SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Aldosterone

171

Besides the kidneys, the gastrointestinal tract is the principal organ responsible for sodium homeostasis. For sodium transport across the cell membranes the epithelial sodium channel (ENaC) is of pivotal relevance. The ENaC is mainly regulated by mineralocorticoid receptor mediated actions. The MR activation by endogenous 11β-hydroxy-glucocorticoids is modulated by the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). Here we present evidence for intestinal segment specific 11β-HSD2 expression and hypothesize that a high salt intake and/or uninephrectomy (UNX) affects colonic 11β-HSD2, MR and ENaC expression. The 11β-HSD2 activity was measured by means of 3H-corticosterone conversion into 3H-11-dehydrocorticosterone in Sprague Dawley rats on a normal and high salt diet. The activity increased steadily from the ileum to the distal colon by a factor of about 3, an observation in line with the relevance of the distal colon for sodium handling. High salt intake diminished mRNA and protein of 11β-HSD2 by about 50% (p<0.001) and reduced the expression of the MR (p<0.01). The functionally relevant ENaC-β and ENaC-γ expression, a measure of mineralocorticoid action, diminished by more than 50% by high salt intake (p<0.001). The observed changes were present in rats with and without UNX. Thus, colonic epithelial cells appear to contribute to the protective armamentarium of the mammalian body against salt overload, a mechanism not modulated by UNX.

Concepts: Epithelial sodium channel, Epithelium, Stomach, Digestive system, Sodium, Laboratory rat, Aldosterone, Protein

168

Aldosterone synthase (CYP11B2) is a promising therapeutic target for the treatment of cardiovascular diseases related to abnormally high aldosterone levels. On the basis of our previously identified lead compounds I-III, a series of 3-pyridinyl substituted aliphatic cycles were designed, synthesized and tested as CYP11B2 inhibitors. Aromaticity abolishment of the core was successfully applied to overcome the undesired CYP1A2 inhibition. This study resulted in a series of potent and selective CYP11B2 inhibitors, with compound 12 (IC(50) = 21 nM, SF = 50) as the most promising one, which shows no inhibition toward CYP1A2 at 2 µM. The design conception demonstrated in this study can be helpful in the optimization of CYP inhibitor drugs regarding CYP1A2 selectivity.

Concepts: Zona glomerulosa, Corticosterone, Xanthine oxidase inhibitor, Aldosterone, Aldosterone synthase, Inhibitor, Cytochrome P450, Enzyme inhibitor

155

Primary aldosteronism (PA) secondary to excessive and/or autonomous aldosterone secretion from the renin angiotensin system (RAS) accounts for approximately 10% of cases of hypertension and is primarily caused by bilateral adrenal hyperplasia (BAH) or aldosterone-producing adenomas (APAs). Although the diagnosis has traditionally been supported by low serum potassium levels, normokalemic and even normotensive forms of PA have been identified expanding further the clinical phenotype. Morever, recent evidence has shown that serum aldosterone correlates with increased blood pressure in the general population and even moderately raised aldosterone levels are linked to increased cardiovascular morbidity and mortality. In addition, aldosterone antagonists are effective in blood pressure control even in patients without evidence of dysregulated aldosterone secretion. These findings indicate a higher prevalence of aldosterone excess among hypertensive patients than previously considered that could be attributed to disease heterogeneity, aldosterone level fluctuations related to an adrenocorticotropin (ACTH) effect, or inadequate sensitivity of current diagnostic means to identify apparent aldosterone excess. In addition, functioning aberrant receptors expressed in the adrenal tissue have been found in a subset of PA cases that could also be related to its pathogenesis. Recently a number of specific genetic alterations, mainly involving ion homeostasis across the membrane of zona glomerulosa, have been detected in approximately 50% of patients with APAs. Although specific genotype/phenotype correlations have not been clearly identified, differential expression of these genetic alterations could also account for the wide clinical phenotype, variations in disease prevalence and performance of diagnostic tests. In the present review, we critically analyze current means used to diagnose PA along with the role that ACTH, aberrant receptor expression and genetic alterations may exert, and provide evidence for an increased prevalence of aldosterone dysregulation in patients with essential hypertension and pre-hypertension.

