mineralocorticoid receptors, while corticosteroid plasma concentrations remained unchanged. Mineralocorticoid (83 ± 16 fmol/mg) but not glucocorticoid (104 ± 20 fmol/mg) membrane binding sites increased twofold in dorsal root ganglia concomitant with upregulated 11-betahydroxysteroid dehydrogenase type 2 (43%). Glucocorticoid and mineralocorticoid receptor expression in spinal microglia and astrocytes was small. Importantly, glucocorticoid receptor agonist dexamethasone or mineralocorticoid receptor antagonist canrenoate-K rapidly and dose-dependently attenuated nociceptive behavior. Isobolographic analysis of the combination of both drugs showed subadditive but not synergistic or additive effects.

Conclusions

The enhanced mechanical sensitivity of inflamed hind paws accompanied with corticosteroid receptor upregulation in spinal and peripheral sensory neurons was attenuated immediately after glucocorticoid receptor agonist and mineralocorticoid receptor antagonist administration, suggesting acute nongenomic effects consistent with detected membrane-bound corticosteroid receptors.

Update on angiotensin II: new endocrine connections between the brain, adrenal glands and the cardiovascular system

In the brain, angiotensinergic pathways play a major role in chronic regulation of cardiovascular and electrolyte homeostasis. Increases in plasma angiotensin II (Ang II), aldosterone, [Na⁺] and cytokines can directly activate these pathways. Chronically, these stimuli also activate a slow neuromodulatory pathway involving local aldosterone, mineralocorticoid receptors (MRs), epithelial sodium channels and endogenous ouabain (EO). This pathway increases AT₁R and NADPH oxidase subunits and maintains/further increases the activity of angiotensinergic pathways. These brain pathways not only increase the setpoint of sympathetic activity per se, but also enhance its effectiveness by increasing plasma EO and EO-dependent reprogramming of arterial and cardiac function. Blockade of any step in this slow pathway or of AT₁R prevents Ang II-, aldosterone- or salt and renal injury-induced forms of hypertension. MR/AT₁R activation in the CNS also contributes to the activation of sympathetic activity, the circulatory and cardiac RAAS and increase in circulating cytokines in HF post MI. Chronic central infusion of an aldosterone synthase inhibitor, MR blocker or AT₁R blocker prevents a major part of the structural remodeling of the heart and the decrease in LV function post MI, indicating that MR activation in the CNS post MI depends on aldosterone, locally produced in the CNS. Thus, Ang II, aldosterone and EO are not simply circulating hormones that act on the CNS but rather they are also paracrine neurohormones, locally produced in the CNS, that exert powerful effects in key CNS pathways involved in the long-term control of sympathetic and neuro-endocrine function and cardiovascular homeostasis.

Cell discharge correlates of posterior hypothalamic theta rhythm. Recipe for success in recording stable field potential

The theta rhythm discovered in the posterior hypothalamus area (PHa) differs from theta observed in the hippocampal formation. In comparison to hippocampal spontaneous theta, the theta recorded in the PHa is rarely registered, has lower amplitude, often disappears, and sometimes returns after a few minutes. These features indicate that spontaneous theta recorded in the PHa is not an appropriate experimental model to search for the correlation between PHa cell discharges and local field potential. In this paper we present standard experimental conditions necessary to record theta-related cells in the PHa in anesthetized rats. Three pharmacological agents were used in the experiments to induce PHa theta rhythm in urethanized rats: carbachol (CCH), carbenoxolone and kainic acid, which are potent enough to induce well-synchronized PHa theta. However, CCH was found to be the best pharmacological tool to induce PHa theta oscillations, due to its longest duration of action and lack of preliminary epileptogenic effects. It seems that CCH-induced theta can be the most suitable pharmacological model for experiments with the use of protocol of long-lasting recordings of PHa theta-related cell discharges.

Localisation of 11β-Hydroxysteroid Dehydrogenase Type 2 in Mineralocorticoid Receptor Expressing Magnocellular Neurosecretory Neurones of the Rat Supraoptic and Paraventricular Nuclei

An accumulating body of evidence suggests that the activity of the mineralocorticoid, aldosterone, in the brain via the mineralocorticoid receptor (MR) plays an important role in the regulation of blood pressure. MR was recently found in vasopressin and oxytocin synthesising magnocellular neurosecretory cells (MNCs) in both the paraventricular (PVN) and supraoptic (SON) nuclei in the hypothalamus. Considering the physiological effects of these hormones, MR in these neurones may be an important site mediating the action of aldosterone in blood pressure regulation within the brain. However, aldosterone activation of MR in the hypothalamus remains controversial as a result of the high binding affinity of glucocorticoids to MR at substantially higher concentrations compared to aldosterone. In aldosterone-sensitive epithelia, the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) prevents glucocorticoids from binding to MR by converting glucocorticoids into inactive metabolites. The present study aimed to determine whether 11β-HSD2, which increases aldosterone selectivity, is expressed in MNCs. Specific 11β-HSD2 immunoreactivity was found in the cytoplasm of the MNCs in both the SON and PVN. In addition, double-fluorescence confocal microscopy demonstrated that MR-immunoreactivity and 11β-HSD2-in situ hybridised products are colocalised in MNCs. Lastly, single-cell reverse transcriptase-polymerase chain reaction detected MR and 11β-HSD2 mRNAs from cDNA libraries derived from single identified MNCs. These findings strongly suggest that MNCs in the SON and PVN are aldosterone-sensitive neurones.

Brain mineralocorticoid receptors in cognition and cardiovascular homeostasis

Mineralocorticoid receptors (MR) mediate diverse functions supporting osmotic and hemodynamic homeostasis, response to injury and inflammation, and neuronal changes required for learning and memory. Inappropriate MR activation in kidneys, heart, vessels, and brain hemodynamic control centers results in cardiovascular and renal pathology and hypertension. MR binds aldosterone, cortisol and corticosterone with similar affinity, while the glucocorticoid receptor (GR) has less affinity for cortisol and corticosterone. As glucocorticoids are more abundant than aldosterone, aldosterone activates MR in cells co-expressing enzymes with 11β-hydroxydehydrogenase activity to inactivate them. MR and GR co-expressed in the same cell interact at the molecular and functional level and these functions may be complementary or opposing depending on the cell type. Thus the balance between MR and GR expression and activation is crucial for normal function. Where 11β-hydroxydehydrogenase 2 (11β-HSD2) that inactivates cortisol and corticosterone in aldosterone target cells of the kidney and nucleus tractus solitarius (NTS) is not expressed, as in most neurons, MR are activated at basal glucocorticoid concentrations, GR at stress concentrations. An exception may be pre-autonomic neurons of the PVN which express MR and 11β-HSD1 in the absence of hexose-6-phosphate dehydrogenase required to generate the requisite cofactor for reductase activity, thus it acts as a dehydrogenase. MR antagonists, valuable adjuncts to the treatment of cardiovascular disease, also inhibit MR in the brain that are crucial for memory formation and exacerbate detrimental effects of excessive GR activation on cognition and mood. 11β-HSD1 inhibitors combat metabolic and cognitive diseases related to glucocorticoid excess, but may exacerbate MR action where 11β-HSD1 acts as a dehydrogenase, while non-selective 11β-HSD1&2 inhibitors cause injurious disruption of MR hemodynamic control. MR functions in the brain are multifaceted and optimal MR:GR activity is crucial. Therefore selectively targeting down-stream effectors of MR specific actions may be a better therapeutic goal.

