Renal handling of calcium and phosphate during mineralocorticoid administration in normal subjects

Vertebral fractures assessed with dual-energy X-ray absorptiometry in patients with Addison's disease on glucocorticoid and mineralocorticoid replacement therapy

PURPOSE

to assess bone damage and metabolic abnormalities in patients with Addison's disease given replacement doses of glucocorticoids and mineralocorticoids.

METHODS

A total of 87 patients and 81 age-matched and sex-matched healthy controls were studied. The following parameters were measured: urinary cortisol, serum calcium, phosphorus, creatinine, 24-h urinary calcium excretion, bone alkaline phosphatase, parathyroid hormone, serum CrossLaps, 25 hydroxyvitamin D, and 1,25 dihydroxyvitamin D. Clear vertebral images were obtained with dual-energy X-ray absorptiometry in 61 Addison's disease patients and 47 controls and assessed using Genant's classification.

RESULTS

Nineteen Addison's disease patients (31.1%) had at least one morphometric vertebral fracture, as opposed to six controls (12.8%, odds ratio 3.09, 95% confidence interval 1.12-8.52). There were no significant differences in bone mineral density parameters at any site between patients and controls. In Addison's disease patients, there was a positive correlation between urinary cortisol and urinary calcium excretion. Patients with fractures had a longer history of disease than those without fractures. Patients taking fludrocortisone had a higher bone mineral density than untreated patients at all sites except the lumbar spine.

CONCLUSIONS

Addison's disease patients have more fragile bones irrespective of any decrease in bone mineral density. Supra-physiological doses of glucocorticoids and longer-standing disease (with a consequently higher glucocorticoid intake) might be the main causes behind patients' increased bone fragility. Associated mineralocorticoid treatment seems to have a protective effect on bone mineral density.

Salt, Aldosterone, and Parathyroid Hormone: What Is the Relevance for Organ Damage?

Structured interventions on lifestyle have been suggested as a cost-effective strategy for prevention of cardiovascular disease. Epidemiologic studies demonstrate that dietary salt restriction effectively decreases blood pressure, but its influence on cardiovascular morbidity and mortality is still under debate. Evidence gathered from studies conducted in patients with primary aldosteronism, essential hypertension, or heart failure demonstrates that long-term exposure to elevated aldosterone results in cardiac structural and functional changes that are independent of blood pressure. Animal experiments and initial clinical studies indicate that aldosterone damages the heart only in the context of an inappropriately elevated salt status. Recent evidence suggests that aldosterone might functionally interact with the parathyroid hormone and thereby affect calcium homeostasis with important sequelae for bone mineral density and strength. The interaction between aldosterone and parathyroid hormone might have implications also for the heart. Elevated dietary salt is associated on the one hand with increased urinary calcium excretion and, on the other hand, could facilitate the interaction between aldosterone and parathyroid hormone at the cellular level. This review summarizes the evidence supporting the contribution of salt and aldosterone to cardiovascular disease and the possible cardiac and skeletal consequences of the mutual interplay between aldosterone, parathyroid hormone, and salt.

Aldosterone signaling and soluble adenylyl cyclase-a nexus for the kidney and vascular endothelium

The steroid hormone aldosterone regulates the reabsorption of water and ions in the kidney and plays a central role in blood pressure regulation and homeostasis. In recent years, the vascular endothelium has been established as an important aldosterone target organ with major implications in renal and cardiovascular health and disease. Different lines of evidence suggest that the calcium- and bicarbonate-activated soluble adenylyl cyclase (sAC) is a novel mediator of aldosterone signaling in both the kidney and vascular endothelium. This review summarizes our current understanding of the molecular mechanisms of sAC gene expression regulation in the kidney and vascular endothelium and outlines the potential clinical implications of sAC in chronic kidney disease and cardiovascular disease. This review is part of a special issue entitled: The role of soluble adenylyl cyclase in health and disease. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Aldosterone and parathyroid hormone interactions as mediators of metabolic and cardiovascular disease

Inappropriate aldosterone and parathyroid hormone (PTH) secretion is strongly linked with development and progression of cardiovascular (CV) disease. Accumulating evidence suggests a bidirectional interplay between parathyroid hormone and aldosterone. This interaction may lead to a disproportionally increased risk of CV damage, metabolic and bone diseases. This review focuses on mechanisms underlying the mutual interplay between aldosterone and PTH as well as their potential impact on CV, metabolic and bone health. PTH stimulates aldosterone secretion by increasing the calcium concentration in the cells of the adrenal zona glomerulosa as a result of binding to the PTH/PTH-rP receptor and indirectly by potentiating angiotensin 2 induced effects. This may explain why after parathyroidectomy lower aldosterone levels are seen in parallel with improved cardiovascular outcomes. Aldosterone mediated effects are inappropriately pronounced in conditions such as chronic heart failure, excess dietary salt intake (relative aldosterone excess) and primary aldosteronism. PTH is increased as a result of (1) the MR (mineralocorticoid receptor) mediated calciuretic and magnesiuretic effects with a trend of hypocalcemia and hypomagnesemia; the resulting secondary hyperparathyroidism causes myocardial fibrosis and disturbed bone metabolism; and (2) direct effects of aldosterone on parathyroid cells via binding to the MR. This adverse sequence is interrupted by mineralocorticoid receptor blockade and adrenalectomy. Hyperaldosteronism due to klotho deficiency results in vascular calcification, which can be mitigated by spironolactone treatment. In view of the documented reciprocal interaction between aldosterone and PTH as well as the potentially ensuing target organ damage, studies are needed to evaluate diagnostic and therapeutic strategies to address this increasingly recognized pathophysiological phenomenon.

