The calcium paradox of essential hypertension

Relationship between vitamin D deficiency and cardiovascular disease

Epidemiological studies have found that low 25-hydroxyvitamin D levels may be associated with coronary risk factors and adverse cardiovascular outcomes. Additionally, vitamin D deficiency causes an increase in parathyroid hormone, which increases insulin resistance and is associated with diabetes, hypertension, inflammation, and increased cardiovascular risk. In this review, we analyze the association between vitamin D supplementation and the reduction in cardiovascular disease. The role of vitamin D deficiency in cardiovascular morbidity and mortality is still controversial, and larger scale, randomized placebo controlled trials are needed to investigate whether oral vitamin D supplementation can reduce cardiovascular risk. Given the low cost, safety, and demonstrated benefit of higher 25-hydroxyvitamin D levels, vitamin D supplementation should become a public health priority for combating common and costly chronic cardiovascular diseases.

The association between BsmI polymorphism and risk factors for atherosclerosis in patients with epilepsy taking valproate

PURPOSE

To evaluate the association between the BsmI polymorphism and vascular risk factors or metabolic syndrome in patients with epilepsy treated with valproate.

METHODS

We performed a cross-sectional study to determine glucose homeostasis, lipid profile, and evidence of metabolic syndrome, as well as the BsmI polymorphism in seizure free adults with epilepsy.

RESULTS

We recruited 75 patients with epilepsy to the current study. The frequency of the BsmI polymorphism was 22.7%. We found that patients with BsmI polymorphism had significantly higher total levels of triglycerides, total cholesterol, HDL-C and LDL-C. There were no differences in terms of fasting blood glucose level and fasting insulin levels between patients with the BsmI polymorphism and those with the wild type vitamin D receptor (VDR) gene. Insulin resistance was identified in 6 of 17 patients with the BsmI polymorphism, and 18 of 58 patients with the wild type VDR gene. We calculated the homeostasis model assessment (HOMA) index and found no difference in HOMA levels between the groups. Systolic blood pressure was higher in patients with the BsmI polymorphism. There was a higher prevalence of metabolic syndrome in patients with the BsmI polymorphism than in patients with the wild type gene. The prevalence of metabolic syndrome in BsmI polymorphism carriers was 64.7% compared with 41.4% in patients with the wild type VDR gene.

CONCLUSION

Young patients with epilepsy taking valproate who carry the BsmI polymorphism are at an increased risk of having vascular risk factors.

Disturbances in calcium metabolism and cardiomyocyte necrosis: the role of calcitropic hormones

A synchronized dyshomeostasis of extra- and intracellular Ca(2+), expressed as plasma ionized hypocalcemia and excessive intracellular Ca(2+) accumulation, respectively, represents a common pathophysiologic scenario that accompanies several diverse disorders. These include low-renin and salt-sensitive hypertension, primary aldosteronism and hyperparathyroidism, congestive heart failure, acute and chronic hyperadrenergic stressor states, high dietary Na(+), and low dietary Ca(2+) with hypovitaminosis D. Homeostatic responses are invoked to restore normal extracellular [Ca(2+)](o), including increased plasma levels of parathyroid hormone and 1,25(OH)(2)D(3). However, in cardiomyocytes these calcitropic hormones concurrently promote cytosolic free [Ca(2+)](i) and mitochondrial [Ca(2+)](m) overloading. The latter sets into motion organellar-based oxidative stress, in which the rate of reactive oxygen species generation overwhelms their detoxification by endogenous antioxidant defenses, including those related to intrinsically coupled increments in intracellular Zn(2+). In turn, the opening potential of the mitochondrial permeability transition pore increases, allowing for osmotic swelling and ensuing organellar degeneration. Collectively, these pathophysiologic events represent the major components to a mitochondriocentric signal-transducer-effector pathway to cardiomyocyte necrosis. From necrotic cells, there follows a spillage of intracellular contents, including troponins, and a subsequent wound healing response with reparative fibrosis or scarring. Taken together, the loss of terminally differentiated cardiomyocytes from this postmitotic organ and the ensuing replacement fibrosis each contribute to the adverse structural remodeling of myocardium and progressive nature of heart failure. In conclusion, hormone-induced ionized hypocalcemia and intracellular Ca(2+) overloading comprise a pathophysiologic cascade common to diverse disorders and that initiates a mitochondriocentric pathway to nonischemic cardiomyocyte necrosis.