Actions of circulating angiotensin II and aldosterone in the brain contributing to hypertension

In the past 1-2 decades, it has become apparent that the brain renin-angiotensin-aldosterone system (RAAS) plays a crucial role in the regulation of blood pressure (BP) by the circulating RAAS. In the brain, angiotensinergic sympatho-excitatory pathways do not contribute to acute, second-to-second regulation but play a major role in the more chronic regulation of the setpoint for sympathetic tone and BP. Increases in plasma angiotensin II (Ang II) or aldosterone and in cerebrospinal fluid [Na(+)] can directly activate these pathways and chronically further activate/maintain enhanced activity by a slow neuromodulatory pathway involving local aldosterone, mineralocorticoid receptors (MRs), epithelial sodium channels, and endogenous ouabain. Blockade of any step in this slow pathway prevents Ang II-, aldosterone-, or salt and renal injury-induced forms of hypertension. It appears that the renal and arterial actions of circulating aldosterone and Ang II act as amplifiers but are not sufficient to cause chronic hypertension if their central actions are prevented, except perhaps at high concentrations. From a clinical perspective, oral treatment with an angiotensin type 1 (AT1)-receptor blocker at high doses can cause central AT1-receptor blockade and, in humans, lower sympathetic nerve activity. Low doses of the MR blocker spironolactone appear sufficient to cause central MR blockade and a decrease in sympathetic nerve activity. Integrating the brain actions of the circulating RAAS with its direct renal and arterial actions provides a better framework to understand the role of the circulating RAAS in the pathophysiology of hypertension and heart failure and to direct therapeutic strategies.

Aberrant Rac1-mineralocorticoid receptor pathways in salt-sensitive hypertension

According to Guyton's model, impaired renal sodium excretion plays a key role in the increased salt sensitivity of blood pressure (BP). Several factors contribute to impaired renal sodium excretion, including the sympathetic nervous system, the renin-angiotensin system and aldosterone. Accumulating evidence suggests that abnormalities in aldosterone and its receptor (i.e. the mineralocorticoid receptor (MR)) are involved in the development of salt-sensitive (SS) hypertension. Patients with metabolic syndrome often exhibit hyperaldosteronism and are susceptible to SS hypertension. Aldosterone secretion from the adrenal glands is not suppressed in obese hypertensive rats fed a high-salt diet because of the abundant production of adipocyte-derived aldosterone-releasing factors, which are independent of the negative feedback regulation of aldosterone secretion by the renin-angiotensin-aldosterone system. Increased plasma aldosterone levels lead to SS hypertension via MR activation in the kidney. Renal MR activity is increased in Dahl salt-sensitive rats fed a high-salt diet, despite the appropriate suppression of plasma aldosterone levels. In this rat strain, activation of MR in the distal nephron causes salt-induced hypertension. This paradoxical response of the MR to salt loading can be attributed to activation of Rac1, a small GTPase. In the presence of aldosterone, activated Rac1 synergistically and directly activates MR in a ligand-independent manner. Thus, Rac1 activation in the kidney determines the salt sensitivity of BP. Together, the available evidence suggests that the aberrant Rac1-MR pathway plays a key role in the development of SS hypertension.

The role of CNS in salt-sensitive hypertension

The role of sympathetic nerve activity in hypertension is currently receiving increased attention, because catheter-based renal denervation was recently shown to reduce blood pressure safely in patients with treatment-resistant hypertension. The central nervous system, which regulates sympathetic nerve activity and blood pressure, is pivotal. Central sympathoexcitation has been shown to be deeply involved in the pathogenesis of salt-sensitive hypertension, although its precise mechanisms have not yet been fully elucidated due to their complexity. Recently, a role for brain oxidative stress in sympathoexcitation has been suggested in some hypertensive animal models. We have demonstrated that increased brain oxidative stress may elevate arterial pressure through central sympathoexcitation in salt-sensitive hypertension. Several factors other than oxidative stress have also been shown to play important roles in central sympathetic activation. In the future, strategies may be developed to elicit a sympathetic inhibition by modulating these factors to prevent and manage salt-sensitive hypertension.

Expression of mineralocorticoid and glucocorticoid receptors in preautonomic neurons of the rat paraventricular nucleus

Activation of mineralocorticoid receptors (MR) of the hypothalamic paraventricular nucleus (PVN) increases sympathetic excitation. To determine whether MR and glucocorticoid receptors (GR) are expressed in preautonomic neurons of the PVN and how they relate to endogenous aldosterone levels in healthy rats, retrograde tracer was injected into the intermediolateral cell column at T4 to identify preautonomic neurons in the PVN. Expression of MR, GR, 11-β hydroxysteroid dehydrogenase1 and 2 (11β-HSD1, 2), and hexose-6-phosphate dehydrogenase (H6PD) required for 11β-HSD1 reductase activity was assessed by immunohistochemistry. RT-PCR and Western blot analysis were used to determine MR gene and protein expression. Most preautonomic neurons were in the caudal mediocellular region of PVN, and most expressed MR; none expressed GR. 11β-HSD1, but not 11β-HSD2 nor H6PD immunoreactivity, was detected in the PVN. In rats with chronic low or high sodium intakes, the low-sodium diet was associated with significantly higher plasma aldosterone, MR mRNA and protein expression, and c-Fos immunoreactivity within labeled preautonomic neurons. Plasma corticosterone and sodium and expression of tonicity-responsive enhancer binding protein in the PVN did not differ between groups, suggesting osmotic adaptation to the altered sodium intake. These results suggest that MR within preautonomic neurons in the PVN directly participate in the regulation of sympathetic nervous system drive, and aldosterone may be a relevant ligand for MR in preautonomic neurons of the PVN under physiological conditions. Dehydrogenase activity of 11β-HSD1 occurs in the absence of H6PD, which regenerates NADP(+) from NADPH and may increase MR gene expression under physiological conditions.

Corticosterone-activated mineralocorticoid receptor contributes to salt-induced sympathoexcitation in pressure overload mice

Abstract We previously reported that pressure overload (PO) activates the hypothalamic mineralocorticoid receptor (MR) and angiotensin II type 1 receptor (AT1R). Moreover, salt intake further activates the hypothalamic MR and AT1R, resulting in salt-induced sympathoexcitation. However, the mechanism underlying this pathway activation in response to a high salt intake remains unknown. Although the role of aldosterone is extensively examined as a ligand for MR, corticosterone is able to bind to MR. Therefore, we hypothesized that corticosterone contributes to salt-induced sympathoexcitation in PO-mice. Four weeks after aortic banding to produce PO-mice, or a sham operation for controls, the mice were fed a high-salt diet for an additional 4 weeks. Compared to Sham-mice, the expression levels of hypothalamic MR, serum glucocorticoid-induced kinase 1 (a marker of MR activity) and AT1R increased in PO-mice. Salt intake further increased the expression levels of these proteins only in PO-mice with the increases in sympathetic activity evaluated on the basis of the excretion of 24-h urinary norepinephrine excretion. Bilateral adrenalectomy or the intraperitoneal infusion of metyrapone, a corticosterone synthase inhibitor, attenuated salt-induced sympathoexcitation via inhibition of the hypothalamic MR and AT1R activity. These adrenalectomy-induced alterations disappeared after corticosterone replacement therapy. We also found decreased expression levels of 11β-hydroxysteroid dehydrogenase type 2, suggesting that corticosterone is apt to bind to MR. These results indicate that salt intake in PO-mice causes sympathoexcitation via, at least in part, corticosterone-induced MR and AT1R activation in the hypothalamus.