Kidney stones: a fetal origins hypothesis

Kidney stones are common, with a multifactorial etiology involving dietary, environmental, and genetic factors. In addition, patients with nephrolithiasis are at greater risk of hypertension, diabetes mellitus, metabolic syndrome, and osteoporosis, although the basis for this is not fully understood. All of these renal stone-associated conditions have also been linked with adverse early-life events, including low-birth weight, and it has been suggested that this developmental effect is due to excess exposure to maternal glucocorticoids in utero. This is proposed to result in long-term increased hypothalamic-pituitary-axis activation; there are mechanisms through which this effect could also promote urinary lithogenic potential. We therefore hypothesize that the association between renal stone disease and hypertension, diabetes mellitus, metabolic syndrome, and osteoporosis may be related by a common pathway of programming in early life, which, if validated, would implicate the developmental origins hypothesis in the etiology of nephrolithiasis.

Effect of eplerenone on parathyroid hormone levels in patients with primary hyperparathyroidism: a randomized, double-blind, placebo-controlled trial

BACKGROUND

Increasing evidence suggests the bidirectional interplay between parathyroid hormone and aldosterone as an important mechanism behind the increased risk of cardiovascular damage and bone disease observed in primary hyperparathyroidism. Our primary object is to assess the efficacy of the mineralocorticoid receptor-blocker eplerenone to reduce parathyroid hormone secretion in patients with parathyroid hormone excess.

METHODS/DESIGN

Overall, 110 adult male and female patients with primary hyperparathyroidism will be randomly assigned to eplerenone (25 mg once daily for 4 weeks and 4 weeks with 50 mg once daily after dose titration] or placebo, over eight weeks. Each participant will undergo detailed clinical assessment, including anthropometric evaluation, 24-h ambulatory arterial blood pressure monitoring, echocardiography, kidney function and detailed laboratory determination of biomarkers of bone metabolism and cardiovascular disease.The study comprises the following exploratory endpoints: mean change from baseline to week eight in (1) parathyroid hormone(1-84) as the primary endpoint and (2) 24-h systolic and diastolic ambulatory blood pressure levels, NT-pro-BNP, biomarkers of bone metabolism, 24-h urinary protein/albumin excretion and echocardiographic parameters reflecting systolic and diastolic function as well as cardiac dimensions, as secondary endpoints.

DISCUSSION

In view of the reciprocal interaction between aldosterone and parathyroid hormone and the potentially ensuing target organ damage, the EPATH trial is designed to determine whether eplerenone, compared to placebo, will effectively impact on parathyroid hormone secretion and improve cardiovascular, renal and bone health in patients with primary hyperparathyroidism.

TRIAL REGISTRATION

ISRCTN33941607.

Aldosterone and parathyroid hormone: a precarious couple for cardiovascular disease

Animal and human studies support a clinically relevant interaction between aldosterone and parathyroid hormone (PTH) levels and suggest an impact of the interaction on cardiovascular (CV) health. This review focuses on mechanisms behind the bidirectional interactions between aldosterone and PTH and their potential impact on the CV system. There is evidence that PTH increases the secretion of aldosterone from the adrenals directly as well as indirectly by activating the renin-angiotensin system. Upregulation of aldosterone synthesis might contribute to the higher risk of arterial hypertension and of CV damage in patients with primary hyperparathyroidism. Furthermore, parathyroidectomy is followed by decreased blood pressure levels and reduced CV morbidity as well as lower renin and aldosterone levels. In chronic heart failure, the aldosterone activity is inappropriately elevated, causing salt retention; it has been argued that the resulting calcium wasting causes secondary hyperparathyroidism. The ensuing intracellular calcium overload and oxidative stress, caused by PTH and amplified by the relative aldosterone excess, may increase the risk of CV events. In the setting of primary aldosteronism, renal and faecal calcium loss triggers increased PTH secretion which in turn aggravates aldosterone secretion and CV damage. This sequence explains why adrenalectomy and blockade of the mineralocorticoid receptor tend to decrease PTH levels in patients with primary aldosteronism. In view of the reciprocal interaction between aldosterone and PTH and the potentially ensuing CV damage, studies are urgently needed to evaluate diagnostic and therapeutic strategies addressing the interaction between the two hormones.