Fibrosis in hypertensive heart disease: molecular pathways and cardioprotective strategies

Fibrosis is a fundamental component of the adverse structural remodelling of myocardium found in hypertensive heart disease (HHD). A replacement fibrosis appears at sites of previous cardiomyocyte necrosis to preserve the structural integrity of the myocardium. Such scarring has adverse functional consequences. The extensive distribution of fibrosis involving the right and left heart suggests cardiomyocyte necrosis is widespread. Together, the loss of these contractile elements and fibrous tissue deposition in the form of stiff in-series and in-parallel elastic elements contribute to the progressive failure of this normally efficient muscular pump. Pathogenic mechanisms modulating fibrous tissue formation at sites of repair include auto/paracrine properties of locally generated angiotensin II and endothelin-1. This study focuses on the signal-transducer-effector pathway involved in cardiomyocyte necrosis and the crucial pathogenic role of intracellular calcium overloading, and the subsequent induction of oxidative stress originating within its mitochondria that dictates the opening of the mitochondrial permeability transition pore. The ensuing osmotic destruction of these organelles is followed by necrotic cell death. It is now further recognized that calcium overloading of cardiac myocytes and mitochondria functioning as pro-oxidant is pathophysiologically counterbalanced by an intrinsically coupled zinc entry, which serves as an antioxidant. The prospect of raising intracellular zinc by adjuvant nutriceutical supplementation can, therefore, be preferentially exploited to uncouple this intrinsically coupled calcium-zinc dyshomeostasis in favour of endogenous antioxidant defences. Novel cardioprotective strategies may thus be at hand and deserve to be explored further in the overall management of patients with HHD.

Myocardial remodeling in low-renin hypertension: molecular pathways to cellular injury in relative aldosteronism

The pathologic hypertrophy of hypertensive heart disease is related to the quality, not the quantity, of myocardium; the presence of fibrosis is inevitably linked to structural and functional insufficiencies with increased cardiovascular risk. Elevations in plasma aldosterone that are inappropriate relative to dietary sodium, or relative aldosteronism, are accompanied by suppressed plasma renin activity, elevation in arterial pressure, and dyshomeostasis of divalent cations. The accompanying hypocalcemia, hypomagnesemia, and hypozincemia of aldosteronism contribute to the appearance of secondary hyperparathyroidism. Parathyroid hormone-mediated intracellular calcium overloading of cardiac myocytes and mitochondria leads to the induction of oxidative stress and molecular pathways associated with cardiomyocyte necrosis and scarring of myocardium, whereas the dyshomeostasis of zinc compromises antioxidant defenses. This dys-homeostasis of calcium and zinc, intrinsically coupling prooxidant calcium and antioxidant zinc, raises the prospect for therapeutic strategies designed to mitigate intracellular calcium overloading while enhancing zinc-mediated antioxidant defenses, thus preventing adverse myocardial remodeling with fibrosis, associated diastolic dysfunction, and cardiac arrhythmias.

[Modifications in intact parathyroid hormone, total serum calcium, and ionized calcium levels in the surgery of primary hyperparathyroidism for single adenoma]

INTRODUCTION

We evaluated total serum calcium (TSC) and ionized calcium (IC) and their correlation with intraoperative intact parathyroid hormone (iPTH) in the surgery of primary hyperparathyroidism in patients with a single adenoma.

MATERIAL AND METHOD

We performed a prospective, blind trial with determination of iPHT, TSC and IC in a cohort of surgical patients (n = 279; 244 were valid for the study) who underwent surgery in the Department of Surgery, Hospital de Cruces, between October 1999 and April 2006. Total calcium, ionic calcium and iPTH were measured in the outpatient department, on admission and intraoperatively (at anesthesia induction and every 5 minutes after surgical excision).

RESULTS

Levels of calcium and iPTH were corrected in 234 (95.9%) patients. iPTH decreased from abnormal preoperative values of 294.43 +/- 286.38 pg/ml to 97.89 +/- 121.01 mg/dl (minute 5), 58.58 +/- 58.37 pg/ml (minute 10), 44.62 +/- 54.77 pg/ml (minute 15), and 38.42 +/- 51.72 pg/ml (minute 20). TSC decreased from preoperative values of 10.93 +/- 1.04 mg/dl to 10.2 +/- 0.97 mg/dl (minute 5), 10.17 +/- 1.00 mg/dl (minute 10), 10.12 +/- 0.98 mg/ml (minute 15), and 10.09 +/- 1.03 mg/ml (minute 20). The results for ionized calcium were as follows: 4.90 +/- 0.63 mg/dl at induction, 4.84 +/- 0.61 mg/dl (minute 5), 4.84 +/- 0.66 mg/dl (minute 10), 4.82 +/- 0.63 mg/dl (minute 15), and 4.82 +/- 0.63 mg/dl (minute 20). Frozen samples were conclusive for parathyroid tissue (19.56 +/- 15.3 after excision).

CONCLUSIONS

Intraoperative total calcium levels may help to predict adequate elimination of parathyroid tissue in primary hyperparathyroidism when intraoperative iPTH is not available. Ionized calcium levels did not show the same decrease.

