Modulation of renal calcium handling by 11 beta-hydroxysteroid dehydrogenase type 2

Apparent mineralocorticoid excess in Israel: a case series and literature review

BACKGROUND AND OBJECTIVE

Apparent mineralocorticoid excess (AME) syndrome is an ultra-rare autosomal-recessive tubulopathy, caused by mutations in HSD11B2, leading to excessive activation of the kidney mineralocorticoid receptor, and characterized by early-onset low-renin hypertension, hypokalemia, and risk of chronic kidney disease (CKD). To date, most reports included few patients, and none described patients from Israel. We aimed to describe AME patients from Israel and to review the relevant literature.

DESIGN

Retrospective cohort study.

METHODS

Clinical, laboratory, and molecular data from patients' records were collected.

RESULTS

Five patients presented at early childhood with normal estimated glomerular filtration rate (eGFR), while 2 patients presented during late childhood with CKD. Molecular analysis revealed 2 novel homozygous mutations in HSD11B2. All patients presented with severe hypertension and hypokalemia. While all patients developed nephrocalcinosis, only 1 showed hypercalciuria. All individuals were managed with potassium supplements, mineralocorticoid receptor antagonists, and various antihypertensive medications. One patient survived cardiac arrest secondary to severe hyperkalemia. At last follow-up, those 5 patients who presented early exhibited normal eGFR and near-normal blood pressure, but 2 have hypertension complications. The 2 patients who presented with CKD progressed to end-stage kidney disease (ESKD) necessitating dialysis and kidney transplantation.

CONCLUSIONS

In this 11-year follow-up report of 2 Israeli families with AME, patients who presented early maintained long-term normal kidney function, while those who presented late progressed to ESKD. Nevertheless, despite early diagnosis and management, AME is commonly associated with serious complications of the disease or its treatment.

Assessment of Vitamin D Metabolism in Patients with Cushing's Disease in Response to 150,000 IU Cholecalciferol Treatment

In this study we aimed to assess vitamin D metabolism in patients with Cushing’s disease (CD) compared to healthy individuals in the setting of bolus cholecalciferol treatment. The study group included 30 adults with active CD and the control group included 30 apparently healthy adults with similar age, sex and BMI. All participants received a single dose (150,000 IU) of cholecalciferol aqueous solution orally. Laboratory assessments including serum vitamin D metabolites (25(OH)D₃, 25(OH)D₂, 1,25(OH)₂D₃, 3-epi-25(OH)D₃ and 24,25(OH)₂D₃), free 25(OH)D, vitamin D-binding protein (DBP) and parathyroid hormone (PTH) as well as serum and urine biochemical parameters were performed before the intake and on Days 1, 3 and 7 after the administration. All data were analyzed with non-parametric statistics. Patients with CD had similar to healthy controls 25(OH)D₃ levels (p > 0.05) and higher 25(OH)D₃/24,25(OH)₂D₃ ratios (p < 0.05) throughout the study. They also had lower baseline free 25(OH)D levels (p < 0.05) despite similar DBP levels (p > 0.05) and lower albumin levels (p < 0.05); 24-h urinary free cortisol showed significant correlation with baseline 25(OH)D₃/24,25(OH)₂D₃ ratio (r = 0.36, p < 0.05). The increase in 25(OH)D₃ after cholecalciferol intake was similar in obese and non-obese states and lacked correlation with BMI (p > 0.05) among patients with CD, as opposed to the control group. Overall, patients with CD have a consistently higher 25(OH)D₃/24,25(OH)₂D₃ ratio, which is indicative of a decrease in 24-hydroxylase activity. This altered activity of the principal vitamin D catabolism might influence the effectiveness of cholecalciferol treatment. The observed difference in baseline free 25(OH)D levels is not entirely clear and requires further study.

Calcium and phosphate homeostasis in dogs with newly diagnosed naturally occurring hypercortisolism

Background

Hypercortisolism affects calcium and phosphate metabolism in dogs; however, the exact mechanisms are not completely understood.