Congestive heart failure: where homeostasis begets dyshomeostasis

Despite today's standard of care, aimed at preventing homeostatic neurohormonal activation, one in every five patients recently hospitalized with congestive heart failure (CHF) will be readmitted within 30 days of discharge because of a recurrence of their symptoms and signs. In light of recent pathophysiological insights, it is now propitious to revisit CHF with a view toward complementary and evolving management strategies. CHF is a progressive systemic illness. Its features include: oxidative stress in diverse tissues; an immunostimulatory state with circulating proinflammatory cytokines; a wasting of soft tissues; and a resorption of bone. Its origins are rooted in homeostatic mechanisms gone awry to beget dyshomeostasis. For example, marked excretory losses of Ca2+ and Mg2+ accompany renin-angiotensin-aldosterone system activation, causing ionized hypocalcemia and hypomagnesemia that lead to secondary hyperparathyroidism with consequent bone resorption and a propensity to atraumatic fractures. Parathyroid hormone accounts for paradoxical intracellular Ca2+ overloading in diverse tissues and consequent systemic induction of oxidative stress. In cardiac myocytes and mitochondria, these events orchestrate opening of the mitochondrial permeability transition pore with an ensuing osmotic-based destruction of these organelles and resultant cardiomyocyte necrosis with myocardial scarring. Contemporaneous with Ca2+ and Mg2+ dyshomeostasis is hypozincemia and hyposelenemia, which compromise metalloenzyme-based antioxidant defenses, whereas hypovitaminosis D threatens Ca2+ stores needed to prevent secondary hyperparathyroidism. An intrinsically coupled dyshomeostasis of intracellular Ca2+ and Zn2+, representing pro-oxidant and antioxidant, respectively, is integral to regulating the mitochondrial redox state; it can be uncoupled by a Zn2+ supplement in favor of antioxidant defenses. Hence, the complementary use of nutriceuticals to nullify dyshomeostatic responses involving macro- and micronutrients should be considered. Evolving strategies with mitochondria-targeted interventions interfering with their uptake of Ca2+ or serving as selective antioxidant or mitochondrial permeability transition pore inhibitor may also prove efficacious in the overall management of CHF.

Temporal responses to intrinsically coupled calcium and zinc dyshomeostasis in cardiac myocytes and mitochondria during aldosteronism

Intracellular Ca(2+) overloading, coupled to induction of oxidative stress, is present at 4-wk aldosterone/salt treatment (ALDOST). This prooxidant reaction in cardiac myocytes and mitochondria accounts for necrotic cell death and subsequent myocardial scarring. It is intrinsically linked to increased intracellular zinc concentration ([Zn(2+)](i)) serving as an antioxidant. Herein, we addressed the temporal responses in coupled Ca(2+) and Zn(2+) dyshomeostasis, reflecting the prooxidant-antioxidant equilibrium, by examining preclinical (week 1) and pathological (week 4) stages of ALDOST to determine whether endogenous antioxidant defenses would be ultimately overwhelmed to account for this delay in cardiac remodeling. We compared responses in cardiomyocyte free [Ca(2+)](i) and [Zn(2+)](i) and mitochondrial total [Ca(2+)](m) and [Zn(2+)](m), together with biomarkers of oxidative stress and antioxidant defenses, during 1- and 4-wk ALDOST. At week 1 and compared with controls, we found: 1) elevations in [Ca(2+)](i) and [Ca(2+)](m) were coupled with [Zn(2+)](i) and [Zn(2+)](m); 2) increased mitochondrial H(2)O(2) production, cardiomyocyte xanthine oxidase activity, and cardiac and mitochondrial 8-isoprostane levels, counterbalanced by increased activity of antioxidant proteins, enzymes, and the nonenzymatic antioxidants that can be considered as cumulative antioxidant capacity; some of these enzymes and proteins (e.g., metallothionein-1, Cu/Zn-superoxide, glutathione synthase) are regulated by metal-responsive transcription factor-1; and 3) although these augmented antioxidant defenses were sustained at week 4, they fell short in combating the persistent intracellular Ca(2+) overloading and marked rise in cardiac tissue 8-isoprostane and mitochondrial transition pore opening. Thus a coupled Ca(2+) and Zn(2+) dyshomeostasis occurs early during ALDOST in cardiac myocytes and mitochondria that regulate redox equilibrium until week 4 when ongoing intracellular Ca(2+) overloading and prooxidants overwhelm antioxidant defenses.