11β-hydroxysteroid dehydrogenases: intracellular gate-keepers of tissue glucocorticoid action

Glucocorticoid action on target tissues is determined by the density of "nuclear" receptors and intracellular metabolism by the two isozymes of 11β-hydroxysteroid dehydrogenase (11β-HSD) which catalyze interconversion of active cortisol and corticosterone with inert cortisone and 11-dehydrocorticosterone. 11β-HSD type 1, a predominant reductase in most intact cells, catalyzes the regeneration of active glucocorticoids, thus amplifying cellular action. 11β-HSD1 is widely expressed in liver, adipose tissue, muscle, pancreatic islets, adult brain, inflammatory cells, and gonads. 11β-HSD1 is selectively elevated in adipose tissue in obesity where it contributes to metabolic complications. Similarly, 11β-HSD1 is elevated in the ageing brain where it exacerbates glucocorticoid-associated cognitive decline. Deficiency or selective inhibition of 11β-HSD1 improves multiple metabolic syndrome parameters in rodent models and human clinical trials and similarly improves cognitive function with ageing. The efficacy of inhibitors in human therapy remains unclear. 11β-HSD2 is a high-affinity dehydrogenase that inactivates glucocorticoids. In the distal nephron, 11β-HSD2 ensures that only aldosterone is an agonist at mineralocorticoid receptors (MR). 11β-HSD2 inhibition or genetic deficiency causes apparent mineralocorticoid excess and hypertension due to inappropriate glucocorticoid activation of renal MR. The placenta and fetus also highly express 11β-HSD2 which, by inactivating glucocorticoids, prevents premature maturation of fetal tissues and consequent developmental "programming." The role of 11β-HSD2 as a marker of programming is being explored. The 11β-HSDs thus illuminate the emerging biology of intracrine control, afford important insights into human pathogenesis, and offer new tissue-restricted therapeutic avenues.

Role of brain corticosterone and aldosterone in central angiotensin II-induced hypertension

Circulating angiotensin II (Ang II) activates a central aldosterone-mineralocorticoid receptor neuromodulatory pathway, which mediates most of the Ang II-induced hypertension. This study examined whether specific central infusion of Ang II also activates this central aldosterone-mineralocorticoid receptor pathway. Intracerebroventricular infusion of Ang II at 1.0, 2.5, and 12.5 ng/min for 2 weeks caused dose-related increases in water intake, Ang II concentration in the cerebrospinal fluid, and blood pressure. Intracerebroventricular Ang II, at 2.5 and 12.5 ng/min, increased hypothalamic aldosterone and corticosterone, as well as plasma aldosterone and corticosterone without affecting plasma Ang II levels. Intracerebroventricular infusion of the aldosterone synthase inhibitor FAD286-but not the mineralocorticoid receptor blocker eplerenone-inhibited by ≈60% the Ang II-induced increase in hypothalamic aldosterone. Both blockers attenuated by ≈50% the increase in plasma aldosterone and corticosterone with only minimal effects on hypothalamic corticosterone. By telemetry, intracerebroventricular infusion of Ang II maximally increased blood pressure within the first day with no further increase over the next 2 weeks. Intracerebroventricular infusion of FAD286 or eplerenone did not affect the initial pressor responses but similarly prevented 60% to 70% of the chronic pressor responses to intracerebroventricular infusion of Ang II. These results indicate distinctly different patterns of blood pressure increase by circulating versus central Ang II and support the involvement of a brain aldosterone-mineralocorticoid receptor-activated neuromodulatory pathway in the chronic hypertension caused by both circulating and central Ang II.

Uninephrectomy reduces 11β-hydroxysteroid dehydrogenase type 1 and type 2 concomitantly with an increase in blood pressure in rats

Renal allograft donors are at risk of developing hypertension. Here, we hypothesized that this risk is at least in part explained by an enhanced intracellular availability of 11β-hydroxyglucocorticoids due to an increased 11β-hydroxysteroid dehydrogenase type 1 enzyme (11β-HSD1), an intracellular prereceptor activator of biologically inactive 11-ketocorticosteroids in the liver, and/or a diminished 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), an inactivator of 11β-hydroxyglucocorticoids in the kidney. To test this hypothesis, uninephrectomized (UNX) (n=9) and sham-operated (n=10) adult Sprague-Dawley rats were investigated. Mean arterial blood pressure and heart rate were measured continuously by telemetry for 6 days in week 5 after UNX. The mRNA of 11β-Hsd1 and 11β-Hsd2 in liver and kidney tissues were assessed by RT-PCR and the 11β-HSD activities were directly quantified in their corresponding tissues by determining the ratios of (tetrahydrocorticosterone+5α-tetrahydrocorticosterone)/tetrahydrodehydrocorticosterone ((THB+5α-THB)/THA) and of corticosterone/dehydrocorticosterone (B/A) by gas chromatography-mass spectrometry. The apparent total body activities of 11β-HSD1 and 11β-HSD2 were estimated using the urinary and plasma ratios of (THB+5α-THB)/THA and B/A. Mean arterial blood pressure was increased after UNX when compared with sham operation. Hepatic mRNA content of 11β-Hsd1 and hepatic, plasma, and urinary ratios of (THB+5α-THB)/THA were decreased after UNX, indicating diminished access of glucocorticoids to its receptors. In renal tissue, 11β-Hsd2 mRNA was reduced and B/A ratios measured in kidney, plasma, and urine were increased, indicating reduced 11β-HSD2 activity and enhanced access of glucocorticoids to mineralocorticoid receptors. Both 11β-HSD1 and 11β-HSD2 are downregulated after UNX in rats, a constellation considered to induce hypertension.