Concepts: Hyperaldosteronism, Kidney, Cortisol, Renin, Aldosterone, Blood pressure, Hypertension, Renin-angiotensin system

44

Virgin coconut oil (VCO) has been consumed worldwide for various health-related reasons and some of its benefits have been scientifically evaluated. Medium-chain fatty acids were found to be a potential antidepressant functional food; however, this effect had not been evaluated in VCO, which is rich in polyphenols and medium-chain fatty acids. The aim of this study was to evaluate the antistress and antioxidant effects of VCO in vivo, using mice with stress-induced injury. The antistress effect of VCO (administered per os, at a dose of 10 ml/kg body weight) was evaluated using the forced swim test and chronic cold restraint stress models. VCO was able to reduce immobility time and restore oxidative stress in mice post-swim test. Furthermore, mice treated with VCO were found to exhibit higher levels of brain antioxidants, lower levels of brain 5-hydroxytryptamine and reduced weight of the adrenal glands. Consequently, the serum cholesterol, triglyceride, glucose and corticosterone levels were also lower in VCO-treated mice. These results suggest the potential value of VCO as an antistress functional oil.

Concepts: Aldosterone, Triglyceride, Saturated fat, Vitamin C, Fatty acid, Antioxidant, Cholesterol, Nutrition

29

Successful treatment of hypertension is difficult despite the availability of several classes of antihypertensive drug, and the value of strategies to combat the effect of adverse lifestyle behaviours on blood pressure. In this paper, we discuss two promising therapeutic alternatives for patients with resistant hypertension: novel drugs, including new pharmacological classes (such as vasopeptidase inhibitors and aldosterone synthase inhibitors) and new molecules from present pharmacological classes with additional properties in blood-pressure or metabolism pathways; and new procedures and devices, including stimulation of arterial baroreceptors and catheter-based renal denervation. Although several pharmacological targets have been discovered with promising preclinical results, the clinical development of novel antihypertensive drugs has been more difficult and less productive than expected. The effectiveness and safety of new devices and procedures should be carefully assessed in patients with resistant hypertension, thus leading to a new era of outcome trials and evidence-based guidelines.

Concepts: Clinical trial, Myocardial infarction, Aldosterone, Thiazide, Pharmacology, Antihypertensive agents, Antihypertensive drug, Blood pressure

28

Aldosterone (Aldo) is involved in arterial stiffness and heart failure, but the mechanisms have remained unclear. Galectin-3 (Gal-3), a β-galactoside-binding lectin, plays an important role in inflammation, fibrosis, and heart failure. We investigated here whether Gal-3 is involved in Aldo-induced vascular fibrosis.

Concepts: Cholesterol, Heart, Aldosterone, Blood pressure, Blood vessel

28

Vasopressin modulates sodium reabsorption in the collecting duct through adenylyl cyclase-stimulated cyclic AMP, which exists as multiple isoforms; the specific isoform involved in vasopressin-stimulated sodium transport is unknown. To assess this, we studied mice deficient in adenylyl cyclase type VI specifically in the principal cells of the collecting duct. Knockout mice had increased urine volume and reduced urine sodium concentration, but regardless of the level of sodium intake, they did not exhibit significant alterations in urinary sodium excretion, arterial pressure, or pulse rate. Plasma renin concentration was elevated in knockout mice, however, suggesting a compensatory response. Valsartan significantly reduced arterial pressure in knockout mice but not in controls. Knockout mice had decreased renal cortical mRNA content of all three epithelial sodium channel (ENaC) isoforms, and total cell sodium channel isoforms α and γ were reduced in these animals. Patch-clamp analysis of split-open cortical collecting ducts revealed no difference in baseline activity of sodium channels, but knockout mice had abolished vasopressin-stimulated ENaC open probability and apical membrane channel number. In summary, these data suggest that adenylyl cyclase VI mediates vasopressin-stimulated ENaC activity in the kidney.