Causes and consequences of zinc dyshomeostasis in rats with chronic aldosteronism

Iterations in Ca2+ and Mg2+ balance accompany aldosteronism (inappropriate for dietary Na+ intake). Increased Zn excretion and Zn translocation to injured tissues, including the heart, also occurs. Several causes and consequences of Zn dyshomeostasis in rats receiving aldosterone/salt treatment (ALDOST) were examined. (1) To study the role of urinary acidification in promoting hyperzincuria, acetazolamide (75 mg/kg), a carbonic anhydrase inhibitor, was used as cotreatment to raise urinary HCO3 excretion. (2) To assess Zn levels in the heart, including cardiomyocyte cytosolic free [Zn2+]i and mitochondrial Zn, the expression of metallothionein (MT-I), a Zn binding protein, and biomarkers of oxidative stress were examined. (3) Oxidative stress and cardiac pathology in response to ZnSO4 supplement (40 mg/d) were also studied. Comparison of controls and rats receiving 4 weeks ALDOST revealed the following: (1) an acidification of urine and metabolic alkalosis associated with increased urinary Zn excretion and hypozincemia, each of which were prevented by acetazolamide; (2) a rise in cardiac Zn, including increased [Zn2+]i and mitochondrial Zn, associated with increased tissue MT-I, 8-isoprostane, malondialdehyde, and gp91(phox), coupled with oxidative stress in plasma and urine; (3) ZnSO4 prevented hypozincemia, but not ionized hypocalcemia, and attenuated oxidative stress and microscopic scarring without preventing the vasculitis and perivascular fibrosis of intramural coronary arteries. Thus, the hyperzincuria seen with ALDOST is due to urinary acidification. The oxidative stress that appears in the heart is accompanied by increased tissue Zn serving as an antioxidant. Cotreatment with ZnSO4 attenuated cardiomyocyte necrosis; however, polynutrient supplement may be required to counteract the dyshomeostasis of all 3 cations that accompanies aldosteronism and contributes to cardiac pathology.

The association of nephrolithiasis with hypertension and obesity: a review

Kidney stones affect hypertensive patients disproportionately compared to normotensive individuals. On the other hand, some prospective data suggest that a history of nephrolithiasis was associated with a greater tendency to develop hypertension. Newer epidemiologic data also link obesity and diabetes, features of the metabolic syndrome, with nephrolithiasis. In this review, the association of hypertension, diabetes, and obesity with nephrolithiasis is reviewed, and possible pathogenic mechanisms are discussed. Patients with hypertension may have abnormalities of renal calcium metabolism, but data confirming this hypothesis are inconsistent. Higher body mass index and insulin resistance (i.e., the metabolic syndrome) may be etiologic in uric acid nephrolithiasis as increasing body weight is associated with decreasing urinary pH. The possibility that common pathophysiologic mechanisms underly these diseases is intriguing, and if better understood, could potentially lead to better therapies for stone prevention. Both hypertension and stones might be addressed through lifestyle modification to prevent weight gain. Adoption of a lower sodium diet with increased fruits and vegetables and low-fat dairy products, (for example, the dietary approaches to stop hypertension(DASH) diet), may be useful to prevent both stones and hypertension. In those patients in whom dietary modification and weight loss are ineffective, thiazide diuretics are likely to improve blood pressure control and decrease calciuria.

Preventing oxidative stress in rats with aldosteronism by calcitriol and dietary calcium and magnesium supplements

BACKGROUND

Prominent features of the clinical syndrome of congestive heart failure (CHF) include aldosteronism and the presence of oxidative stress. Secondary hyperparathyroidism (SHPT) accompanies aldosteronism due to increased urinary and fecal excretion of Ca. SHPT accounts for intracellular Ca overloading of diverse cells, including peripheral blood mononuclear cells (PBMC), and the appearance of oxidative stress. Parathyroidectomy or a Ca channel blocker each prevent these responses. Herein, we hypothesized calcitriol, or 1,25(OH)2D3, plus a diet supplemented with Ca and Mg (CMD) would prevent SHPT and Ca overloading of PBMC and thereby oxidative stress in these cells in rats receiving aldosterone/salt treatment (ALDOST).

METHODS AND RESULTS

In rats with ALDOST for 4 weeks, without or with CMD, we monitored plasma-ionized [Ca]o and parathyroid hormone (PTH), and PBMC cytosolic-free [Ca]i and H2O2 production. Untreated, age- and gender-matched rats served as controls. Compared to controls, ALDOST led to an expected fall in plasma [Ca]o level with accompanying rise in plasma PTH level and intracellular Ca overloading of PBMC and their increased production of H2O2. CMD prevented SHPT and abrogated intracellular Ca overloading of PBMC and their increased H2O2 production.

CONCLUSIONS

The appearance of SHPT in aldosteronism, induced by fallen plasma [Ca]o, leads to PTH-mediated Ca overloading of PBMC and their increased production of H2O2. SHPT in rats with aldosteronism can be prevented by calcitriol and a diet supplemented with Ca and Mg. These findings raise the prospect that the SHPT found in CHF could be managed with macro- and micronutrients.