Central neuromodulatory pathways regulating sympathetic activity in hypertension

The classical neurotransmitters, glutamate and GABA, mediate fast (milliseconds) synaptic transmission and modulate its effectiveness through slow (seconds to minutes) signaling processes. Angiotensinergic pathways, from the lamina terminalis to the paraventricular nucleus (PVN)/supraoptic nucleus and rostral ventrolateral medulla (RVLM), are activated by stimuli such as circulating angiotensin type II (Ang II), cerebrospinal fluid (CSF) sodium ion concentration ([Na(+)]), and possibly plasma aldosterone, leading to sympathoexcitation, largely by decreasing GABA and increasing glutamate release. The aldosterone-endogenous ouabain (EO) pathway is a much slower neuromodulatory pathway. Aldosterone enhances EO release, and the latter increases chronic activity in angiotensinergic pathways by, e.g., increasing expression for Ang I receptor (AT(1)R) and NADPH oxidase subunits in the PVN. Blockade of this pathway does not affect the initial sympathoexcitatory and pressor responses but to a large extent, prevents chronic responses to CSF [Na(+)] or Ang II. Recruitment of these two neuromodulatory pathways allows the central nervous system (CNS) to shift gears to rapidly cause and sustain sympathetic hyperactivity in an efficient manner. Decreased GABA release, increased glutamate release, and enhanced AT(1)R activation in, e.g., the PVN and RVLM contribute to the elevated blood pressure in a number of hypertension models. In Dahl S rats and spontaneous hypertensive rats, high salt activates the CNS aldosterone-EO pathway, and the salt-induced hypertension can be prevented/reversed by specific CNS blockade of any of the steps in the cascade from aldosterone synthase to AT(1)R. Further studies are needed to advance our understanding of how and where in the brain these rapid, slow, and very slow CNS pathways are activated and interact in models of hypertension and other disease states associated with chronic sympathetic hyperactivity.

Central regulation of blood pressure by the mineralocorticoid receptor

Addition of mineralocorticoid receptor (MR) antagonists to standard therapy for heart failure, kidney disease, metabolic syndrome, and diabetes is increasing steadily in response to clinical trials demonstrating clear benefits. In addition to blocking deleterious activity of MR within the heart, vessels and kidneys, MR antagonists target MR in hemodynamic regulatory centers in the brain, thereby decreasing excessive sympathetic nervous system drive, vasopressin release, abnormal baroreceptor function, and circulating and tissue pro-inflammatory cytokines. However, brain MR are also involved with cognition, memory, affect and functions yet to be determined. Understanding specific central mechanisms involved in blood pressure regulation by MR is necessary for the development of agents to target downstream events specific to central hemodynamic regulation, not only to avoid the hypokalemia caused by inhibition of renal tubular MR, but also to avoid untoward long term effects of inhibiting brain MR that are not involved in blood pressure control.

NADPH oxidase-mediated Rac1 GTP activity is necessary for nongenomic actions of the mineralocorticoid receptor in the CA1 region of the rat hippocampus

Mineralocorticoid receptors (MRs) in the central nervous system play important roles in spatial memory, fear memory, salt sensitivity, and hypertension. Corticosterone binds to MRs to induce presynaptic vesicle release and postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor aggregation, which are necessary for induction of long-term potentiation under psychological stress. On the other hand, cognitive dysfunction is an important problem clinically in patients with hypertension, diabetes, and cerebral infarction, and all of these conditions are associated with an increase in reactive oxygen species (ROS) generation. Oxidative stress has been shown to modify the genomic actions of MRs in the peripheral organs; however, there have been no reports until now about the relation between the nongenomic actions of MRs and ROS in the central nervous system. In this study, we investigated the relationship between ROS and the nongenomic actions of MR. We examined the nongenomic actions of MR by measuring the slope of the field excitatory postsynaptic potentials and found that ROS induced an additive increase of these potentials, which was accompanied by Rac1 GTP activation and ERK1/2 phosphorylation. An NADPH oxidase inhibitor, apocynin, blocked the nongenomic actions of MRs. A Rac1 inhibitor, NSC23766, was also found to block synaptic enhancement and ERK1/2 phosphorylation induced by NADPH and corticosterone. We concluded that NADPH oxidase activity and Rac1 GTP activity are indispensable for the nongenomic actions of MRs and that Rac1 GTP activation induces ERK1/2 phosphorylation in the brain.

PVN adenovirus-siRNA injections silencing either NOX2 or NOX4 attenuate aldosterone/NaCl-induced hypertension in mice

Mineralocorticoid excess increases superoxide production by activating NADPH oxidase (NOX), and intracerebroventricular infusions of NADPH oxidase inhibitors attenuate aldosterone (Aldo)/salt-induced hypertension. It has been hypothesized that increased reactive oxygen species (ROS) in the brain may be a key mechanism in the development of hypertension. The present study investigated the brain regional specificity of NADPH oxidase and the role of NOX2 and NOX4 NADPH oxidase subunits in the hypothalamic paraventricular nucleus (PVN) in Aldo/salt-induced hypertension. PVN injections of adenoviral vectors expressing small interfering (si)RNA targeting NOX2 (AdsiRNA-NOX2) or NOX4 (AdsiRNA-NOX4) mRNAs were used to knock down NOX2 and NOX4 proteins. Three days later, delivery of Aldo (0.2 mg·kg(-1)·day(-1) sc) via osmotic pump commenced and 1% NaCl was provided in place of water. PVN injections of either AdsiRNA-NOX2 or AdsiRNA-NOX4 significantly attenuated the development of Aldo/NaCl-induced hypertension. In an additional study, Aldo/salt-induced hypertension was also significantly attenuated in NOX2 (genomic) knockout mice compared with wild-type controls. When animals from both functional studies underwent ganglionic blockade, there was a reduced fall in blood pressure in the NOX2 and NOX4 knockdown/knockout mice. Western blot analyses of the PVN of siRNA-NOX2- or siRNA-NOX4-injected mice confirmed a marked reduction in the expression of NOX2 or NOX4 protein. In cultured PVN neurons, silencing either NOX2 or NOX4 protein production by culturing PVN cells with siRNA-NOX2 or siRNA-NOX4 attenuated Aldo-induced ROS. These data indicate that both NOX2 and NOX4 in the PVN contribute to elevated sympathetic activity and the hypertensivogenic actions induced by mineralocorticoid excess.

Aldosterone-induced brain MAPK signaling and sympathetic excitation are angiotensin II type-1 receptor dependent

Angiotensin II (ANG II)-induced mitogen-activated protein kinase (MAPK) signaling upregulates angiotensin II type-1 receptors (AT(1)R) in hypothalamic paraventricular nucleus (PVN) and contributes to AT(1)R-mediated sympathetic excitation in heart failure. Aldosterone has similar effects to increase AT(1)R expression in the PVN and sympathetic drive. The present study was undertaken to determine whether aldosterone also activates the sympathetic nervous system via MAPK signaling and, if so, whether its effect is independent of ANG II and AT(1)R. In anesthetized rats, a 4-h intravenous infusion of aldosterone induced increases (P < 0.05) in phosphorylated (p-) p44/42 MAPK in PVN, PVN neuronal excitation, renal sympathetic nerve activity (RSNA), mean blood pressure (MBP), and heart rate (HR). Intracerebroventricular or bilateral PVN microinjection of the p44/42 MAPK inhibitor PD-98059 reduced the aldosterone-induced RSNA, HR, and MBP responses. Intracerebroventricular pretreatment (5 days earlier) with pooled small interfering RNAs targeting p44/42 MAPK reduced total and p-p44/42 MAPK, aldosterone-induced c-Fos expression in the PVN, and the aldosterone-induced increases in RSNA, HR, and MBP. Intracerebroventricular infusion of either the mineralocorticoid receptor antagonist RU-28318 or the AT(1)R antagonist losartan blocked aldosterone-induced phosphorylation of p44/42 MAPK and prevented the increases in RSNA, HR, and MBP. These data suggest that aldosterone-induced sympathetic excitation depends upon that AT(1)R-induced MAPK signaling in the brain. The short time course of this interaction suggests a nongenomic mechanism, perhaps via an aldosterone-induced transactivation of the AT(1)R as described in peripheral tissues.

