High salt intake down-regulates colonic mineralocorticoid receptors, epithelial sodium channels and 11β-hydroxysteroid dehydrogenase type 2

Lactobacillus rhamnosus Encapsulated in Alginate/Chitosan Microgels Manipulates the Gut Microbiome to Ameliorate Salt-Induced Hepatorenal Injury

As the essential regulator of intestinal bacterial diversity, probiotics are a potential treatment for chronic high-salt diet (HSD)–induced metabolic dysfunction. Probiotic cells entrapped in microgels have been confirmed as being more effective than free cells in protecting bacteria against unfavorable conditions, that is, enhancing their stress resistance. This study explored the physiological mechanism by which probiotic microgels relieve HSD–induced hepatorenal injury. Herein, Lactobacillus rhamnosus was encapsulated in alginate-chitosan microgels which the percentage of alginate/chitosan was applied 1.5:0.5 (w/w) in this system, and the encapsulation significantly improved the probiotic viability in simulated gastrointestinal conditions. Mice were fed an HSD with L. rhamnosus (SDL) or L. rhamnosus microgels (SDEL). After 8 weeks of administration, dietary sodium was confirmed as inducing the hepatic and renal damages in mice, based on indicators, including serum biomarker levels, histopathological features of tissues, and pro-inflammatory cytokine contents in blood levels. However, the serum levels of urea nitrogen, creatinine, uric acid, glutamic-pyruvic transaminase, glutamic-oxalacetic transaminase, and alkaline phosphatase in the SDL and SDEL-fed mice were significantly lowered compared to the HSD-fed mice, especially in the SDEL group. HSD increased the abundances of Anaeroplasma, Enterorhabdus, Parvibacter, and Bacteroides, while the microgels increased the abundances of Lactobacillus, Bifidobacterium, Mucispirillum, and Faecalibaculum. Significant variations of fecal metabolome were validated for SDEL-treated mice, containing those linked to entero-hepatic circulation (e.g., cholic acid), carbohydrate metabolism (i.e., _L-lactic acid), and increased antioxidants including citric acid. Furthermore, the probiotic microgels ameliorated intestinal damage by improving barrier and absorption functions. These results augmented existing knowledge on probiotic application for salt toxicity.

Bile acids and salt-sensitive hypertension: a role of the gut-liver axis

Salt-sensitivity of blood pressure (SSBP) affects 50% of the hypertensive and 25% of the normotensive populations. Importantly, SSBP is associated with increased risk for mortality in both populations independent of blood pressure. Despite its deleterious effects, the pathogenesis of SSBP is not fully understood. Emerging evidence suggests a novel role of bile acids in salt-sensitive hypertension and that they may play a crucial role in regulating inflammation and fluid volume homeostasis. Mechanistic evidence implicates alterations in the gut microbiome, the epithelial sodium channel (ENaC), the farnesoid X receptor, and the G protein-coupled bile acid receptor TGR5 in bile acid-mediated effects on cardiovascular function. The mechanistic interplay between excess dietary sodium-induced alterations in the gut microbiome and immune cell activation, bile acid signaling, and whether such interplay may contribute to the etiology of SSBP is still yet to be defined. The main goal of this review is to discuss the potential role of bile acids in the pathogenesis of cardiovascular disease with a focus on salt-sensitive hypertension.

Antibiotic Disruption of the Gut Microbiota Enhances the Murine Hepatic Dysfunction Associated With a High-Salt Diet

Epidemiological and experimental evidence indicates that antibiotic exposure is related to metabolic malfunctions, such as obesity and non-alcoholic fatty liver disease (NAFLD). Liver impairment and hypertrophy of adipose cells are related to high salt consumption. This research aims to investigated the physiological mechanism of a high salt diet (HSD) enhanced antibiotic-induced hepatic injury and mitochondrial abnormalities in mice. The mice were fed a HSD with or without penicillin G (PEN) for 8 weeks and the gut metabolome, untargeted faecal metabolomics, and intestinal function were evaluated. The results revealed that HSD, PEN and their combination (HSPEN) significantly changed the gut microbial community. HSPEN mice exhibited more opportunistic pathogens (such as Klebsiella and Morganella) and reduced probiotic species (including Bifidobacterium and Lactobacillus). The main variations in the faecal metabolites of the HSPEN group were identified, including those connected with entero-hepatic circulation (including bile acids), tryptophan metabolism (i.e., indole derivatives) and lipid metabolism (e.g., erucic acid). Furthermore, increased intestinal permeability and immunologic response caused greater hepatic damage in the HSPEN group compared to the other groups. These findings may have important implications for public health.