Objectives

To evaluate circulating concentrations of whole parathormone (wPTH), 25‐hydroxyvitamin D (25‐(OH)D), calcitriol, and fibroblast growth factor‐23 (FGF‐23) in dogs with naturally occurring hypercortisolism (NOHC) and healthy dogs, and their association with calcium and phosphate homeostasis.

Animals

Twenty‐three client‐owned dogs with NOHC, and 12 client or staff‐owned healthy dogs.

Methods

Prospective cross‐sectional study. The circulating concentrations of total calcium, ionized calcium (iCa), phosphate, wPTH, 25‐(OH)D, calcitriol and FGF‐23, and the urinary fractional excretion of phosphate (FEP) and calcium (FECa) were compared between dogs with NOHC before treatment and healthy dogs.

Results

Dogs with NOHC had higher mean serum phosphate concentrations (4.81 mg/dL, SD ± 0.71 vs 3.86 mg/dL, SD ± 0.60; P < .001), median FECa (0.43%, range, 0.03‐2.44 vs 0.15%, range, 0.06‐0.35; P = .005), and median serum wPTH concentrations (54.6 pg/mL, range, 23.7‐490 vs 24.6 pg/mL, range, 5.5‐56.4; P = .003) as compared to the controls. Circulating concentrations of total calcium, iCa, and calcitriol and the FEP did not differ between groups, whereas the serum 25‐(OH)D concentrations were lower in dogs with NOHC as compared to the controls (70.2 pg/mL, SD ± 42.3 vs 106.3 pg/mL, SD ± 35.3; P = .02). The dogs with NOHC had lower plasma FGF‐23 concentrations than controls (316.6 pg/mL, range, 120.8‐575.6 vs 448.7 pg/mL, range, 244.8‐753; P = .03).

Conclusions and Clinical Importance

Urine loss of calcium and hyperphosphatemia could contribute to the adrenal secondary hyperparathyroidism.

Urinary excretion of calcium and phosphate in dogs with pituitary-dependent hypercortisolism: case control study in 499 dogs

Pituitary-dependent hypercortisolism (PDH) in dogs is frequently associated with high serum phosphate and parathormone concentrations which are in turn associated with prognosis and clinical presentation. The pathogenesis of such abnormalities remains unknown. The aim of the present study was to evaluate the serum and urinary concentrations and the urinary fractional excretion of phosphate and calcium in dogs with PDH. Medical records of newly diagnosed PDH dogs before treatment from one referral centre were retrospectively evaluated. One clinically normal and one sick dog for each dog with PDH were included as controls. One hundred and sixty-seven dogs with PDH were included. The serum phosphate concentration in PDH dogs was significantly (P<0.0001) higher compared with clinically normal control dogs (CNDs) and sick control dogs (SCDs). The serum calcium concentration in PDH dogs was significantly higher compared with SCDs but not different compared with CNDs. Urinary fractional excretion of phosphate in PDH dogs was significantly lower compared with CNDs and SCDs. Urinary fractional excretion of calcium in PDH dogs was significantly higher compared with CNDs and SCDs. In conclusion, PDH dogs have lower phosphaturia and higher calciuria compared with control dogs. These findings suggest that, at least in part, high serum phosphate concentrations are related to the renal retention of phosphate.

The consequences of pediatric renal transplantation on bone metabolism and growth

PURPOSE OF REVIEW

During childhood, growth retardation, decreased final height and renal osteodystrophy are common complications of chronic kidney disease (CKD). These problems remain present in patients undergoing renal transplantation, even though steroid-sparing strategies are more widely used. In this context, achieving normal height and growth in children after transplantation is a crucial issue for both quality of life and self-esteem. The aim of this review is to provide an overview of pathophysiology of CKD-mineral bone disorder (MBD) in children undergoing renal transplantation and to propose keypoints for its daily management.