The effect of a gap-junction blocker, carbenoxolone, on ischemic brain injury and cortical spreading depression

Cortical spreading depression (CSD) has been shown to cause secondary cell loss in experimental models of brain injury and in patients, and blocking of CSD is a potential neuroprotective strategy. Here we tested the hypothesis that gap junctions affect CSD under physiological conditions as well as infarct development in a rat two-vein occlusion model suited to study pathophysiology of the penumbra (n = 71). We applied the gap junction blocker carbenoxolone (CBX) or saline intra-ventricularly. Interestingly, CBX temporarily increased systemic blood pressure and cortical blood flow (41% and 53%, 15 min after 250 μg CBX). We induced CSD with cortical microinjection of potassium chloride (KCl), counted how many spontaneous CSDs after CSD induction were elicited and measured the propagation velocity. After 250 μg CBX administration, significant 37.5 ± 6.5 additional CSDs were seen. CSD velocity increased significantly after 50 μg and 250 μg CBX. Occlusion of two adjacent cortical veins using Rose Bengal dye and fiberoptic illumination followed by 250 μg CBX or saline showed a significant more than doubling of infarct volumes 7 days after CBX. The current experiments provide evidence that CBX can accelerate the initiation and propagation of CSD suggesting opening of gap junctions is not required for CSD propagation. Blocking gap junctions worsens outcome from focal cerebral ischemia. Hence, measures intended to improve spatial buffering via astroglial gap junctions could have therapeutic potential in disease processes involving CSD.

11β-hydroxysteroid dehydrogenases and the brain: from zero to hero, a decade of progress

Glucocorticoids have profound effects on brain development and adult CNS function. Excess or insufficient glucocorticoids cause myriad abnormalities from development to ageing. The actions of glucocorticoids within cells are determined not only by blood steroid levels and target cell receptor density, but also by intracellular metabolism by 11β-hydroxysteroid dehydrogenases (11β-HSD). 11β-HSD1 regenerates active glucocorticoids from their inactive 11-keto derivatives and is widely expressed throughout the adult CNS. Elevated hippocampal and neocortical 11β-HSD1 is observed with ageing and causes cognitive decline; its deficiency prevents the emergence of cognitive defects with age. Conversely, 11β-HSD2 is a dehydrogenase, inactivating glucocorticoids. The major central effects of 11β-HSD2 occur in development, as expression of 11β-HSD2 is high in fetal brain and placenta. Deficient feto-placental 11β-HSD2 results in a life-long phenotype of anxiety and cardiometabolic disorders, consistent with early life glucocorticoid programming.

EP₃ receptors mediate PGE₂-induced hypothalamic paraventricular nucleus excitation and sympathetic activation

Prostaglandin E(2) (PGE(2)), an important mediator of the inflammatory response, acts centrally to elicit sympathetic excitation. PGE(2) acts on at least four E-class prostanoid (EP) receptors known as EP(1), EP(2), EP(3), and EP(4). Since PGE(2) production within the brain is ubiquitous, the different functions of PGE(2) depend on the expression of these prostanoid receptors in specific brain areas. The type(s) and location(s) of the EP receptors that mediate sympathetic responses to central PGE(2) remain unknown. We examined this question using PGE(2), the relatively selective EP receptor agonists misoprostol and sulprostone, and the available selective antagonists for EP(1), EP(3), and EP(4). In urethane-anesthetized rats, intracerebroventricular (ICV) administration of PGE(2), sulprostone or misoprostol increased renal sympathetic nerve activity, blood pressure, and heart rate. These responses were significantly reduced by ICV pretreatment with the EP(3) receptor antagonist; the EP(1) and EP(4) receptor antagonists had little or no effect. ICV PGE(2) or misoprostol increased the discharge of neurons in the hypothalamic paraventricular nucleus (PVN). ICV misoprostol increased the c-Fos immunoreactivity of PVN neurons, an effect that was substantially reduced by the EP(3) receptor antagonist. Real-time PCR detected EP(3) receptor mRNA in PVN, and immunohistochemical studies revealed sparsely distributed EP(3) receptors localized in GABAergic terminals and on a few PVN neurons. Direct bilateral PVN microinjections of PGE(2) or sulprostone elicited sympathoexcitatory responses that were significantly reduced by the EP(3) receptor antagonist. These data suggest that EP(3) receptors mediate the central excitatory effects of PGE(2) on PVN neurons and sympathetic discharge.

Mechanisms mediating sodium-induced pressor responses in the PVN of Dahl rats

Intracerebroventricular infusion of Na(+)-rich artificial cerebrospinal fluid (aCSF) causes larger sympathetic and pressor responses in Dahl salt-sensitive (S) than -resistant (R) or Wistar rats. Enhanced activity of the aldosterone-"ouabain" pathway or decreased nitric oxide (NO) release may contribute to this enhanced responsiveness. Where in the brain these mechanisms interact is largely unknown. The present study evaluated whether Na(+) in the paraventricular nucleus (PVN) causes larger pressor responses in Dahl S (SS/Mcw) than R (Dahl SS.BN13) rats and whether mineralocorticoid receptors, benzamil-blockable Na(+) channels, "ouabain," angiotensin type 1 receptors, or NO mediates these enhanced responses. Na(+)-rich aCSF in the PVN caused 30-40% larger increases in blood pressure and heart rate in Dahl S than R or Wistar rats, whereas responses to ouabain, ANG II, or N(ω)-nitro-l-arginine methyl ester hydrochloride (l-NAME) in the PVN were the same. These responses to Na(+) were not affected by eplerenone, benzamil, or Fab fragments, whereas they were fully blocked by losartan, in Dahl S and R rats. l-NAME enhanced them more in Dahl R than S rats, thereby equalizing the responses in the two strains. Pressor responses to l-NAME in the PVN were attenuated by a high-salt diet in Dahl S, but not R, rats. The results indicate that acute and chronic increases in Na(+) concentration in the PVN inhibit NO release in the PVN of Dahl S, but not R, rats, thereby contributing to the enhanced pressor responses to Na(+) in Dahl S rats.

Display of Bombyx mori alcohol dehydrogenases on the Bacillus subtilis spore surface to enhance enzymatic activity under adverse conditions

Alcohol dehydrogenases (ADHs) are oxidoreductases catalyzing the reversible oxidation of alcohols to corresponding aldehydes or ketones accompanied by nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP) as coenzyme. ADHs attract major scientific and industrial interest for the evolutionary perspectives, afforded by their wide occurrence in nature, and for their use in industrial synthesis. However, the low activity of ADHs under extremes of pH and temperature often limits their application. To obtain ADH with high activity, in this study, we used Bombyx mori alcohol dehydrogenases (BmADH) as foreign gene and constructed a recombinant integrative plasmid pJS700-BmADH. This pJS700-BmADH was transformed into Bacillus subtilis by double cross-over and produced an amylase inactivated mutant. The fusion protein containing BmADH was expressed on the spore surface and recognized by BmADH-specific antibody. We also assayed the alcohol dehydrogenase activity of the fusion protein together with the native BmADH at different pH and temperature levels, which indicated the recombinant enzyme exhibits activity over wider ranges of temperature and pH than its native form, perhaps due to the resistance properties of B. subtilis spores against adverse conditions.