Intake of processed meat, but not sodium, is associated with risk of colorectal cancer: Evidence from a large prospective cohort and two-sample Mendelian randomization

BACKGROUND & AIMS

Processed meat and high sodium intake are common in Western diet. The objective was to examine their independent effects on the risk of colorectal cancer (CRC).

METHODS

We performed both observational analysis with UK Biobank and genetic analysis with Mendelian randomization (MR). The 24-h urinary sodium (UNa) and reported intake of processed meat were fitted on incident CRC by multivariable Cox proportional hazard model, adjusted for covariates, such as age, gender, family history, etc. Different sodium measures were used for sensitivity analyses. Two-sample MR analyses were performed using summary data from genome-wide association studies of UNa and CRC. Multivariable MR was adjusted for body mass index.

RESULTS

We included 415 524 eligible participants from UK Biobank. During a median follow-up of 11.1 years, 2663 participants were diagnosed with CRC. High intake of processed meat independently increased risk of CRC by 23% (HR 1.23; 95% CI: 1.03 to 1.46), but 24-h UNa was not significantly associated with CRC (HR 0.96; 95% CI: 0.87 to 1.06). Furthermore, MR also showed little evidence for the effect of UNa on CRC (OR 1.02; 95% CI: 0.11 to 9.42). Sensitivity analyses showed consistent results across different measurements of sodium intake.

CONCLUSIONS

Intake of processed meat had an independent effect on the risk of CRC, but the risk was not associated with sodium level. Reduction of processed meat intake may be an effective strategy for CRC prevention, while sodium reduction should still be recommended to achieve other health benefits.

Function and Regulation of the Epithelial Na+ Channel ENaC

The Epithelial Na⁺ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na⁺ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.

Classic and Nonclassic Apparent Mineralocorticoid Excess Syndrome

CONTEXT

Arterial hypertension (AHT) is one of the most frequent pathologies in the general population. Subtypes of essential hypertension characterized by low renin levels allowed the identification of 2 different clinical entities: aldosterone-mediated mineralocorticoid receptor (MR) activation and cortisol-mediated MR activation.

EVIDENCE ACQUISITION

This review is based upon a search of Pubmed and Google Scholar databases, up to August 2019, for all publications relating to endocrine hypertension, apparent mineralocorticoid excess (AME) and cortisol (F) to cortisone (E) metabolism.

EVIDENCE SYNTHESIS

The spectrum of cortisol-mediated MR activation includes the classic AME syndrome to milder (nonclassic) forms of AME, the latter with a much higher prevalence (7.1%) than classic AME but different phenotype and genotype. Nonclassic AME (NC-AME) is mainly related to partial 11βHSD2 deficiency associated with genetic variations and epigenetic modifications (first hit) and potential additive actions of endogenous or exogenous inhibitors (ie, glycyrrhetinic acid-like factors [GALFS]) and other factors (ie, age, high sodium intake) (second hit). Subjects with NC-AME are characterized by a high F/E ratio, low E levels, normal to elevated blood pressure, low plasma renin and increased urinary potassium excretion. NC-AME condition should benefit from low-sodium and potassium diet recommendations and monotherapy with MR antagonists.

CONCLUSION

NC-AME has a higher prevalence and a milder phenotypical spectrum than AME. NC-AME etiology is associated to a first hit (gene and epigene level) and an additive second hit. NC-AME subjects are candidates to be treated with MR antagonists aimed to improve blood pressure, end-organ damage, and modulate the renin levels.