RECENT FINDINGS

In adults, calcimimetics are effective for posttransplant hyperparathyroidism, but data are missing in the pediatric population. Fibroblast growth factor 23 levels are associated with increased risk of rejection, but the underlying mechanisms remain unclear. A recent meta-analysis also demonstrated the effectiveness of rhGH therapy in short transplanted children.

SUMMARY

In 2013, the daily clinical management of CKD-MBD in transplanted children should still focus on simple objectives: to optimize renal function, to develop and promote steroid-sparing strategies, to provide optimal nutritional support to maximize final height and avoid bone deformations, to equilibrate calcium/phosphate metabolism so as to provide acceptable bone quality and cardiovascular status, to correct all metabolic and clinical abnormalities that can worsen both bone and growth (mainly metabolic acidosis, anemia and malnutrition), promote good lifestyle habits (adequate calcium intake, regular physical activity, no sodas consumption, no tobacco exposure) and eventually to correct native vitamin D deficiency (target of 25-vitamin D >75 nmol/l).

Eating disorders should be considered in the differential diagnosis of patients presenting with acute kidney injury and electrolyte derangement

We present a case of a 40-year-old woman with a history of ongoing anorexia nervosa and bulimia nervosa who has required multiple admissions to hospital for management of acute kidney injury (AKI) and electrolyte derangement. This case is of interest as recent studies have highlighted the significant prevalence of disordered eating and the major public health implications this may have. We discuss the unusual finding of hypercalcaemia in this case and address the investigation and management of AKI and electrolyte disturbance in a patient with anorexia and bulimia.

[Mineral and bone disorders in renal transplantation]

The deregulation of bone and mineral metabolism during chronic kidney disease (CKD) is a daily challenge for physicians, its management aiming at decreasing the risk of both fractures and vascular calcifications. Renal transplantation in the context of CKD, with pre-existing renal osteodystrophy as well as nutritional impairment, chronic inflammation, hypogonadism and corticosteroids exposure, represents a major risk factor for bone impairment in the post-transplant period. The aim of this review is therefore to provide an update on the pathophysiology of mineral and bone disorders after renal transplantation.

Chronic stress and calcium oxalate stone disease: influence on blood cortisol and urine composition

OBJECTIVE

To evaluate the influence of chronic stress (CS) on urine composition of calcium oxalate (CaOx) stone patients and controls.

METHODS

This case-control study enrolled 128 patients during a period of 20 months. The cases were CaOx stone formers with a recent stone episode. Controls were matched by sex and age. Dimensions of CS were evaluated in cases and controls by validated self-report questionnaires measuring stressful life events, perceived stress, anxiety, depression, burnout, and satisfaction with life. Blood and urine samples were collected to determine cortisol levels and urinary composition.

RESULTS

More relations between CS dimensions and blood and urine parameters were observed in cases than in controls. In cases, the blood cortisol level was related positively with the number of stressful life events (P = .03), intensity of these events (P = .04), and anxiety (P = .04). In addition, urinary magnesium (P = .03) and pyrophosphate (P = .05) levels were positively related with satisfaction with life and burnout, respectively. In contrast, urinary magnesium levels were negatively related with perceived stress (P = .01), anxiety (P = .016), and depression (P = .03). In controls, the number of stressful life events and the intensity of stressful life events was related positively with magnesium (P = .06, P = .02) levels and negatively with blood cortisol levels (P = .03, P = .004).

CONCLUSION

Based on the variation between cases and controls in relations between CS dimensions and biochemical parameters, we hypothesize that CS may trigger a differential biological response in CaOx stone formers and controls, which in turn may promote or protect against CaOx stone formation.

Primary male osteoporosis is associated with enhanced glucocorticoid availability

OBJECTIVE

While systemic glucocorticoids compromise bone metabolism, altered intracellular cortisol availability may also contribute to the pathogenesis of primary male osteoporosis (MO). The objective of this study was to assess whether intracellular cortisol availability is increased in MO due to a distorted local cortisol metabolism.