Vitamins for the elderly: from A to zinc

Nutritional status can be affected by a number of factors associated with increased age. Changes in appetite, taste, and swallowing can impact the eating habits of the elderly individual. In addition, the lower energy requirement of the elderly patient necessitates that these nutrients be consumed in greater density. Because many older adults have chronic diseases that may be affected by diet, providing optimal nutrition is especially important, and adequate stores of essential vitamins and minerals may play a key role in disease prevention and in modulating disease progression.

Vitamin D and disease prevention with special reference to cardiovascular disease

Circulating 25-hydroxyvitamin D [25(OH)D] is the hallmark for determining vitamin D status. Serum parathyroid hormone [PTH] increases progressively when 25(OH)D falls below 75 nmol/l. Concentrations of 25(OH)D below 50 nmol/l or even below 25 nmol/l are frequently observed in various population groups throughout the world. This paper highlights the relationship of vitamin D insufficiency with cardiovascular disease and non-insulin dependent diabetes mellitus, two diseases that account for up to 50% of all deaths in western countries. There is evidence from patients with end-stage renal disease that high PTH concentrations are causally related to cardiovascular morbidity and mortality. Activated vitamin D is able to increase survival in this patient group significantly. Moreover, already slightly enhanced PTH concentrations are associated with ventricular hypertrophy and coronary heart disease in the general population. Experimental studies have demonstrated that a lack of vitamin D action leads to hypertension in mice. Some intervention trials have also shown that vitamin D can reduce blood pressure in hypertensive patients. In young and elderly adults, serum 25(OH)D is inversely correlated with blood glucose concentrations and insulin resistance. Sun-deprived lifestyle, resulting in low cutaneous vitamin D synthesis, is the major factor for an insufficient vitamin D status. Unfortunately, vitamin D content of most foods is negligible. Moreover, fortified foods and over-the-counter supplements usually contain inadequate amounts of vitamin D to increase serum 25(OH)D to 75 nmol/l. As a consequence, legislation has to be changed to allow higher amounts of vitamin D in fortified foods and supplements.

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.

Vitamin D and the elderly

This review summarizes current knowledge on vitamin D status in the elderly with special attention to definition and prevalence of vitamin D insufficiency and deficiency, relationships between vitamin D status and various diseases common in the elderly, and the effects of intervention with vitamin D or vitamin D and calcium. Individual vitamin D status is usually estimated by measuring plasma 25-hydroxyvitamin D (25OHD) levels. However, reference values from normal populations are not applicable for the definition of vitamin D insufficiency or deficiency. Instead vitamin D insufficiency is defined as the lowest threshold value for plasma 25OHD (around 50 nmol/l) that prevents secondary hyperparathyroidism, increased bone turnover, bone mineral loss, or seasonal variations in plasma PTH. Vitamin D deficiency is defined as values below 25 nmol/l. Using these definitions vitamin D deficiency is common among community-dwelling elderly in the developed countries at higher latitudes and very common among institutionalized elderly, geriatric patients and patients with hip fractures. Vitamin D deficiency is an established risk factor for osteoporosis, falls and fractures. Clinical trials have demonstrated that 800 IU (20 microg) per day of vitamin D in combination with 1200 mg calcium effectively reduces the risk of falls and fractures in institutionalized patients. Furthermore, 400 IU (10 microg) per day in combination with 1000 mg calcium or 100 000 IU orally every fourth month without calcium reduces fracture risk in individuals over 65 years of age living at home. Yearly injections of vitamin D seem to have no effect on fracture risk probably because of reduced bioavailability. Simulation studies suggest that fortification of food cannot provide sufficient vitamin D to the elderly without exceeding present conventional safety levels for children. A combination of fortification and individual supplementation is proposed. It is argued that all official programmes should be evaluated scientifically. Epidemiological studies suggest that vitamin D insufficiency is related to a number of other disorders frequently observed among the elderly, such as breast, prostate and colon cancers, type 2 diabetes, and cardiovascular disorders including hypertension. However, apart from hypertension, causality has not been established through randomized intervention studies. It seems that 800 IU (20 microg) vitamin D per day in combination with calcium reduces systolic blood pressure in elderly women.

Intraoperative monitoring of kinetic total serum calcium levels in primary hyperparathyroidism surgery

BACKGROUND

In the setting of minimal approach Sestamibi-guided parathyroid surgery for primary hyperparathyroidism we evaluated if total serum calcium level monitoring is as valuable as intraoperative parathyroid hormone (iPTH) monitoring.

STUDY DESIGN

Prospective open single-blinded efficacy trial of two intraoperative diagnostic monitoring methods (iPTH and total serum calcium level) on a cohort of surgical patients. All patients (n = 35) were undergoing parathyroid surgery at the Department of General Surgery at B Cruces' Hospital, Vizcaya, Spain, between October 1999 and March 2001. Kinetics of serum levels of Ca and iPTH during surgery and time of prediction of cure for each method (measured in the clinic, admission, and intraoperatively, such as induction of anesthesia, and every 5 minutes after removal of adenoma) were analyzed.