Combination of Chronic Alcohol Consumption and High-Salt Intake Elicits Gut Microbial Alterations and Liver Steatosis in Mice

Alcohol is a globally well-established cause of fatty liver disease (FLD). Increased salt consumption is associated with an increased prevalence of adipocyte hypertrophy and liver injury. In this study, high dietary salt potentiated chronic alcohol-induced hepatic damage. We explored the physiological mechanism of alcoholic FLD in the gastrointestinal tract. Male C57BL/6J mice (8-week-old) were fed a high-salt diet (HSD; 4% NaCl) with or without chronic ethanol (CE) for 1 month. The fecal microbiota, serum biochemical indices, intestinal permeability, level of liver damage, and liver mitochondria were evaluated. The HSD, CE, and their combination (HSDE) significantly changed the gut microbiota's structure, and the HSDE mice contained more probiotic species (e.g., Bifidobacterium and Lactobacillus). The serum aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels were increased, and the lipid was accumulated in the liver tissues in the CE, HSD, and HSDE groups, which indicated liver damage, especially in the HSDE group. The increased intestinal permeability and mitochondrial dysfunction in the liver cells caused greater injury in the HSDE group than in the other groups. Thus, consuming HSD with alcohol contributes to FLD development and progression.

Targeting the Gut Microbiota to Investigate the Mechanism of Lactulose in Negating the Effects of a High-Salt Diet on Hypertension

SCOPE

High-salt diets (HSDs) are widely considered to cause health problems such as gut microecological imbalances, constipation, and hypertension. This study explores how lactulose as a safe molecule can stimulate bodily responses to alleviate salt-sensitive hypertension by regulating the gut microbiotas of HSD-fed mice.

METHODS AND RESULTS

After 4 weeks, the blood pressures of mice fed a high-salt plus lactulose diet (HSLD) are significantly lower than those of the HSD-fed mice. The HSD increases the abundances of Alistipes and Ruminococcaceae_UCG_009 and reduced the abundance of Lactobacillus in the gut, while lactulose supplementation increases the abundances of Bifidobacterium, Alloprevotella, and Subdoligranulum. Fecal metabolic profiling shows significant increases in metabolites involved in ATP-binding cassette transporter pathways, and tryptophan metabolism is significantly reduced in the HSLD group compared with the HSD group. Lactulose maintains the intestinal microenvironmental health in the HSD-fed mice by improving glycolipid metabolism, decreasing the small intestinal interleukin-17a (IL-17a) and interleukin-22 (IL-22) mRNA levels and serum IL-17a and IL-22 levels, relieving constipation, increasing fecal sodium, and reducing intestinal permeability.

CONCLUSION

Lactulose negates salt-sensitive hypertension. Regulating the gut microbiota is a potential treatment for salt-sensitive hypertension.

Renal and Blood Pressure Response to a High-Salt Diet in Mice With Reduced Global Expression of the Glucocorticoid Receptor

Salt-sensitive hypertension is common in glucocorticoid excess. Glucocorticoid resistance also presents with hypercortisolemia and hypertension but the relationship between salt intake and blood pressure (BP) is not well defined. GR^βgeo/+ mice have global glucocorticoid receptor (GR) haploinsufficiency and increased BP. Here we examined the effect of high salt diet on BP, salt excretion and renal blood flow in GR^βgeo/+mice. Basal BP was ∼10 mmHg higher in male GR^βgeo/+ mice than in GR^+/+ littermates. This modest increase was amplified by ∼10 mmHg following a high-salt diet in GR^βgeo/+ mice. High salt reduced urinary aldosterone excretion but increased renal mineralocorticoid receptor expression in both genotypes. Corticosterone, and to a lesser extent deoxycorticosterone, excretion was increased in GR^βgeo/+ mice following a high-salt challenge, consistent with enhanced 24 h production. GR^+/+ mice increased fractional sodium excretion and reduced renal vascular resistance during the high salt challenge, retaining neutral sodium balance. In contrast, sodium excretion and renal vascular resistance did not adapt to high salt in GR^βgeo/+ mice, resulting in transient sodium retention and sustained hypertension. With high-salt diet, Slc12a3 and Scnn1a mRNAs were higher in GR^βgeo/+ than controls, and this was reflected in an exaggerated natriuretic response to thiazide and benzamil, inhibitors of NCC and ENaC, respectively. Reduction in GR expression causes salt-sensitivity and an adaptive failure of the renal vasculature and tubule, most likely reflecting sustained mineralocorticoid receptor activation. This provides a mechanistic basis to understand the hypertension associated with loss-of-function polymorphisms in GR in the context of habitually high salt intake.