Concepts: Renin, Collecting duct system, Renal physiology, Nephron, Aldosterone, Blood pressure, Sodium, Kidney

28

AIMS: In diseases with proteinuria, e.g. nephrotic syndrome and preeclampsia, there often is suppression of plasma renin-angiotensin-aldosterone system components, expansion of extracellular volume and avid renal sodium retention. Mechanisms of sodium retention in proteinuria are reviewed. METHODS AND RESULTS: In animal models of nephrotic syndrome, the amiloride-sensitive epithelial sodium channel ENaC is activated while more proximal renal Na(+) transporters are down-regulated. With suppressed plasma aldosterone concentration and little change in ENaC abundance in nephrotic syndrome, the alternative modality of proteolytic activation of ENaC has been explored. Proteolysis leads to putative release of an inhibitory peptide from the extracellular domain of the gamma ENaC subunit. This leads to full activation of the channel. Plasminogen has been demonstrated in urine from patients with nephrotic syndrome and preeclampsia. Urine plasminogen correlates with urine albumin and is activated to plasmin within the urinary space by uPA. This agrees with aberrant filtration across an injured glomerular barrier independent of the primary disease. Pure plasmin and urine samples containing plasmin activate inward current in single murine collecting duct cells. In the present paper, it is shown that human lymphocytes may be used to uncover the effect of urine-plasmin on amiloride- and aprotinin-sensititve inward currents. Data from hypertensive rat models show that protease inhibitors may attenuate blood pressure. CONCLUSION: Aberrant filtration of plasminogen and conversion within the urinary space to plasmin may activate gamma ENaC proteolytically and contribute to inappropriate NaCl retention and edema in acute proteinuric conditions and to hypertension in diseases with chronic microalbuminuria/proteinuria. © 2012 The Authors Acta Physiologica © 2012 Scandinavian Physiological Society.

Concepts: Potassium, Blood pressure, Sodium, Epithelial sodium channel, Hypertension, Aldosterone, Nephrotic syndrome, Kidney

28

Aldosterone modulates the activity of the epithelial sodium channel (ENaC) through changes in its trafficking, membrane expression and open probability. Plasma levels of aldosterone are decreased in preeclampsia. Herein we postulated that if aldosterone regulates ENaC expression then its expression should be decreased in preeclampsia. We found a diminished expression of the three subunits of the ENaC in the membranes of preeclamptic placentas in comparison with the normal ones. Although the role of ENaC in placental tissues is poorly understood, these differences may have consequences for the ion transport involved in the pathophysiology of preeclampsia.

Concepts: Triamterene, Cell membrane, Atrial natriuretic peptide, Amiloride, Placenta, Sodium, Aldosterone, Epithelial sodium channel

28

Inhaled corticosteroids (ICS) are drugs of choice for persistent asthma. Less than 500 µg/d of fluticasone are believed to be safe. We found 92 cases of adrenal suppression in PubMed; among these cases there were 13 children who took 500 µg/d or less of fluticasone. Adrenal insufficiency was diagnosed in a 7-year-old boy on 460 µg ICS for 16 months, with a diagnosis of chronic persistent asthma. A random cortisol was nondetectable as was an early morning cortisol. ICS have greatly improved the day-to-day lives of children with chronic persistent asthma. Parents of children younger than 12 years, who use at least 400 µg of inhaled fluticasone (or bioequivalent), must be given oral and written instructions about warning symptoms of hypocortisolism. Major stress such as surgery, gastrointestinal, bronchopulmonary, or other systemic infections, and heat stress may mandate a written plan of action for use by hospital physicians.

Concepts: Epinephrine, Adrenal cortex, Aldosterone, Glucocorticoid, Cortisol, Asthma, Corticosteroid, Adrenal insufficiency