RESULTS

Hypercalcemia and iPTH levels became corrected in 34 patients. Average serum calcium levels dropped from pathologic 11.07 +/- 0.41 mg/dL (mean +/- standard deviation) to normal values 9.7 +/- 0.82 mg/dL during the first intraoperative determination (minute 5), but mean iPTH decreased from pathologic (192 +/- 98 pg/mL) to normal values (39.93 +/- 25.12 pg/mL) during the third intraoperative determination (minute 15). Serum calcium level at 5 minutes after removal decreased by 100% in 34 patients, but iPTH only showed a similar drop during the third determination at 15 minutes. Frozen sections were conclusive for parathyroid tissue (20.56 +/- 10.3 minutes after removal).

CONCLUSIONS

Intraoperative measurement of total calcium level might be an easier and less expensive method than iPTH measurement in the prediction of cure during surgery for primary hyperparathyroidism resulting from adenoma.

Vitamin D in preventive medicine: are we ignoring the evidence?

Vitamin D is metabolised by a hepatic 25-hydroxylase into 25-hydroxyvitamin D (25(OH)D) and by a renal 1alpha-hydroxylase into the vitamin D hormone calcitriol. Calcitriol receptors are present in more than thirty different tissues. Apart from the kidney, several tissues also possess the enzyme 1alpha-hydroxylase, which is able to use circulating 25(OH)D as a substrate. Serum levels of 25(OH)D are the best indicator to assess vitamin D deficiency, insufficiency, hypovitaminosis, adequacy, and toxicity. European children and young adults often have circulating 25(OH)D levels in the insufficiency range during wintertime. Elderly subjects have mean 25(OH)D levels in the insufficiency range throughout the year. In institutionalized subjects 25(OH)D levels are often in the deficiency range. There is now general agreement that a low vitamin D status is involved in the pathogenesis of osteoporosis. Moreover, vitamin D insufficiency can lead to a disturbed muscle function. Epidemiological data also indicate a low vitamin D status in tuberculosis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel diseases, hypertension, and specific types of cancer. Some intervention trials have demonstrated that supplementation with vitamin D or its metabolites is able: (i) to reduce blood pressure in hypertensive patients; (ii) to improve blood glucose levels in diabetics; (iii) to improve symptoms of rheumatoid arthritis and multiple sclerosis. The oral dose necessary to achieve adequate serum 25(OH)D levels is probably much higher than the current recommendations of 5-15 microg/d.

Low vitamin D status: a contributing factor in the pathogenesis of congestive heart failure?

OBJECTIVES

This study was designed to evaluate the association between vitamin D status and congestive heart failure (CHF).

BACKGROUND

Impaired intracellular calcium metabolism is an important factor in the pathogenesis of CHF. The etiology of CHF, however, is not well understood.

METHODS

Twenty patients age <50 years and 34 patients age >/=50 years with New York Heart Association classes >/=2 and 34 control subjects age >/=50 years were recruited. N-terminal pro-atrial natriuretic peptide (NT-proANP), a predictor of CHF severity; vitamin D metabolites; and parameters of calcium metabolism were measured in fasting blood samples collected between November 2000 and March 2001.

RESULTS

Both groups of CHF patients had markedly increased serum levels of NT-proANP (p < 0.001), increased serum phosphorus levels (p < 0.001), and reduced circulating levels of both 25-hydroxyvitamin D (p < 0.001) and calcitriol (p < 0.001). Albumin-corrected calcium levels were reduced and parathyroid hormone levels were increased in the younger CHF patients compared with the controls (both p values <0.001). Moreover, parathyroid hormone levels tended to be higher in the elderly CHF patients than in the controls (p = 0.074). In a nonlinear regression analysis 25-hydroxyvitamin D and calcitriol were inversely correlated with NT-proANP (r(2) = 0.16; p < 0.001 and r(2) = 0.12; p < 0.01, respectively). The vitamin D genotype at the BmsI restriction site did not differ between the study groups.

CONCLUSIONS

The low vitamin D status can explain alterations in mineral metabolism as well as myocardial dysfunction in the CHF patients, and it may therefore be a contributing factor in the pathogenesis of CHF.