High-Salt Diet Induces IL-17-Dependent Gut Inflammation and Exacerbates Colitis in Mice

Excess intake of sodium is often associated with high risk for cardiovascular disease. More recently, some studies on the effects of high-salt diets (HSDs) have also demonstrated that they are able to activate Th17 cells and increase severity of autoimmune diseases. The purpose of the present study was to evaluate the effects of a diet supplemented with NaCl in the colonic mucosa at steady state and during inflammation. We showed that consumption of HSD by mice triggered a gut inflammatory reaction associated with IL-23 production, recruitment of neutrophils, and increased frequency of the IL-17-producing type 3 innate lymphoid cells (ILC3) in the colon. Moreover, gut inflammation was not observed in IL-17–/– mice but it was present, although at lower grade, in RAG^−/− mice suggesting that the inflammatory effects of HSD was dependent on IL-17 but only partially on Th17 cells. Expression of SGK1, a kinase involved in sodium homeostasis, increased 90 min after ingestion of 50% NaCl solution and decreased 3 weeks after HSD consumption. Colitis induced by oral administration of either dextran sodium sulfate or 2,4,6-trinitrobenzenesulfonic acid was exacerbated by HSD consumption and this effect was associated with increased frequencies of RORγt⁺ CD4⁺ T cells and neutrophils in the colon. Therefore, our results demonstrated that consumption of HSD per se triggered a histologically detectable inflammation in the colon and also exacerbated chemically induced models of colitis in mice by a mechanism dependent on IL-17 production most likely by both ILC3 and Th17 cells.

Role of Epithelium Sodium Channel in Bone Formation

Objective:

To review the recent developments in the mechanisms of epithelium sodium channels (ENaCs) induced bone formation and regulation.

Data Sources:

Studies written in English or Chinese were searched using Medline, PubMed and the index of Chinese-language literature with time restriction from 2005 to 2014. Keywords included ENaC, bone, bone formation, osteonecrosis, estrogen, and osteoporosis. Data from published articles about the structure of ENaC, mechanism of ENaC in bone formation in recent domestic and foreign literature were selected.

Study Selection:

Abstract and full text of all studies were required to obtain. Studies those were not accessible and those did not focus on the keywords were excluded.

Results:

ENaCs are tripolymer ion channels which are assembled from homologous α, β, and γ subunits. Crystal structure of ENaCs suggests that ENaC has a central ion-channel located in the central symmetry axis of the three subunits. ENaCs are protease sensitive channels whose iron-channel activity is regulated by the proteolytic reaction. Channel opening probability of ENaCs is regulated by proteinases, mechanical force, and shear stress. Several molecules are involved in regulation of ENaCs in bone formation, including nitride oxide synthases, voltage-sensitive calcium channels, and cyclooxygenase-2.

Conclusion:

The pathway of ENaC involved in shear stress has an effect on stimulating osteoblasts even bone formation by estrogen interference.

The importance of the gastrorenal axis in the control of body sodium homeostasis

NEW FINDINGS

What is the topic of this review? Sensing the amount of ingested sodium is one mechanism by which sodium balance is regulated. This review describes the role of gastrin in the cross-talk between the stomach and the kidney following the ingestion of sodium. What advances does it highlight? Neural mechanisms and several gut hormones, including cholecystokinin and uroguanylin, have been suggested to mediate the natriuresis after an oral sodium load. It is proposed that gastrin produced by G-cells via its receptor, cholecystokinin B receptor, interacts with renal D1 -like dopamine receptors to increase renal sodium excretion. Hypertension develops with chronically increased sodium intake when sodium that accumulates in the body can no longer be sequestered, extracellular fluid volume is expanded, and compensatory neural, hormonal and pressure-natriuresis mechanisms fail. Sensing the amount of ingested sodium, by the stomach, is one mechanism by which sodium balance is regulated. The natriuresis following the ingestion of a certain amount of sodium may be due to an enterokine, gastrin, secreted by G-cells in the stomach and duodenum and released into the circulation. Circulating gastrin levels are 10- to 20-fold higher than those for cholecystokinin. Of all the gut hormones circulating in the plasma, gastrin is the one that is reabsorbed to the greatest extent by renal tubules. Gastrin, via its receptor, the cholecystokinin type B receptor (CCKBR), is natriuretic in mammals, including humans, by inhibition of renal sodium transport. Germline deletion of gastrin (Gast) or Cckbr gene in mice causes salt-sensitive hypertension. Selective silencing of Gast in the stomach and duodenum impairs the ability to excrete an oral sodium load and also increases blood pressure. Thus, the gastrorenal axis, mediated by gastrin, can complement pronatriuretic hormones, such as dopamine, to increase sodium excretion after an oral sodium load. These studies in mice may be translatable to humans because the chromosomal loci of CCKBR and GAST are linked to human essential hypertension. Understanding the role of genes in the regulation of renal function and blood pressure may lead to the tailoring of antihypertensive treatment based on genetic make-up.