An ouabain-like factor is secreted from immortalized hypothalamic cells in an aldosterone-dependent manner

Ouabain-like factor (OLF) modulates blood pressure via sodium pump inhibition in the central nervous system and in the peripheral circulation. Ouabain-like factor (OLF) is thought to be produced in the adrenal gland and hypothalamus, and it may relate locally to the renin-angiotensin-aldosterone system. However, the evidence for the latter was obtained from in vivo experiments using animals. In the present study, we investigated ouabain production in the immortalized hypothalamic cell line N1. First, cell culture supernatant was collected from the immortalized hypothalamic cell line N1 at 0.5, 4, 8, and 24 h. A newly developed enzyme-linked immunosorbent assay (ELISA) that used anti-ouabain antibody showed that immunoreactivity in the supernatant was increased significantly at 24 vs. 0.5 h (0.01±0.004 vs. 0.16±0.033 pmol/mg protein, p<0.01). A combination of HPLC and ELISA was used to characterize N1 cell-derived OLI, showing that the highest peak of OLI had the same retention time as authentic ouabain. Thereafter, N1 cells were cultured with (1-10 μM) aldosterone, and supernatant was collected after 24 h of culture. In addition, N1 cells were cultured with 5 μM eplerenone, a mineralocorticoid receptor blocker, plus aldosterone. OLI was significantly increased in the supernatant of the cells cultured with 10 μM aldosterone (0.40±0.078 pmol/mg protein), and this increase was abolished by the addition of the aldosterone antagonist eplerenone (0.12±0.030 pmol/mg protein). These data suggest that the immortalized hypothalamic N1 cells secrete OLF and that aldosterone stimulates its secretion via mineralocorticoid receptors.

Functional variability in corticosteroid receptors is a major component of strain differences in fat deposition and metabolic consequences of enriched diets in rat

We aimed to distinguish mineralocorticoid (MR) from glucocorticoid receptor (GR) actions in the nutritional differences between the Fischer 344 (F344) and LOU/C (LOU) rat strains. The decrease of urinary Na+/K+ ratio induced via MR activation by aldosterone and decrease of circulating lymphocyte counts exerted via GR activation by dexamethasone revealed a higher efficiency of corticosteroid receptor in LOU than in F344 rats. Afterward, we submitted F344 and LOU male rats to adrenalectomy and to substitution treatments with agonists of MR or GR under 3 successive diets--standard, free choice between chow and pork lard, and an imposed high-fat/high-sugar diet--to explore the involvement of the interactions between activation of corticosteroid receptors and diet on food intake, body composition, and metabolic blood parameters in these rats. Lastly, we measured energy expenditure and substrate oxidization in various experimental conditions in LOU and F344 rats by indirect calorimetry. In LOU rats, we showed greater basal and MR-induced energy expenditure, diet-induced thermogenesis, and lipid oxidization. We showed that the F344 rat strain constitutes a relevant model of the unfavorable effects exerted by glucocorticoids via GR on food preference for high-calorie diets, abdominal fat deposition, diabetes, and other deleterious consequences of visceral obesity. Contrary to F344 rats, the LOU rats did not exhibit the expected visceral fat deposition linked to GR activation. This strain is therefore a relevant model of resistance to diet-induced obesity and to the deleterious effects exerted by glucocorticoids on metabolism.

Cloning, expression and characterization of alcohol dehydrogenases in the silkworm Bombyx mori

Alcohol dehydrogenases (ADH) are a class of enzymes that catalyze the reversible oxidation of alcohols to corresponding aldehydes or ketones, by using either nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP), as coenzymes. In this study, a short-chain ADH gene was identified in Bombyx mori by 5'-RACE PCR. This is the first time the coding region of BmADH has been cloned, expressed, purified and then characterized. The cDNA fragment encoding the BmADH protein was amplified from a pool of silkworm cDNAs by PCR, and then cloned into E. coli expression vector pET-30a(+). The recombinant His-tagged BmADH protein was expressed in E. coli BL21 (DE3), and then purified by metal chelating affinity chromatography. The soluble recombinant BmADH, produced at low-growth temperature, was instrumental in catalyzing the ethanol-dependent reduction of NAD(+), thereby indicating ethanol as one of the substrates of BmADH.

Hypothalamic oxytocin mediates adaptation mechanism against chronic stress in rats

Accumulation of continuous life stress (chronic stress) often causes gastric symptoms. Although central oxytocin has antistress effects, the role of central oxytocin in stress-induced gastric dysmotility remains unknown. Solid gastric emptying was measured in rats receiving acute restraint stress, 5 consecutive days of repeated restraint stress (chronic homotypic stress), and 7 consecutive days of varying types of stress (chronic heterotypic stress). Oxytocin and oxytocin receptor antagonist were administered intracerebroventricularly (icv). Expression of corticotropin-releasing factor (CRF) mRNA and oxytocin mRNA in the paraventricular nucleus (PVN) of the hypothalamus was evaluated by real-time RT-PCR. The changes of oxytocinergic neurons in the PVN were evaluated by immunohistochemistry. Acute stress delayed gastric emptying, and the delayed gastric emptying was completely restored after 5 consecutive days of chronic homotypic stress. In contrast, delayed gastric emptying persisted following chronic heterotypic stress. The restored gastric emptying following chronic homotypic stress was antagonized by icv injection of an oxytocin antagonist. Icv injection of oxytocin restored delayed gastric emptying induced by chronic heterotypic stress. CRF mRNA expression, which was significantly increased in response to acute stress and chronic heterotypic stress, returned to the basal levels following chronic homotypic stress. In contrast, oxytocin mRNA expression was significantly increased following chronic homotypic stress. The number of oxytocin-immunoreactive cells was increased following chronic homotypic stress at the magnocellular part of the PVN. Icv injection of oxytocin reduced CRF mRNA expression induced by acute stress and chronic heterotypic stress. It is suggested that the adaptation mechanism to chronic stress may involve the upregulation of oxytocin expression in the hypothalamus, which in turn attenuates CRF expression.