[Changes in calcium levels in blood and urine during various regimens of table salt intake in patients with essential arterial hypertension]

INTRODUCTION

It has been reported that changes in salt loading influence parameters of calcium metabolism in hypertensive subjects. It was also reported that response of blood pressure to salt intake is related to salt-induced increase in intracellular calcium and decrease in intracellular magnesium concentrations [1]. Several authors showed that salt-sensitive hypertensive subjects significantly decreased blood pressure after calcium intake which was emphasized by high salt intake. Resnick et al. showed that during high salt intake regimen increase in blood pressure was followed with decrease in serum calcium level, this was explained by the fact that high salt intake stimulates the calcium uptake by cells [2]. They also reported the following characteristics of hypertensive patients with additionally lower blood pressure as a response to calcium intake: salt-sensitive, low serum ionized calcium and plasma renin activity (PRA) values and high parathyroid hormonE (PTH) values and 1.25-(OH)2-D values. The aim of the study was to evaluate values of corrected and ionized serum and urine calcium in a group of salt-sensitive patients, salt-resistant patients and a whole group during normal salt-intake regimen, and a group without salt and during sodium load (10 g salt extra).

MATERIAL AND METHODS

In our study, 50 untreated patients (27 women and 23 men; average age 42 +/- 9.2 yrs; average BMI 27.91 +/- 4.6 kg/m2) with essential hypertension were put on a high salt regimen (200 mmol NaCl per day) for one week after a week on a low salt diet (20 mmol NaCl per day). On the last day of the normal regimen and during the 1st, 3rd and 5th day of low salt and high salt regimens, the following follow-up was carried out: total (corrected) serum calcium level and total urine calcium level, ionized serum calcium urine creatininE level; serum albumin and daily diuresis and blood pressure. All patients had normal sodium and potassium serum concentrations. Salt intake was checked by taking a specimen of 24-hour urine considered as satisfactory if sodium excretion of 100 to 150 mmol/d (mmol per day) was noted. During the whole hospital examination, calcium intake through hospital meals was standardized to about 817 mg of calcium daily. Salt sensitivity was defined as 10 mmHg increase in mean blood pressure at the end of high vs. low salt diet. Salt sensitive group consisted of 26 patients and salt insensitive of 24 patients.

RESULTS

According to sex, there was no statistically significant difference: 27 females (54%) and 24 males (46%). Average age of patients was 49 +/- 9.2 yrs, ranging from 21 to 64 with normal frequency distribution. Average body weight was 80.49 kg +/- 12.45 kg. Body height was from 150 to 192 cm with average of 170.12 +/- 10.53 cm. Average value of Body Mass Index (BMI in kg per square meter) was 27.91 +/- 4.6. In the studied patients average duration of hypertension was 6.98 +/- 6.4 yrs with non-homogeneous distribution. In 32 patients (64%) the medical history confirmed that one or more family members had hypertension. It was found that salt loading significantly decreased ionized calcium (F = 2.49; p < 0.05) and significantly increased urinary excretion of calcium (F = 5.22; p < 0.001) in salt sensitive patients in comparison with salt insensitive subjects. Serum calcium did not differ significantly during different salt intake regimens between two groups. Our study revealed no positive correlation between gender, age, BMI and family history and calcium metabolism.

CONCLUSION

The findings of this study support the opinion of altered calcium metabolism in hypertensive subjects sensitive to salt intake. By demonstrated results we tried to define clinically different pathophysiologic and potentially different therapeutic subgroups in hypertensive population and to point to clinical and biochemical heterogeneity of primary hypertension.

Endothelial vasodilatory function and blood pressure response to local and systemic hypercalcemia

BACKGROUND

Endothelial vasodilatory dysfunction occurs in primary hyperparathyroidism. Mechanistically it could be a sign of atherosclerosis, but improvement after parathyroidectomy suggests coupling to hypercalcemia and increased parathyroid hormone levels of patients.

METHOD

A total of 12 volunteers underwent forearm venous occlusion plethysmography with systemic (intravenous) and local (brachial artery) infusion of calcium. Endothelium-dependent and endothelium-independent vasodilations were evaluated at stable hypercalcemia through infusion of methacholine and nitroprusside into the brachial artery, and an endothelial function index was calculated as the ratio between them.

RESULTS

Normal ionized blood calcium values rose 0.24 +/- 0.09 mmol/L in the cubital venous blood during local calcium infusion and 0.32 +/- 0.16 mmol/L during the systemic infusion. The systemic infusion raised systolic blood pressure (114 +/- 13 to 121 +/- 10 mm Hg; P < .05). It decreased the function index (1.28 +/- 0.40 to 1.00 +/- 0.14; P < .05; n = 11) due to an elevated endothelium-independent vasodilation (EIDV) (P < .05), despite the fact that serum parathyroid hormone values decreased (P< .01). A similar trend in vasodilatory responses was seen during local calcium infusion when the function index correlated inversely to the local blood calcium (r = -0.58, P < .05; n = 12).

CONCLUSIONS

Acute hypercalcemia results in dose-related impairment in endothelial vasodilatory function and increased systolic blood pressure. This substantiates the importance of hypercalcemia for cardiovascular complications and prospects for normalization by active treatment in primary hyperparathyroidism.