Mineralocorticoid Excess or Glucocorticoid Insufficiency: Renal and Metabolic Phenotypes in a Rat Hsd11b2 Knockout Model

Obesity and hypertension are 2 major health issues of the 21st century. The syndrome of apparent mineralocorticoid excess is caused by deficiency of 11β-hydroxysteroid dehydrogenase type 2 (Hsd11b2), which normally inactivates glucocorticoids, rendering the mineralocorticoid receptor aldosterone–specific. The metabolic consequences of Hsd11b2 knockout in the rat are investigated in parallel with electrolyte homeostasis. Hsd11b2 was knocked out, by pronuclear microinjection of targeted zinc-finger nuclease mRNAs, and 1 line was characterized for its response to renal and metabolic challenges. Plasma 11-dehydrocorticosterone was below detection thresholds, and Hsd11b2 protein was undetected by Western blot, indicating complete ablation. Homozygotes were 13% smaller than wild-type littermates, and were polydipsic and polyuric. Their kidneys, adrenals, and hearts were significantly enlarged, but mesenteric fat pads and liver were significantly smaller. On a 0.3% Na diet, mean arterial blood pressure was ≈65 mm Hg higher than controls but only 25 mm Hg higher on a 0.03% Na⁺ diet. Urinary Na/K ratio of homozygotes was similar to controls on 0.3% Na⁺ diet but urinary albumin and calcium were elevated. Corticosterone and aldosterone levels showed normal circadian variation on both a 0.3% and 0.03% Na⁺ diet, but plasma renin was suppressed in homozygotes on both diets. Plasma glucose responses to an oral glucose challenge were reduced despite low circulating insulin, indicating much greater sensitivity to insulin in homozygotes. The rat model reveals mechanisms linking electrolyte homeostasis and metabolic control through the restriction of Hsd11b1 substrate availability.

Inhibition of ENaC by endothelin-1

The amiloride-sensitive epithelial Na(+) channel (ENaC) is a key player in the regulation of Na(+) homeostasis. Its functional activity is under continuous control by a variety of signaling molecules, including bioactive peptides of endothelin family. Since ENaC dysfunction is causative for disturbances in total body Na(+) levels associated with the abnormal regulation of blood volume, blood pressure, and lung fluid balance, uncovering the molecular mechanisms of inhibitory modulation or inappropriate activation of ENaC is crucial for the successful treatment of a variety of human diseases including hypertension. The precise regulation of ENaC is particularly important for normal Na(+) and fluid homeostasis in organs where endothelins are known to act: the kidneys, lung, and colon. Inhibition of ENaC by endothelin-1 (ET-1) has been established in renal cells, and several molecular mechanisms of inhibition of ENaC by ET-1 are proposed and will be reviewed in this chapter.

Insulin, CCAAT/enhancer-binding proteins and lactate regulate the human 11β-hydroxysteroid dehydrogenase type 2 gene expression in colon cancer cell lines