METHODS

Forty-one patients with MO were compared with age- and BMI-matched non-osteoporotic subjects after excluding overt systemic hypercortisolism (N = 41). Cortisol, cortisone and the respective tetrahydro-, 5α-tetrahydro- and total cortisol metabolites were analysed by GC-MS in 24 h urine. Apparent 11β-hydroxysteroid dehydrogenase (11β-HSD) enzyme activities, excretion of cortisol metabolites and calcium, and fractional urinary calcium excretion were assessed and related to BMD.

RESULTS

Fractional and total urinary calcium excretion negatively correlated with BMD at all (P < 0.05) and at three of five (P < 0.05) measurement sites, respectively. While systemic cortisol was unchanged, apparent 11β-HSD enzyme activity in MO patients (P < 0.01) suggested increased intracellular cortisol availability. Total and fractional urinary calcium excretion was higher, with apparent 11β-HSD enzyme activities consistent with an enhanced intracellular cortisol availability (P < 0.05).

CONCLUSION

Apparent 11β-HSD enzyme activities consistent with increased intracellular cortisol availability correlated with urinary calcium loss and reduced bone mineral density in MO. The changes in 11β-HSD activity were associated with both the fractional calcium excretion, suggesting altered renal calcium handling, and the absolute urinary calcium excretion. Both mechanisms could result in a marked bone calcium deficiency if insufficiently compensated for by intestinal calcium uptake.

Syndrome of inappropriate ADH secretion and severe osteoporosis

OBJECTIVE

Recent studies indicate an association between hyponatremia and osteoporosis. We report a clinical case that supports this statement.

CASE REPORT

A 36-yr-old man was diagnosed with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) at the age of 22. In the years that followed, sodium levels in the blood remained low from 111-130 mmol/liter (137-144). At the age of 34, he was diagnosed with osteoporosis after a magnetic resonance imaging scan showed moderate compression fractures at Th9-11 and L2. A dual energy x-ray absorptiometry scan showed a Z-score of -3.9 at the lumbar spine (L3-L4) and a Z-score of -1.3 in the total hip. He had no other known risk factors for osteoporosis. Urinary excretion of calcium and sodium were elevated. Plasma vasopressin level was inappropriately elevated. One year after treatment with 5-mg zoledronic acid, there has been no significant change in the bone mineral density in the lumbar spine and a small increase in bone mineral density in the total hip. The symptoms from SIADH have not changed.

CONCLUSION

The case illustrates that severe idiopathic SIADH and chronic hyponatremia can have severe side effects on bone metabolism and can lead to secondary osteoporosis. We support the recommendation that patients with chronic SIADH should be screened for osteoporosis and suggest that early bone protective treatment should be considered to reduce or delay osteoporosis onset.

Subchronic toxicity of Sipjeondaebo-tang (SDT) in Sprague-Dawley rats

Sipjeondaebo-tang (SDT, Juzen-taiho-to in Japanese), a traditional Korean herbal medicine, is used as a supplemental treatment for the adverse effects of chemotherapy, radiation therapy, and surgical treatment. However, limited information is available about the long-term safety of SDT. Therefore, we evaluated the potential adverse effects of SDT in Sprague-Dawley rats over a period of 13-weeks. The SDT was administered once daily by gavage to male and female rats at dose levels of 0, 250, 500, 1000 and 2000 mg/kg/day for 13 weeks. The SDT treatment did not result in any toxicologically significant changes in mortality, clinical signs, body weights, food and water consumption, ophthalmoscopy, urinalysis, hematology, serum biochemistry, gross findings, organ weights, histopathology, estrus cycle, serum testosterone levels and sperm analysis. We concluded that the 13-week repeated oral administration of SDT did not cause any adverse effects in rats at dose levels of ≤ 2000 mg/kg/day. Under these experimental conditions, the no-observed-adverse-effect level (NOAEL) was more than 2000 mg/kg/day for both genders. Here, we demonstrated the safety of a 13-week repeated oral dose and considered that it is a safe herbal medicine for human consumption.