Endothelial vasodilatory dysfunction in primary hyperparathyroidism is reversed after parathyroidectomy

BACKGROUND

Primary hyperparathyroidism (HPT) is accompanied by hypertension and a cardiovascular mortality. Impaired endothelium-dependent vasodilatation (EDV) occurs in hypertension but has not been fully investigated in HPT despite the vasoactive influences of parathyroid hormone.

METHODS

Twenty-five HPT patients and 25 normocalcemic control subjects, matched for age and gender, underwent forearm venous occlusion plethysmography. EDV and endothelium-independent vasodilatation (EIDV) were evaluated during local infusion of metacholine (2 and 4 micrograms/min) and nitroprusside (5 and 10 micrograms/min), respectively. The endothelial function index was calculated as the ratio of forearm blood flows during the high doses of metacholine and nitroprusside. Ambulatory 24-hour blood pressures and thickness of the intima-media complex of the carotid arteries were also measured; the latter is considered an early marker of atherosclerosis.

RESULTS

Endothelial function index was lower in the HPT patients compared with control subjects (1.01 +/- 0.26 vs 1.27 +/- 0.31, P = .003). Reinvestigation 10 months after parathyroidectomy showed normalization of the index (1.31 +/- 0.39, P = .01) due to a numeric increase in EDV and decrease in EIDV. The carotid intima-media thickness and blood pressure were similar in the groups and unaltered postoperatively.

CONCLUSIONS

Endothelial vasodilatory dysfunction is another indicator of the vascular disturbance of HPT and can be normalized by parathyroidectomy.

The effects of potassium, magnesium, calcium, and fiber on risk of stroke

Stroke mortality represents the third leading cause of death worldwide, after coronary artery disease and cancer. High blood pressure is a major risk factor for stroke. A recent study has identified potassium, magnesium, and fiber as significant modulators of stroke risk in men. The protective effects were particularly pronounced in hypertensive subjects. The observed protection may be due to direct and indirect effects of these nutrients on blood pressure and regulatory functions, such as endothelial function. A high intake of these nutrients, singularly or in combination, is associated with a more healthful overall lifestyle. The best strategy to achieve a high intake of these nutrients is a diet rich in fruits and vegetables.

Regulation of blood pressure with calcium-dependent dopamine synthesizing system in the brain and its related phenomena

The effects of calcium on blood pressure regulation remain controversial. Although the mechanism by which calcium increases blood pressure when it is given intravenously and acutely has been elucidated, that by which calcium reduces blood pressure when it is supplemented chronically and slightly through daily diet is unclear. From a number of animal experiments concerning the effects of calcium on blood pressure, we believe that calcium ions have two separate roles in the regulation of blood pressure through both central and peripheral systems: (1) calcium ions reduce blood pressure through a central, calcium/calmodulin-dependent dopamine-synthesizing system and (2) calcium ions increase blood pressure through an intracellular, calcium-dependent mechanism in the peripheral vasculature. These concepts were applied to elucidate the mechanisms underlying hypertension in spontaneously hypertensive rats (SHR) and changes in blood pressure in other experimental animals, and the following conclusions were reached. The decrease of the serum calcium level in spontaneously hypertensive rats (SHR) causes a decrease in calcium/calmodulin-dependent dopamine synthesis in the brain. The subsequent low level of brain dopamine induces hypertension. The increase in susceptibility to epileptic convulsions and the occurrence of hypertension in epileptic mice (El mice) may be linked through a lowering of calcium-dependent dopamine synthesis in the brain, and epilepsy and hypertension may be associated. Exercise leads to increases in calcium-dependent dopamine synthesis in the brain, and the increased dopamine levels induce physiological changes, including a decrease in blood pressure. Cadmium which is not distinguished from calcium by calmodulin, activates calmodulin-dependent functions in the brain, and increased dopamine levels may decrease blood pressure. In this report, our studies are considered in light of reports from many other laboratories.

Long-term effects of parathyroidectomy for primary hyperparathyroidism on arterial hypertension