Calcium paradox of aldosteronism and the role of the parathyroid glands

The hypercalciuria and hypermagnesuria that accompany aldosteronism contribute to a fall in plasma ionized extracellular Ca2+ and Mg2+ concentrations ([Ca2+]o and [Mg2+]o). Despite these losses and the decline in extracellular levels of these cations, total intracellular and cytosolic free Ca2+ concentration ([Ca2+]i) is increased and oxidative stress is induced. This involves diverse tissues, including peripheral blood mononuclear cells (PBMC) and plasma. The accompanying elevation in plasma parathyroid hormone (PTH) and reduction in bone mineral density caused by aldosterone (Aldo)-1% NaCl treatment (AldoST) led us to hypothesize that Ca2+ loading and altered redox state are due to secondary hyperparathyroidism (SHPT). Therefore, we studied the effects of total parathyroidectomy (PTx). In rats receiving AldoST, without or with a Ca2+-supplemented diet and/or PTx, we monitored urinary Ca2+ and Mg2+ excretion; plasma [Ca2+]o, [Mg2+]o, and PTH; PBMC [Ca2+]i and H2O2 production; plasma α1-antiproteinase activity; total Ca2+ and Mg2+ in bone, myocardium, and rectus femoris; and gp91phox labeling in the heart. We found that 1) the hypercalciuria and hypermagnesuria and decline ( P < 0.05) in plasma [Ca2+]o and [Mg2+]o that occur with AldoST were not altered by the Ca2+-supplemented diet alone or with PTx; 2) the rise ( P < 0.05) in plasma PTH with AldoST, with or without the Ca2+-supplemented diet, was prevented by PTx; 3) increased ( P < 0.05) PBMC [Ca2+]i and H2O2 production, increased total Ca2+ in heart and skeletal muscle, and fall in bone Ca2+ and Mg2+ and plasma α1-antiproteinase activity with AldoST were abrogated ( P < 0.05) by PTx; and 4) gp91phox activation in right and left ventricles at 4 wk of AldoST was attenuated by PTx. AldoST is accompanied by SHPT, with parathyroid gland-derived calcitropic hormones being responsible for Ca2+ overload in diverse tissues and induction of oxidative stress. SHPT plays a permissive role in the proinflammatory vascular phenotype.

Bone loss in rats with aldosteronism

OBJECTIVE

We hypothesized that aldosteronism is accompanied by hypercalciuria and hypermagnesuria that lead to bone loss, which could be rescued by hydrochlorothiazide and spironolactone.

METHODS

We monitored 24-hour urinary Ca and Mg excretion; plasma ionized [Ca]o and [Mg]o and plasma K; and bone mineral density of the femur. The following groups (n=5 in each group) were studied: age- and gender-matched, untreated controls; controls + 4 weeks hydrochlorothiazide; 4 weeks aldosterone/salt treatment (ALDOST, 0.75 mug/h and dietary 1% NaCl/0.4% KCl); 4 weeks ALDOST+hydrochlorothiazide (50 mg/kg in prepared food); and 4 weeks ALDOST+hydrochlorothiazide+spironolactone (200 mg/kg day in divided doses by twice-daily gavage).

RESULTS

ALDOST increased (P<0.05) urinary Ca and Mg excretion four- and twofold, respectively; hydrochlorothiazide co-treatment attenuated (P<0.05) Ca excretion in controls and during ALDOST without affecting augmented Mg excretion whereas hydrochlorothiazide+spironolactone normalized Ca and reduced Mg excretion (P<0.05). Compared with controls, plasma [Ca]o at 4 weeks of ALDOST was reduced (0.89+/-0.02 versus 0.83+/-0.03 mmol/L; P<0.05) but remained no different from levels in controls with hydrochlorothiazide and hydrochlorothiazide+spironolactone (0.88+/-0.04 and 0.97+/-0.03 mmol/L, respectively). Plasma [Mg]o fell (P<0.05) with ALDOST+hydrochlorothiazide (0.23+/-0.01 versus 0.34+/-0.01 mmol/L) and was prevented with spironolactone co-treatment (0.33+/-0.01 mmol/ dL). Hypokalemia (2.9+/-0.2 mmol/L) occurred in rats with ALDOST+hydrochlorothiazide but not with spironolactone co-treatment. At 4 weeks of ALDOST, plasma parathyroid hormone was increased (30+/-4 versus 11+/-3 pg/mL; P<0.05) and bone mineral density was reduced (0.153+/-0.006 versus 0.170+/-0.002 g/cm; P<0.05). Co-treatments with either hydrochlorothiazide or hydrochlorothiazide+spironolactone each prevented bone loss.

CONCLUSIONS

Hypercalciuria and hypermagnesuria accompany aldosteronism and account for a decline in their plasma ionized concentrations and secondary hyperparathyroidism with bone resorption. Attenuation of bone loss in aldosteronism can be achieved with hydrochlorothiazide; however, mono- and divalent cation homeostasis, together with bone integrity, are each preserved with the combination hydrochlorothiazide+spironolactone.