Cushing's syndrome, glucocorticoids and the kidney

Glucocorticoids (GCs) affect renal development and function in fetal and mature kidneys both indirectly, by influencing the cardiovascular system, and directly, by their effects on glomerular and tubular function. Excess GCs due to endogenous GC overproduction in Cushing's syndrome or exogenous GC administration plays a pivotal role in hypertension and causes increased cardiac output, total peripheral resistance and renal blood flow. Glucocorticoids increase renal vascular resistance (RVR) in some species and experimental settings and decrease RVR in others. Short term administration of adrenocorticotrophic hormone or GCs causes an increased glomerular filtration rate (GFR) in humans, rats, sheep and dogs. Interestingly, chronic exposure may cause a decreased GFR in combination with a higher cardiovascular risk in human patients with Cushing's syndrome. Glomerular dysfunction leads to proteinuria and albuminuria in canine and human Cushing's patients, and some cases also show histological evidence of glomerulosclerosis. Tubular dysfunction is reflected by an impaired urinary concentrating ability and disturbed electrolyte handling, which can potentially result in increased sodium reabsorption, hypercalciuria and urolithiasis. Conversely, chronic kidney disease can also alter GC metabolism. More research needs to be performed to further evaluate the renal consequences of Cushing's syndrome because of its implications for therapeutic aspects as well as the general well-being of the patient. Because there is a high incidence of Cushing's syndrome in canines, which is similar to the syndrome in humans, dogs are an interesting animal model to investigate the link between hypercortisolism and renal function.

A possible involvement of 3-monoglucuronyl-glycyrrhetinic acid, a metabolite of glycyrrhizin (GL), in GL-induced pseudoaldosteronism

Glycyrrhizin (GL), a major ingredient of Glycyrrhiza Radix (licorice), is widely used to treat various disorders or as a sweetener. It is also known that GL occasionally induces pseudoaldosteronism. It is conceivable that the active form of GL in pseudoaldosteronism induction is glycyrrhetinic acid (GA). Although it is reported that 3-monoglucuronyl-glycyrrhetinic acid (3MGA) is detectable specifically in the plasma of patients with GL-induced hypokalemia, pharmacokinetics and a hypokalemia induction mode of action for 3MGA have not been clarified. We investigated the toxicokinetics of GL, GA and 3MGA in a single or multiple oral administration of GL. The results suggested that higher blood concentrations of 3MGA were maintained by the multiple administration compared to the single dose, whereas the concentrations of GA and GL showed no difference. We injected 3MGA intravenously and found that it can decrease the plasma potassium level (PPL) in vivo. It is clinically recommended to avoid a combination treatment of GL and furosemide. While treatment with a low dosage of furosemide had no effect on PPL, the multiple administration of GL and furosemide markedly decreased PPL compared to the effect of administering GL alone. In the single dosage regime, there was no difference between PPL after the combination treatment and after administering GL alone. Collectively, these findings suggested that accumulation of 3MGA may be involved in the pathogenesis of pseudoaldosteronism induced by chronic GL treatment.