Central neuronal activation and pressor responses induced by circulating ANG II: role of the brain aldosterone-“ouabain” pathway

An increase in plasma ANG II causes neuronal activation in hypothalamic nuclei and a slow pressor response, presumably by increasing sympathetic drive. We evaluated whether the activation of a neuromodulatory pathway, involving aldosterone and “ouabain,” is involved in these responses. In Wistar rats, the subcutaneous infusion of ANG II at 150 and 500 ng·kg−1·min−1 gradually increased blood pressure up to 60 mmHg at the highest dose. ANG II at 500 ng·kg−1·min−1 increased plasma ANG II by 4-fold, plasma aldosterone by 25-fold, and hypothalamic aldosterone by 3-fold. The intracerebroventricular infusion of an aldosterone synthase (AS) inhibitor prevented the ANG II-induced increase in hypothalamic aldosterone without affecting the increase in plasma aldosterone. Neuronal activity, as assessed by Fra-like immunoreactivity, increased transiently in the subfornical organ (SFO) but progressively in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). The central infusion of the AS inhibitor or a mineralocorticoid receptor blocker markedly attenuated the ANG II-induced neuronal activation in the PVN but not in the SON. Pressor responses to ANG II at 150 ng·kg−1·min−1 were abolished by an intracerebroventricular infusion of the AS inhibitor. Pressor responses to ANG II at 500 ng·kg−1·min−1 were attenuated by the central infusion of the AS inhibitor or the mineralocorticoid receptor blocker by 70–80% and by Digibind (to bind “ouabain”) by 50%. These results suggest a novel central nervous system mechanism for the ANG II-induced slow pressor response, i.e., circulating ANG II activates the SFO, leading to the direct activation of the PVN and SON, and, in addition, via aldosterone-dependent amplifying mechanisms, causes sustained activation of the PVN and thereby hypertension.

Brain renin–angiotensin–aldosterone system and ventricular remodeling after myocardial infarct: a reviewThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

After a myocardial infarct (MI), a variety of mechanisms contribute to progressive cardiac remodeling and dysfunction. Progressive activation of central sympathoexcitatory pathways appears to depend on a neuromodulatory pathway, involving local production of aldosterone and release of endogenous ouabain-like compounds (‘ouabain’) possibly from magnocellular neurons in the supraoptic and paraventricular nuclei. ‘Ouabain’ may lower the membrane potential of neurons and thereby enhance activity of angiotensinergic pathways. These central pathways appear to coordinate progressive activation of several peripheral mechanisms such as sympathetic tone and circulating and cardiac renin–angiotensin–aldosterone system (RAAS). Central blockade of aldosterone production, mineralocorticoid receptors, ‘ouabain’ activity, or AT1 receptors similarly prevents activation of these peripheral mechanisms. Cardiac remodeling after MI involves progressive left ventricular dilation, fibrosis, and decrease in contractile performance. Central blockade of this neuromodulatory pathway causes a marked attenuation of the remodeling and dysfunction, presumably by inhibiting increases in (cardiac) sympathetic activity and RAAS. At the cellular level, these systems may contribute to the cardiac remodeling by activating proinflammatory cytokines and cardiac myocyte apoptosis. New therapeutic approaches, specifically preventing activation of this brain neuromodulatory pathway, may lead to more optimal and specific approaches to the prevention of heart failure after MI.

Systemically administered tempol reduces neuronal activity in paraventricular nucleus of hypothalamus and rostral ventrolateral medulla in rats

OBJECTIVE

Systemic administration of the superoxide scavenger tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) reduces blood pressure (BP), heart rate (HR) and sympathetic nerve activity in normotensive and hypertensive animals. The global nature of the depressor response to tempol suggests an inhibitory influence on cardiovascular presympathetic regions of the brain. This study examined several possible mechanisms for such an effect.

METHODS AND RESULTS

In urethane anesthetized rats, as expected, intravenous tempol (120 microg mol/kg) reduced mean arterial pressure, HR and renal sympathetic nerve activity (RSNA). Concomitant central neuronal recordings revealed reduced spontaneous discharge (spikes/s) of neurons in the paraventricular nucleus of hypothalamus (from 2.9 +/- 0.4 to 0.8+/- 0.2) and the rostral ventrolateral medulla (RVLM; from 9.8 +/- 0.5 to 7.2 +/-0.4), two cardiovascular and autonomic regions of the brain. Baroreceptor-denervated rats had exaggerated sympathetic and cardiovascular responses. Pretreatment with the hydroxyl radical scavenger dimethyl sulfoxide (intravenous) attenuated the tempol-induced decreases in BP, HR and RSNA, but the nitric oxide synthesis inhibitor NG-nitro-L-arginine methyl ester (intravenous or intracerebroventricular) had no effect.

CONCLUSION

These findings suggest that systemically administered tempol acts upon neurons in paraventricular nucleus and RVLM to reduce BP, HR and RSNA, perhaps by reducing the influence of reactive oxygen species in those regions. The arterial baroreflex modulates the depressor responses to tempol. These central mechanisms must be considered in interpreting data from studies using systemically administered tempol to assess the role of reactive oxygen species in cardiovascular regulation.

Role of central nervous system aldosterone synthase and mineralocorticoid receptors in salt-induced hypertension in Dahl salt-sensitive rats

In Dahl salt-sensitive (S) rats, high salt intake increases cerebrospinal fluid (CSF) Na+ concentration ([Na+]) and blood pressure (BP). Intracerebroventricular (ICV) infusion of a mineralocorticoid receptor (MR) blocker prevents the hypertension. To assess the role of aldosterone locally produced in the brain, we evaluated the effects of chronic central blockade with the aldosterone synthase inhibitor FAD286 and the MR blocker spironolactone on changes in aldosterone and corticosterone content in the hypothalamus and the increase in CSF [Na+] and hypertension induced by high salt intake in Dahl S rats. After 4 wk of high salt intake, plasma aldosterone and corticosterone were not changed, but hypothalamic aldosterone increased by ∼35% and corticosterone tended to increase in Dahl S rats, whereas both steroids decreased by ∼65% in Dahl salt-resistant rats. In Dahl S rats fed the high-salt diet, ICV infusion of FAD286 or spironolactone did not affect the increase in CSF [Na+]. ICV infusion of FAD286 prevented the increase in hypothalamic aldosterone and 30 mmHg of the 50-mmHg BP increase induced by high salt intake. ICV infusion of spironolactone fully prevented the salt-induced hypertension. These results suggest that, in Dahl S rats, high salt intake increases aldosterone synthesis in the hypothalamus and aldosterone acts as the main MR agonist activating central pathways contributing to salt-induced hypertension.

Development of chemosensitivity in neurons from the nucleus tractus solitarii (NTS) of neonatal rats

We studied the development of chemosensitivity during the neonatal period in rat nucleus tractus solitarii (NTS) neurons. We determined the percentage of neurons activated by hypercapnia (15% CO(2)) and assessed the magnitude of the response by calculating the chemosensitivity index (CI). There were no differences in the percentage of neurons that were inhibited (9%) or activated (44.8%) by hypercapnia or in the magnitude of the activated response (CI 164+/-4.9%) in NTS neurons from neonatal rats of all ages. To assess the degree of intrinsic chemosensitivity in these neurons we used chemical synaptic block medium and the gap junction blocker carbenoxolone. Chemical synaptic block medium slightly decreased basal firing rate but did not affect the percentage of NTS neurons that responded to hypercapnia at any neonatal age. However, in neonates aged Collapse

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MESH Headings

• Age Factors
• Analysis of Variance
• Animals
• Animals, Newborn
• Carbenoxolone/pharmacology
• Carbon Dioxide/pharmacology
• Chemoreceptor Cells/physiology
• Drug Interactions
• Electric Stimulation
• Hypercapnia/physiopathology
• In Vitro Techniques
• Membrane Potentials/drug effects
• Membrane Potentials/physiology
• Patch-Clamp Techniques/methods
• Rats
• Rats, Sprague-Dawley
• Solitary Nucleus/cytology
• Solitary Nucleus/growth & development