The prevalence of arterial hypertension in primary hyperparathyroidism (PHPT) is higher than in the general population. With the aim of determining the evolution of hypertension associated with PHPT, we analyzed a group of 56 patients followed for a mean of 60 months (range 10-101 months) after successful parathyroidectomy for PHPT. The study group consisted of 16 men and 40 women. The mean age was 49 +/- 12 years (range 18-73 years). None of the patients had renal impairment. Two hypertensive patients died during the follow-up from complications related to their hypertension. Twelve (21.8%) patients were hypertensive before parathyroid surgery (systolic greater than 160 mmHg and/or diastolic greater than 90 mmHg). Pre-operative midregion serum parathyroid hormone concentration was higher in the hypertensive patients than in normotensive patients (2.7 +/- 2.4 vs 0.82 +/- 0.4 mu iEq/l, p = 0.018). Pre-operative creatinine clearance was lower in the hypertensive patients than in normotensive patients (65.4 +/- 27.5 vs 86.7 +/- 26 ml/min, p = 0.002). There were no significant differences between normotensive and hypertensive patients in age, sex, body weight, clinical manifestations, weight of parathyroid tissue removed, and calcium metabolism, or in plasma concentrations of magnesium, uric acid, cholesterol, proteins, or albumin. During follow-up, none of the patients with pre-operative hypertension became normotensive, whereas 32% of the patients who were normotensive preoperatively developed clinical hypertension. The global prevalence of postoperative hypertension was thus 48%. The patients that developed hypertension after parathyroidectomy were followed for a longer period than the normotensive patients (76 +/- 17 vs 53 +/- 10 months, p = 0.005), had a lower postoperative creatinine clearance (74 +/- 28 vs 90 +/- 25 mg/min, p = 0.07), and higher cholesterol levels (6.2 +/- 1.5 vs 5.5 +/- 0.9 mmol/L, p = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Minerals and blood pressure

The mineral elements sodium, potassium, calcium and magnesium play a central role in the normal regulation of blood pressure. In particular, these mineral elements have important interrelationships in the control of arterial resistance. These elements, especially sodium and potassium, also regulate the fluid balance of the body and, hence, influence the cardiac output. Evidence shows that the present levels of intake of mineral elements are not optimum for maintaining normal blood pressure but predispose to the development of arterial hypertension. Research results suggest that without sodium chloride (common salt) and other sodium compounds being added to the diet arterial hypertension would be virtually non existent. Moreover, blood pressure would not rise with age. In communities with a high consumption of added sodium, a high intake of potassium and, possibly, magnesium seem to protect against the development of arterial hypertension and the rise of blood pressure with age. A marked reduction of sodium intake is effective in treating even severe hypertension. A moderate restriction of sodium intake or an increase in potassium intake exert remarkable antihypertensive effects, at least in some hypertensive patients. Magnesium and possibly also calcium supplements may be effective in reducing blood pressure in some hypertensives. In hypertensive patients treated with drugs sodium restriction and potassium and magnesium supplementation enhance the therapeutic effect, reduce the number and dosage, and lessen the adverse effects of prescribed antihypertensive drugs. Hence, a fall in sodium consumption and increases in potassium and magnesium consumption are useful in preventing and treating arterial hypertension.

The crucial role of physiological Ca2+ concentrations in the production of endothelial nitric oxide and the control of vascular tone

1. The effect of varying the extracellular Ca2+ concentration on the basal and acetylcholine (ACh)-induced release of nitric oxide (NO) from the rabbit aorta was investigated by use of a superfusion bioassay system. 2. Changes between 0.5 and 2.0 mM in the concentration of Ca2+ superfusing the detector bioassay tissues or perfusing endothelium-denuded donor aortae had no effect on the tone of these tissues. 3. Increasing the concentration of Ca2+ perfusing endothelium-containing donor aortae from zero to 1.25 mM caused a transient (24 +/- 9 min), concentration-dependent basal release of NO, which was attenuated at higher concentrations of Ca2+ (1.5-2.0 mM). 4. The duration of the effect of Ca2+ on the basal release of NO was increased by a concomitant infusion of L-arginine (100 microM) through the donor aorta. 5. Changes in the concentration of Ca2+ between 0.5 and 2.0 mM had a similar biphasic effect on the release of NO induced by ACh, which was also maximal at 1.25 mM Ca2+. 6. When Ca2+ was removed from the Krebs buffer perfusing the donor aorta, the basal release of NO declined within 2 min. In contrast, the release of NO induced by ACh declined progressively over 60 min. 7. Thus changes in the concentration of Ca2+ around the physiological range modulate the synthesis of NO by the vascular endothelium and consequently, vascular tone. This may account for the effects of dietary Ca2+ supplements on the control of some hypertensive states.

Effect of increased dietary calcium on the development of reduced renal mass saline hypertension in rats

A diet fortified with calcium carbonate has been reported to reduce blood pressure in low-renin and salt-sensitive hypertensive patients. We have therefore examined the effect of increased dietary calcium on the development of reduced renal mass-saline hypertension in rats, a classical, low-renin, volume, and sodium-dependent model of hypertension. Rats with 70-75% reduction in renal mass were divided into experimental and control groups. The experimental rats were fed a sodium-free diet supplemented with calcium carbonate (2.0% calcium) and drank 1% saline for 5 weeks. Control rats consumed the salt-free diet and drank 1% saline for the same period. In control rats, as previously observed, blood pressure progressive increased from a control value of 120.0 +/- 1.2 to 174.2 +/- 1.2 mm Hg by the fifth week. In contrast, in the calcium-supplemented rats the development of hypertension was significantly attenuated; the blood pressure only increased from 117.0 +/- 1.2 to 134.0 +/- 3.8 mm Hg by the fifth week. This was associated with a 30% decrease in saline intake by the fifth week, with proportionate decreases in urine volume and sodium excretion but not potassium excretion. Urinary magnesium excretion increased. No such changes were seen in control rats. At the end of the treatment period, plasma levels of sodium, potassium, calcium, creatinine, BUN, and protein were not different, but plasma chloride and magnesium were lower in experimental rats; vascular smooth muscle cell membrane potentials were also not different. These data show that dietary calcium carbonate can attenuate the development of reduced renal mass-saline hypertension in the rat, possibly in part by altering sodium and water intake.