Apparent Mineralocorticoid Excess: Report of Six New Cases and Extensive Personal Experience

In mineralocorticoid target tissues such as the cortical collecting duct in the kidney, the enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) is responsible for the peripheral inactivation of cortisol to cortisone, thereby protecting the mineralocorticoid receptor from inappropriate activation by cortisol. Mutations in the HSD11B2 gene cause the syndrome of apparent mineralocorticoid excess, an autosomal recessive form of inherited hypertension in which cortisol acts as a potent mineralocorticoid. Herein are described six new families with mutations in the HSD11B2 gene causing hypokalemic hypertension, with low plasma aldosterone and low renin levels in affected individuals, indicating mineralocorticoid hypertension. Profiling of urinary steroid metabolites showed decreased cortisol inactivation, with urinary tetrahydrocortisol and tetrahydrocortisone ratio (THF + 5alphaTHF)/THE ranging 2.4 to 40 and nearly absent urinary free cortisone in all but one case. Genetic analysis of the HSD11B2 gene from these patients with apparent mineralocorticoid excess revealed distinct homozygous point mutations in four families, a compound heterozygous mutation in one family, and a large 23-bp exonic insert with frameshift and disruption of the amino acid sequence in another family. Expression studies of mutants that were expressed in HEK-293 cells showed marked reduction or abolition of 11betaHSD2 enzymatic activity. These cases are reviewed along with previous ones from the authors' extensive personal experience to highlight the importance of 11betaHSD2 in the understanding of a new biologic principle in hormone action, demonstrating that local metabolism of the glucocorticoid hormones into inactive derivatives by the enzyme 11betaHSD2 is one of the mechanisms that intervene to allow specific aldosterone regulatory effects.

Impaired 11 beta-hydroxysteroid dehydrogenase contributes to renal sodium avidity in cirrhosis: hypothesis or fact?

Exaggerated renal sodium retention with concomitant potassium loss is a hallmark of cirrhosis and contributes to the accumulation of fluid as ascites, pleural effusion, or edema. This apparent mineralocorticoid effect is only partially explained by increased aldosterone concentrations. I present evidence supporting the hypothesis that cortisol confers mineralocorticoid action in cirrhosis. The underlying molecular pathology for this mineralocorticoid receptor (MR) activation by cortisol is a reduced activity of the 11 beta-hydroxysteroid dehydrogenase type 2, an enzyme protecting the MR from promiscuous activation by cortisol in healthy mammalians.

Use of 11alpha-deuterium labeled cortisol as a tracer for assessing reduced 11beta-HSD2 activity in vivo following glycyrrhetinic acid ingestion in a human subject

This study describes an oral administration of 5 mg of [1,2,4,19-13C4,11alpha-2H]cortisol (cortisol-13C4,2H1) to a human subject performed on two separate occasions, one with cortisol-13C4,2H1 alone and the other with cortisol-13C4,2H1 plus 130 mg per day of glycyrrhetinic acid for 6 days. The stable isotope methodology employed allowed for the evaluation of the individual in vivo activities of the two isozymes of 11beta-hydroxysteroid dehydrogenase (11beta-HSD), 11beta-HSD1 and 11beta-HSD2, and to demonstrate the sensitivity of changes in cortisol elimination half-life for detecting inhibition of 11beta-HSD2 activity induced with glycyrrhetinic acid. The kinetic analysis associated with the loss of 11alpha-2H during the conversion of cortisol-13C4,2H1 to cortisone-13C4 by 11beta-HSD2 clearly indicated reduced 11beta-HSD2 activity with glycyrrhetinic acid ingestion, as observed by an increase in the elimination half-life of cortisol-13C4,2H1. The elimination half-life of cortisol-13C4,2H1 provided sensitive in vivo measures of 11beta-HSD2 activity and was more sensitive for detecting changes in renal 11beta-HSD2 activity than the measurement of the urinary ratio of free cortisol and free cortisone (UFF/UFE). The 2H-labeling in the 11alpha-position of cortisol served as an appropriate tracer for assessing the reduced 11beta-HSD2 activity in vivo induced by glycyrrhetinic acid.