11β-Hydroxysteroid dehydrogenases (11beta-HSD) modulate mineralocorticoid receptor transactivation by glucocorticoids and regulate access to the glucocorticoid receptor. The isozyme 11beta-HSD2 is selectively expressed in mineralocorticoid target tissues and its activity is reduced in various disease states with abnormal sodium retention and hypertension, including the apparent mineralocorticoid excess. As 50% of patients with essential hypertension are insulin resistant and hyperinsulinemic, we hypothesized that insulin downregulates the 11beta-HSD2 activity. In the present study we show that insulin reduced the 11beta-HSD2 activity in cancer colon cell lines (HCT116, SW620 and HT-29) at the transcriptional level, in a time and dose dependent manner. The downregulation was reversible and required new protein synthesis. Pathway analysis using mRNA profiling revealed that insulin treatment modified the expression of the transcription factor family C/EBPs (CCAAT/enhancer-binding proteins) but also of glycolysis related enzymes. Western blot and real time PCR confirmed an upregulation of C/EBP beta isoforms (LAP and LIP) with a more pronounced increase in the inhibitory isoform LIP. EMSA and reporter gene assays demonstrated the role of C/EBP beta isoforms in HSD11B2 gene expression regulation. In addition, secretion of lactate, a byproduct of glycolysis, was shown to mediate insulin-dependent HSD11B2 downregulation. In summary, we demonstrate that insulin downregulates HSD11B2 through increased LIP expression and augmented lactate secretion. Such mechanisms are of interest and potential significance for sodium reabsorption in the colon.

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.

Age-related changes in 11β-hydroxysteroid dehydrogenase type 2 activity in normotensive subjects

BACKGROUND

Impairment in 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) activity results in inefficient inactivation of cortisol to cortisone, and it can trigger hypertension through activation of the mineralocorticoid receptor. Information about age-related changes in 11β-HSD2 activity and its physiological consequences is scarce. Our aim was to investigate whether 11β-HSD2 activity is age dependent in normotensive subjects.

METHODS

We recruited 196 healthy, normotensive subjects. Of these, 93 were children (Group 1: aged 5-15 years), and 103 were adults who were divided according to their ages: Group 2: aged 30-41 years (n = 10); Group 3: aged 42-53 years (n = 72); and Group 4: aged 54-65 years (n = 21). Fasting serum cortisol, cortisone, aldosterone, and plasma renin activity (PRA) were measured. The 11β-HSD2 activity was estimated by the cortisol/cortisone ratio. The results were expressed as median (interquartile range (IQR)) values and compared using Kruskal-Wallis and Dunn's multiple-comparison tests.

RESULTS

As subject age increased, cortisol concentrations increased (Group 1 median = 8.6, IQR = 6.3-10.8 µg/dl; Group 4 median = 12.4, IQR = 10.7-14.7 µg/dl; P < 0.001), and cortisone concentrations showed a gradual decrease (Group 2 median = 4.0, IQR = 3.3-4.2 µg/dl; Group 4 median =2.8, IQR = 2.6-3.3 µg/dl; P < 0.01). As a consequence, the cortisol/cortisone ratio was higher in the oldest subjects (Group 4) than in the subjects from the other 3 groups; the ratios from Group 4 to Group 1 were 4.4 (IQR = 3.7-5.1) µg/dl, 3.3 (IQR = 2.7-3.8) µg/dl, 2.5 (IQR = 2.3-3.8) µg/dl, and 2.7 (IQR = 2.1-3.4) µg/dl, respectively (P < 0.01). The PRA decreased with age. Blood pressure levels increased with age but stayed within the normal range.

CONCLUSIONS

Cortisol and the cortisol/cortisone ratio increased with age, but cortisone decreased, suggesting a decrease in 11β-HSD2 activity. These results suggest that the cortisol-mediated activation of the mineralocorticoid receptor may explain the blood pressure increase in elderly subjects.

Long-term space flight simulation reveals infradian rhythmicity in human Na(+) balance

The steady-state concept of Na(+) homeostasis, based on short-term investigations of responses to high salt intake, maintains that dietary Na(+) is rapidly eliminated into urine, thereby achieving constant total-body Na(+) and water content. We introduced the reverse experimental approach by fixing salt intake of men participating in space flight simulations at 12 g, 9 g, and 6 g/day for months and tested for the predicted constancy in urinary excretion and total-body Na(+) content. At constant salt intake, daily Na(+) excretion exhibited aldosterone-dependent, weekly (circaseptan) rhythms, resulting in periodic Na(+) storage. Changes in total-body Na(+) (±200-400 mmol) exhibited longer infradian rhythm periods (about monthly and longer period lengths) without parallel changes in body weight and extracellular water and were directly related to urinary aldosterone excretion and inversely to urinary cortisol, suggesting rhythmic hormonal control. Our findings define rhythmic Na(+) excretory and retention patterns independent of blood pressure or body water, which occur independent of salt intake.