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Grants

• R01 HL056683-08 NHLBI NIH HHS
• HL-56683 NHLBI NIH HHS
• R01 HL056683-10 NHLBI NIH HHS
• R01 HL056683-09A1 NHLBI NIH HHS
• R01 HL056683-11 NHLBI NIH HHS
• R01 HL056683 NHLBI NIH HHS

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Affiliation(s)

Susan C. Conrad Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435
Nicole L. Nichols Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435
Nick A. Ritucci Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435
Jay B. Dean Department of Molecular Pharmacology and Physiology, University of South Florida College of Medicine, 12901 Bruce B. Downs Boulevard, Tampa, FL 33612
Robert W. Putnam Department of Neuroscience, Cell Biology and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435

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Properties of gap junction blockers and their behavioural, cognitive and electrophysiological effects: animal and human studies

Gap junctions play an important role in brain physiology. They synchronize neuronal activity and connect glial cells participating in the regulation of brain metabolism and homeostasis. Gap junction blockers (GJBs) include various chemicals that impair gap junction communication, disrupt oscillatory neuronal activity over a wide range of frequencies, and decrease epileptic discharges. The behavioural and clinical effects of GJBs suggest that gap junctions can be involved in the regulation of locomotor activity, arousal, memory, and breathing. Severe neuropsychiatric side effects suggest the involvement of gap junctions in mechanisms of consciousness. Unfortunately, the available GJBs are not selective and can bind to targets other than gap junctions. Other problems in behavioural studies include the possible adverse effects of GJBs, for example, retinal toxicity and hearing disturbances, changes in blood-brain transport, and the metabolism of other drugs. Therefore, it is necessary to design experiments properly to avoid false, misleading or uninterpretable results. We review the pharmacological properties and electrophysiological, behavioural and cognitive effects of the available gap junction blockers, such as carbenoxolone, glycyrrhetinic acid, quinine, quinidine, mefloquine, heptanol, octanol, anandamide, fenamates, 2-APB, several anaesthetics, retinoic acid, oleamide, spermine, aminosulfonates, and sodium propionate. It is concluded that despite a number of different problems, the currently used gap junction blockers could be useful tools in pharmacology and neuroscience.

Sex differences and central protective effect of 17beta-estradiol in the development of aldosterone/NaCl-induced hypertension

The present study tested the hypotheses that male and female rats respond differently to subcutaneous infusions of aldosterone (Aldo; 1.8 microg.kg(-1).h(-1), 1% NaCl to drink; 28 days) and that central estrogen plays a protective role against the development of hypertension. In rats with blood pressure (BP) and heart rate (HR) measured by Data Sciences International telemetry, chronic Aldo/NaCl treatment induced a greater increase in BP in males (Delta25.4 +/- 2.4 mmHg) than in females (Delta7.1 +/- 2.2 mmHg). Gonadectomy augmented Aldo/NaCl-induced hypertension in females (Delta18.2 +/- 2.0 mmHg) but had no effect in males (Delta23.1 +/- 2.9 mmHg). Immunohistochemistry for Fra-like activity was higher in the paraventricular nucleus of intact males, castrated males, and ovariectomized (OVX) females compared with intact females after 28 days of Aldo/NaCl treatment. In intact males, central 17beta-estradiol (E(2)) inhibited the Aldo/NaCl increase in BP (Delta10.5 +/- 0.8) compared with that in central vehicle plus systemic Aldo/NaCl (Delta26.1 +/- 2.5 mmHg) rats. Combined administration of E(2) and estrogen receptor antagonist ICI182780 (ICI) blocked the protective effect of E(2) (Delta23.2 +/- 2.4 mmHg). In intact females central, but not peripheral, infusions of ICI augmented the Aldo/NaCl (Delta20.4 +/- 1.8 mmHg) BP increase. Finally, ganglionic blockade after Aldo infusions resulted in a smaller reduction in BP in intact females (-23.9 +/- 2.5 mmHg) and in central estrogen-treated males (-30.2 +/- 1.0 mmHg) compared with other groups (intact males, -39.3 +/- 3.4; castrated males, -41.8 +/- 1.9; intact males with central E(2) + ICI, -42.3 +/- 2.1; OVX females, -40.3 +/- 3.3; and intact females with central ICI, -39.1 +/- 1.3 mmHg). Chronic Aldo infusion produced increases in NaCl intake and decreases in HR that were both similar in all groups. Taken together, the results indicate that central estrogen plays a protective role in the development of Aldo/NaCl-induced hypertension and that this may result from reduced sympathetic outflow.

Aldosterone in the brain

Pharmacological and physiological phenomena suggest that cells somewhere inside the central nervous system are responsive to aldosterone. Here, we present the fundamental physiological limitations for aldosterone action in the brain, including its limited blood-brain barrier penetration and its substantial competition from glucocorticoids. Recently, a small group of neurons with unusual sensitivity to circulating aldosterone were identified in the nucleus of the solitary tract. We review the discovery and characterization of these neurons, which express the enzyme 11beta-hydroxysteroid dehydrogenase type 2, and consider alternative proposals regarding sites and mechanisms for mineralocorticoid action within the brain.

Mechanisms in the PVN mediating local and central sodium-induced hypertension in Wistar rats

Sympathoexcitatory and hypertensive responses to central infusion of Na(+)-rich artificial cerebrospinal fluid (aCSF) are enhanced by aldosterone and mediated by mineralocorticoid receptors (MRs) and benzamil-blockable Na(+) influx, leading to "ouabain" release and ANG II type 1 (AT(1)) receptor stimulation. The present study evaluated the functional role of these mechanisms in the paraventricular nucleus (PVN). In conscious Wistar rats, Na(+)-rich aCSF was infused either directly into the PVN or intracerebroventricularly preceded by aldosterone and blockers. Infusion of Na(+)-rich aCSF in the PVN caused gradual increases in blood pressure (BP) and heart rate (HR). Aldosterone and a subpressor dose of ouabain in the PVN alone did not affect BP and HR but enhanced responses to Na(+). Eplerenone, benzamil, and "ouabain"-binding Fab fragments only blocked the enhancement by aldosterone, whereas losartan blocked all responses to Na(+)-rich aCSF in the PVN. Increases in BP and HR by intracerebroventricular infusion of Na(+)-rich aCSF were enhanced by aldosterone infused intracerebroventricularly, but not in the PVN. Telmisartan in the PVN again blocked all responses. In contrast, both eplerenone and benzamil in the PVN did not change the pressor responses to intracerebroventricular infusion of aldosterone and Na(+)-rich aCSF. These findings indicate that AT(1) receptors in the PVN mediate the responses to Na(+)-rich aCSF and their enhancement by aldosterone, both locally in the PVN or in the general CSF. MRs, benzamil-blockable Na(+) channels or transporters, and "ouabain" can be functionally active in the PVN, but in Wistar rats appear not to contribute to the pressor responses to short-term increases in CSF [Na(+)].