A case of pseudoaldosteronism, accompanied with hypocalcemia and exaggerated ACTH response

Glycyrrhizic acid (GA) inhibits the activity of 11beta-hydroxysteroid dehydrogenase type 2 in the kidney, with the resulting increase in intrarenal cortisol concentration leading to hypertension and suppression of the renin-aldosterone system. In this paper we describe an interesting case of pseudoaldosteronism, associated with hypocalcemia and an exaggerated ACTH response. A 72-year-old woman was referred to our department for further evaluation of hypokalemia and hypocalcemia. The patient had been taking GA (150 mg/day) for the previous year for treatment of liver damage. Plasma renin activity and aldosterone concentration were both within lower normal limits. Urinary excretion of potassium and calcium was within the upper limit of the normal range and increased with administration of supplements. Plasma ACTH levels increased markedly in response to an intravenous injection of CRH. Cessation of GA and the potassium and calcium supplements on admission, led to a gradual normalization of serum potassium and calcium levels and blood pressure. The hypocalcaemia in our patient was related to decreased tubular reabsorption of calcium as a consequence of renal corticoid excess. It is possible that an increase in the number of CRH receptors in the pituitary following GA treatment caused the exaggerated ACTH response in association with pseudoaldosteronism. The existence of hypocalcemia and an exaggerated ACTH response should be observed carefully when managing pseudoaldosteronism.

Cortisol and the renal handling of electrolytes: role in glucocorticoid-induced hypertension and bone disease

Hypertension and osteoporosis are characteristic clinical features in patients with Cushing's syndrome or in those on glucocorticoid (GC) treatment. These two distinct complications of GC excess share one common denominator: an abnormal handling of cations, sodium (Na(+)) and calcium (Ca(2+)), either primarily or in part by the kidney tubule. The principal mechanism of GC-induced hypertension is overstimulation of the non-selective mineralocorticoid receptor (MR), resulting in renal Na(+) retention, volume expansion and finally to an increase in blood pressure. In mineralocorticoid target organs, such as the kidney, the MR is protected from GC occupation by the enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2), a gate-keeping enzyme, which converts cortisol to receptor-inactive cortisone. This enzyme allows aldosterone to be the physiological agonist of the MR despite significantly higher circulating levels of cortisol. Kinetic properties of 11betaHSD2 suggest that saturability of this enzyme can already be achieved at high-normal physiological plasma cortisol levels, thereby leading to ovestimualtion of the MR by cortisol in states of GC excess. The mechanisms of GC action on bone turnover are more complex. GCs increase bone resorption, inhibit bone formation and have an indirect action on bone by decreasing intestinal Ca(2+) absorption, but also inducing a sustained renal Ca(2+) excretion. The latter appears to be mediated through stimulation of the MR by GC. The prevention and treatment of GC-induced hypertension and osteoporosis include the use of the minimal effective dose of GC, some general measures, and the use of some specific drugs. Modulation of renal Na(+) and Ca(2+) excretion with some, but not all, diuretics represents an important specific (for hypertension) or supportive (for bone disease) therapeutic intervention.

Forms of mineralocorticoid hypertension

Hypertension with hypokalemia, metabolic alkalosis, and suppressed plasma renin activity defines mineralocorticoid hypertension. Mineralocorticoid hypertension is the consequence of an overactivity of the epithelial sodium channel expressed at the apical membrane of renal cells in the distal nephron. This is usually the case when the mineralocorticoid receptor is activated by its physiologic substrate aldosterone. The best known form of mineralocorticoid hypertension is an aldosterone-producing adrenal tumor leading to primary aldosteronism. Primary aldosteronism can also be caused by unilateral or bilateral adrenal hyperplasia and rarely adrenal carcinoma. Interestingly, most of the inherited monogenic disorders associated with hypertension involve an excessive activation of the mineralocorticoid axis. In some of these disorders, mineralocorticoid hypertension results from activation of the mineralocorticoid receptor by other steroids (cortisol, deoxycorticosterone), by primary activation of the receptor itself, or by constitutive overactivity of the renal epithelial sodium channel. The present review addresses the physiology and significance of the key players of the mineralocorticoid axis, placing emphasis on the conditions leading to mineralocorticoid hypertension.