Dietary calcium and cell membrane abnormality in genetic hypertension

Adult stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats were maintained for 10 weeks on one of two diets: 1.0% calcium content and 2.5% calcium content. At the end of this time rats were anesthetized, and blood pressure was determined by means of aortic cannulation; then the rats were exsanguinated. Lymphocytes were isolated for determination of intracellular sodium and potassium concentrations, net sodium influx, net potassium efflux, and intracellular free calcium concentration. Serum ionized calcium was also measured. The increase in calcium content of their diet had no effect on intracellular sodium and potassium concentrations in lymphocytes from WKY rats and SHRSP. In lymphocytes from WKY rats, none of the parameters was affected by the change in dietary calcium intake. In contrast, in lymphocytes from SHRSP the increase in dietary calcium from 1.0 to 2.5% led to significant decreases in net potassium efflux (13.3 +/- 2.3 vs. 19.7 +/- 1.4 mmol/kg dry wt/hr, p less than 0.05, analysis of variance), intracellular free calcium concentration (114.5 +/- 10.2 vs. 166.2 +/- 11.2 nM, p less than 0.001), and systolic blood pressure (125.3 +/- 13.6 vs. 183.3 +/- 16.6 mm Hg, p less than 0.01). Serum ionized calcium increased in SHRSP (2.40 +/- 0.04 vs. 2.16 +/- 0.03, p less than 0.01) but not in WKY rats (2.34 +/- 0.05 vs. 2.31 +/- 0.05) fed the high calcium diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of parathyroidectomy on arterial hypertrophy, vascular lesions, and aortic calcium content in deoxycorticosterone-induced hypertension

Parathyroidectomy (Px) did not prevent the development of deoxycorticosterone (DOC)-induced hypertension inasmuch as the systolic blood pressure at 4 weeks did not differ from that of parathyroid intact, DOC-treated rats. Px, however, ameliorated the percent incidence and severity index of hypertension-induced vascular lesions in the heart and kidney. There was less hyaline change in the coronary artery and renal arteriole and fewer scars in the myocardium of Px + DOC rats than in DOC-treated animals. Arterial hypertrophy in aorta, coronary artery, renal interlobular artery, and renal arteriole in hypertensive animals was not affected by Px. The aortic content of total calcium in the Px-hypertensive rats was reduced significantly as compared to parathyroid-intact hypertensive rats. The abdominal aorta in the Px + DOC group showed a greater reduction in calcium than the thoracic aorta. We conclude that calcium may not be essential in mediating hypertension-induced vascular hypertrophy. Parathyroidectomy permitted a separation of high blood pressure-hypertrophy from hyaline vascular lesions in DOC-induced hypertensive rats, likely acting upon endothelial cells to prevent movement of plasma proteins (hyaline change) from the vascular lumen into the media-subendothelial space of blood vessels.

Salt sensitivity and systemic hypertension in the elderly

Aging in industrialized societies is accompanied by increases in the incidence and prevalence of hypertension, with a disproportionately greater increase occurring among aging blacks than among aging whites. This geriatric hypertension is generally of a salt-sensitive nature with a disproportionate frequency of isolated systolic hypertension. Although salt-taste acuity declines with age, salt sensitivity among the elderly does not appear to result from a compensatory increase in salt intake. Rather, age-related increases in salt sensitivity result, in part, from a reduced ability to appropriately excrete a salt load, which is due to a decline in renal function and to a reduced generation of natriuretic substances such as prostaglandin E2 and dopamine. Age-associated declines in the activity of membrane sodium/potassium-adenosine triphosphatase (Na/K-ATPase) may also contribute to geriatric hypertension because this results in increased intracellular sodium that may cause reduced sodium-calcium exchange and thereby increase intracellular calcium and vascular resistance. Reductions in cellular calcium efflux due to reduced calcium-ATPase activity may similarly cause an increase in intracellular calcium and vascular resistance. Increasing dietary calcium intake may represent an effective nonpharmacologic treatment for some salt-sensitive persons because it appears to reduce intracellular calcium by (1) suppressing parathyroid hormone-mediated calcium influx, (2) increasing Na/K-ATPase activity, and (3) reducing intravascular volume due to calcium-induced natriuresis.