Diuretics and Bone Loss in Rats With Aldosteronism

OBJECTIVES

We hypothesized that the increased urinary Ca2+ and Mg2+ excretion and bone loss that accompanies aldosteronism is aggravated with furosemide and is attenuated by spironolactone.

BACKGROUND

Furosemide, a loop diuretic, is commonly used in patients with congestive heart failure (CHF), in which chronic, inappropriate (dietary Na+) elevations in plasma aldosterone (ALDO) and a catabolic state that includes bone wasting are expected.

METHODS

In age- and gender-matched, untreated controls, four weeks of aldosterone/salt treatment (ALDO/salt, 0.75 microg/h + 1% NaCl/0.4% KCl in drinking water), four weeks of ALDO/salt + furosemide (40 mg/kg in prepared food), and four weeks of ALDO/salt + furosemide + spironolactone (200 mg/kg/day in divided doses by twice-daily gavage), we monitored: 24-h urinary Ca2+ and Mg2+ excretion; plasma-ionized [Ca2+]o and [Mg2+]o, K+, and parathyroid hormone (PTH); and bone mineral density (BMD) in the femur.

RESULTS

The ALDO/salt increased (p < 0.05) urinary Ca2+ and Mg2+ excretion (4,969 +/- 1,078 and 3,856 +/- 440 microg/24 h, respectively) compared with controls (896 +/- 138 and 970 +/- 137 microg/24 h, respectively); furosemide co-treatment further increased (p < 0.05) urinary Ca2+ and Mg2+ excretion (6,976 +/- 648 and 6,199 +/- 759 microg/24 h, respectively), whereas spironolactone co-treatment attenuated (p < 0.05) these incremental losses (4,003 +/- 515 and 3,915 +/- 972 microg/24 h). Plasma [Ca2+]o was reduced (p < 0.05) at week 4 ALDO/salt + furosemide and was accompanied by hypokalemia (<3.4 mmol/l) that were rescued by spironolactone. Plasma PTH was increased (p < 0.05) compared with controls (30 +/- 4 vs. 11 +/- 3 pg/ml, respectively), whereas BMD was decreased (p < 0.05) with ALDO/salt and ALDO/salt + furosemide, but not with spironolactone co-treatment.

CONCLUSIONS

In aldosteronism, hypercalciuria and hypermagnesuria and accompanying decrease in plasma-ionized [Ca2+]o and [Mg2+]o lead to hyperparathyroidism that accounts for bone wasting. Furosemide exaggerates these losses, whereas its combination with spironolactone attenuates these responses to prevent bone loss.

Hyperparathyroidism and the Calcium Paradox of Aldosteronism

BACKGROUND

Aldosteronism may account for oxi/nitrosative stress, a proinflammatory phenotype, and wasting in congestive heart failure. We hypothesized that aldosterone/1% NaCl treatment (ALDOST) in rats enhances Ca2+ and Mg2+ excretion and leads to systemic effects, including bone loss.

METHODS AND RESULTS

At 1, 2, 4, and 6 weeks of ALDOST, we monitored Ca2+ and Mg2+ excretion, ionized [Ca2+]o and [Mg2+]o, parathyroid hormone and 1-antiproteinase activity in plasma, bone mineral density, bone strength, Ca2+ and Mg2+ content in peripheral blood mononuclear cells (PBMCs) and ventricular tissue, and lymphocyte H2O2 production. A separate group received spironolactone (Spiro), an aldosterone receptor antagonist. Age- and gender-matched unoperated and untreated rats served as controls. ALDOST induced a marked (P<0.05) and persistent rise in urinary and fecal Ca2+ and Mg2+ excretion, a progressive reduction (P<0.05) in [Ca2+]o and [Mg2+]o, and an elevation in parathyroid hormone (P<0.05) with a fall (P<0.05) in bone mineral density and strength. An early, sustained increase (P<0.05) in PBMC Ca2+ and Mg2+ was found, together with an increase (P<0.05) in tissue Ca2+. Plasma 1-antiproteinase activity was reduced (P<0.05), whereas lymphocyte H2O2 production was increased (P<0.05) at all time points. Spiro cotreatment attenuated (P<0.05) urinary and fecal Ca2+ and Mg2+ excretion, prevented the fall in [Ca2+]o and [Mg2+]o, rescued bone mineral density and strength, and prevented Ca2+ overloading of PBMCs and cardiomyocytes.

CONCLUSIONS

In aldosteronism, Ca2+ and Mg2+ losses lead to a fall in [Ca2+]o and [Mg2+]o with secondary hyperparathyroidism and bone resorption. Ca2+ overloading of PBMCs and cardiac tissue leads to oxi/nitrosative stress and a proinflammatory phenotype.

Loss of bone minerals and strength in rats with aldosteronism

Congestive heart failure (CHF) is a clinical syndrome with origins rooted in a salt-avid state largely mediated by effector hormones of the circulating renin-angiotensin-aldosterone system. Other participating neurohormones include catecholamines, endothelin-1, and arginine vasopressin. CHF is accompanied by a systemic illness of uncertain causality. Features include the appearance of oxidative/nitrosative stress and a wasting of tissues including bone. Herein we hypothesized that inappropriate (relative to dietary Na+) elevations in plasma aldosterone (Aldo) contribute to an altered redox state, augmented excretion of divalent cations, and in turn, a loss of bone minerals and strength. In uninephrectomized rats that received chronic Aldo and 1% NaCl treatment for 4-6 wk, we monitored plasma alpha1-antiproteinase activity, which is an inverse correlate of oxidative/nitrosative stress; plasma concentrations of ionized Mg2+ and Ca2+; urinary Mg2+ and Ca2+ excretion; and bone mineral composition and strength to flexure stress. Compared with controls, we found reductions in plasma alpha1-antiproteinase activity and ionized Mg2+ and Ca2+ together with persistently elevated urinary Mg2+ and Ca2+ excretion, a progressive loss of bone mineral density and content with reduced Mg2+ and Ca2+ concentrations, and a reduction in cortical bone strength. Thus the hypermagnesuria and hypercalciuria that accompany chronic Aldo-1% NaCl treatment contribute to the systemic appearance of oxidative/nitrosative stress and a wasting of bone minerals and strength.

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

Reduced concentration of serum ionized calcium and increased urinary calcium excretion have been reported in primary aldosteronism and glucocorticoid-treated patients. A reduced activity of the 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta HSD2) results in overstimulation of the mineralocorticoid receptor by cortisol. Whether inhibition of the 11 beta HSD2 by glycyrrhetinic acid (GA) may increase renal calcium excretion is unknown. Serum and urinary electrolyte and creatinine, serum ionized calcium, urinary calcium excretion, and the steroid metabolites (THF+5 alpha THF)/THE as a parameter of 11 beta HSD2 activity were repeatedly measured in 20 healthy subjects during baseline conditions and during 1 wk of 500 mg/d GA. One week of GA induced a maximal increment of 93% in (THF+5 alpha THF)/THE. Ambulatory BP was significantly higher at day 7 of GA than at baseline (126/77 +/- 10/7 versus 115/73 +/- 8/6 mmHg; P < 0.001 for systolic; P < 0.05 for diastolic). During GA administration, serum ionized calcium decreased from 1.26 +/- 0.05 to 1.18 +/- 0.04 mmol/L (P < 0.0001), and absolute urinary calcium excretion was enhanced from 29.2 +/- 3.6 to 31.9 +/- 3.1 micromol/L GFR (P < 0.01). Fractional calcium excretion increased from 2.4 +/- 0.3 to 2.7 +/- 0.3% (P < 0.01) and was negatively correlated to the fractional sodium excretion during GA (R = -0.35; P < 0.001). Moreover, serum potassium correlated positively with serum ionized calcium (R = 0.66; P < 0.0001). Inhibition of 11 beta HSD2 activity is sufficient to significantly increase the fractional excretion of calcium and decrease serum ionized calcium, suggesting decreased tubular reabsorption of this divalent cation under conditions of renal glucocorticoid/mineralocorticoid excess. The likely site of steroid-regulated renal calcium handling appears to be the distal tubule.

A prospective study of hypertension and the incidence of kidney stones in men

OBJECTIVE

To examine whether hypertension predicts the incidence of kidney stone disease.

DESIGN

Prospective cohort study (the Olivetti Prospective Heart Study).

SETTING

The Olivetti factory in Southern Italy.

SUBJECTS

Five hundred and three male workers, aged 21 - 68 years, with no evidence of kidney stone disease at baseline. Follow-up 8 years.

MAIN OUTCOME MEASURES

Anthropometry, blood pressure, biochemistry and history of kidney stone disease were evaluated at the baseline examination in 1987. Occurrence of kidney stone disease was evaluated again in 1994-1995. Hypertension was defined as systolic blood pressure > or = 160 or diastolic blood pressure, > or = 95 mmHg or both, or being on drug therapy for hypertension. Occurrence of kidney stone disease was defined as radiological or echographic evidence of calculi or documented passage of one or more stones.

RESULTS

At baseline, 114/503 men (22.7%) had hypertension and 32 were on drug treatment. After 8 years, 52 (10.3%) incident cases of kidney stone disease were detected. The majority (n = 45) had a documented passage of one or more stones. The incidence of kidney stone disease was higher in hypertensive than in normotensive men (19/114 (16.7%) versus 33/389 (8.5%); P = 0.011). Hypertensive men had a greater risk of developing kidney stones than normotensive ones (RR 1.96; 95% confidence interval 1.16-3.32). The risk was unaffected by the exclusion of treated hypertensives (2.01; 1.13-3.59) and after adjustment for age (1.89; 1.12-3.18), body weight (1.78; 1.05-3.00) or height (2.00; 1.19-3.38).

CONCLUSIONS

Hypertension in middle-aged men is a significant predictor of kidney stone disease rather than a consequence of renal damage caused by the kidney stones.

Drug- and nutrition-induced hypophosphatemia: mechanisms and relevance in the critically ill

OBJECTIVE

To provide an outline of the drugs and nutritional therapy that could contribute to the development of hypophosphatemia in the critically ill patient.

DATA SOURCES

Computerized abstracting services, references to primary literature articles, and review publications were screened for references to drug- or nutrition-related hypophosphatemia.

STUDY SELECTION

Studies primarily describing responses in adults were selected. Animal research is described that illustrates findings in humans.

DATA EXTRACTION

Information was abstracted from the findings of individual case reports and clinical trials.

DATA SYNTHESIS

Data are organized by mechanism of possible effect on serum phosphate concentration. No reference is made to drugs that do not have an effect on phosphate metabolism.

CONCLUSIONS

Hypophosphatemia can have significant effects that would hinder recovery of the critically ill patient. Antacids, catecholamines, beta-adrenergic agonists, sodium bicarbonate, and acetazolamide are commonly used therapeutic agents that could contribute significantly to the development of hypophosphatemia. Provision of nutrition to the chronically malnourished individual or chronic administration of phosphate-depleted parenteral nutrition could produce symptoms associated with hypophosphatemia. Other drugs could have a mild effect on lowering serum phosphate concentrations, but would be unlikely to produce symptoms unless combined with other etiologies of hypophosphatemia.

Blood pressure and endocrine responses to changes in dietary sodium intake in cardiac transplant recipients. Implications for the control of sodium balance

BACKGROUND

The role of cardiac extrinsic innervation in the regulation of sodium balance and blood pressure is controversial.

METHODS AND RESULTS

We performed a double-blind study of endocrine and blood pressure responses to 5 days of low- (LS, 10 mmol/d) and 5 days of high- (350 mmol/d) sodium intake in 12 cardiac transplant recipients, 12 matched healthy subjects, and 12 matched subjects with untreated essential hypertension. In transplant recipients on low sodium, supine blood pressure was 137/94 +/- 8/4 (mean +/- SEM) mm Hg and plasma atrial natriuretic peptide (ANP) was 59.3 +/- 6.3 pg/mL; on high sodium, blood pressure was 148/97 +/- 5/3 mmHg (P < .05 for systolic pressure versus LS), and ANP was 94.3 +/- 10.6 pg/mL (P < .01 versus LS), respectively. Plasma ANP for those on each diet was significantly higher in the cardiac transplant recipients than in healthy or hypertensive controls; relative changes in plasma ANP in changing from low- to high-sodium diet were similar in each group. Urinary sodium excretion by the fifth day of each diet was similar in each group. Suppression of plasma renin activity and aldosterone by high-sodium diet was blunted in cardiac transplant recipients compared with healthy subjects (respectively, plasma renin activity: 1.41 +/- 0.30 versus 0.68 +/- 0.21 ng.mL-1 x h-1, P < .05; aldosterone: 391 +/- 35 versus 166 +/- 21 pmol/L, P < .05).

CONCLUSIONS

These results suggest that extensive denervation of the heart does not result in major abnormalities in regulation of large changes in sodium intake and that intact cardiac innervation is not required for plasma ANP responses to altered sodium intake. Blood pressure after cardiac transplantation is sensitive to reduced sodium intake.

Effects of calcium supplementation and deoxycorticosterone on plasma atrial natriuretic peptide and electrolyte excretion in spontaneously hypertensive rats

The effects of calcium and the mineralocorticoid deoxycorticosterone (DOC) on blood pressure were studied in four groups of spontaneously hypertensive rats (SHR): (1) control; (2) calcium; (3) deoxycorticosterone and; (4) deoxycorticosterone + calcium. Calcium was given as 1.5% calcium chloride in drinking fluid and deoxycorticosterone by weekly subcutaneous injections (25 mg kg-1). During the nine weeks of treatment the increase in systolic blood pressure was enhanced in the deoxycorticosterone and attenuated in the calcium group, whereas the deoxycorticosterone + calcium group did not deviate from control. Total plasma calcium was elevated in the calcium group. Plasma concentrations of sodium and atrial natriuretic peptide (ANP) were increased by deoxycorticosterone while neither of the calcium-treated groups differed from control in these respects. Urinary excretions of calcium and sodium were increased in both groups receiving calcium, and also the deoxycorticosterone group excreted more calcium into urine than the control. Adrenergic nerve density in a section of the mesenteric artery and the urinary excretion of noradrenaline and adrenaline were similar in all study groups. The results indicate that calcium supplementation can attenuate the development of hypertension and prevent the deoxycorticosterone-induced blood pressure rise in SHR, possibly by influencing sodium metabolism as seen in increased natriuresis, and by preventing the actions of deoxycorticosterone on sodium balance.