Calcium metabolism and hypertension

Calcium Biofortification of Crops-Challenges and Projected Benefits

Despite Calcium (Ca) being an essential nutrient for humans, deficiency of Ca is becoming an ensuing public health problem worldwide. Breeding staple crops with higher Ca concentrations is a sustainable long-term strategy for alleviating Ca deficiency, and particular criteria for a successful breeding initiative need to be in place. This paper discusses current challenges and projected benefits of Ca-biofortified crops. The most important features of Ca nutrition in plants are presented along with explicit recommendations for additional exploration of this important issue. In order for Ca-biofortified crops to be successfully developed, tested, and effectively implemented in most vulnerable populations, further research is required.

Long-Term Oral Calcium Supplementation Reduces Diastolic Blood Pressure in End Stage Renal Disease. A Randomized, Double-Blind, Placebo Controlled Study

Previous studies suggest that oral calcium supply reduces blood pressure in patients with mild to moderate hypertension. The aim of this study was to determine whether oral calcium supply reduces blood pressure in patients undergoing haemodialysis. The study was randomized, double-blind, and placebo controlled. Eleven patients received two grams of calcium per day and 12 patients received placebo. Three patients (one from the calcium group and two from the placebo group) dropped out within the first month. The groups were comparable at inclusion regarding blood pressure, weight, and serum values. Blood pressure measurements were auscultatory with a mercury manometer and diastolic blood pressure was measured as Korotkoff phase V. At inclusion a significant positive correlation between serum phosphate and blood pressure was found. After a study period of six months a significant reduction in diastolic blood pressure was found between the two groups (p < 0.05), but no difference was found in systolic blood pressure. The reduction in diastolic blood pressure was 6.9 mmHg of the pretreatment level in the calcium group. In conclusion, the treatment of secondary hyperparathyroidism with oral calcium gives good benefits in the regulation of diastolic blood pressure. A well controlled phosphate homeostasis may also be of importance for the control of blood pressure in haemodialysis patients.

Serum levels of lipids, calcium and magnesium in women with hypothyroidism and cardiovascular diseases

Lipid abnormalities in hypothyroidism contribute to the disproportionate increase in cardiovascular risk. A possible relationship between serum level of magnesium (Mg) and calcium (Ca) and cardiovascular disease was recorded. In this work, the possible correlation between lipid profile components and serum cations Ca and Mg was investigated. Matched healthy women were evaluated in a cross-sectional study. All parameters were measured spectrophotometrically. The results showed a significant decrease (P < 0.05) in high-density lipoprotein-cholesterol (HDL-C), total and ionized Mg in hypothyroid patients in comparing with control group. There was a significant increase (P <0.05) in serum total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C) and (LDL-C)/(HDL-C) ratio in hypothyroid patients as compared with control group. However, no correlation was found between the cation levels and lipid profile of the studied groups. It can be concluded that patients with hypothyroidism exhibited elevated atherogenic parameters (TC and LDL-C) and high risk of cardiovascular diseases.

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.

Novel regulatory aspects of the extracellular Ca2+-sensing receptor, CaR

The capacity to sense and adapt to changes in environmental cues is of paramount importance for every living organism. From yeast to man, cells must be able to match cellular activities to growth environment and nutrient availability. Key to this process is the development of membrane-bound systems that can detect modifications in the extracellular environment and to translate these into biological responses. Evidence gathered over the last 15 years has demonstrated that many of these cell surface "sensors" belong to the G protein-coupled receptor superfamily. Crucial to our understanding of nutrient sensing in mammalian species has been the identification of the extracellular Ca(2+)/cation-sensing receptor, CaR. CaR was the first ion-sensing molecule identified in man and genetic studies in humans have revealed the importance of the CaR in mineral ion metabolism. Latter, it has become apparent that the CaR also plays an important role outside the Ca(2+) homeostatic system, as an integrator of multiple environmental signals for the regulation of many vital cellular processes, from cell-to-cell communication to secretion and cell survival/cell death. Recently, novel aspects of receptor function reveal an unexpected role for the CaR in the regulation of growth and development in utero.

Cytochrome P-450 metabolites of 2-arachidonoylglycerol play a role in Ca2+-induced relaxation of rat mesenteric arteries

The perivascular sensory nerve (PvN) Ca(2+)-sensing receptor (CaR) is implicated in Ca(2+)-induced relaxation of isolated, phenylephrine (PE)-contracted mesenteric arteries, which involves the vascular endogenous cannabinoid system. We determined the effect of inhibition of diacylglycerol (DAG) lipase (DAGL), phospholipase A(2) (PLA(2)), and cytochrome P-450 (CYP) on Ca(2+)-induced relaxation of PE-contracted rat mesenteric arteries. Our findings indicate that Ca(2+)-induced vasorelaxation is not dependent on the endothelium. The DAGL inhibitor RHC 802675 (1 microM) and the CYP and PLA(2) inhibitors quinacrine (5 microM) (EC(50): RHC 802675 2.8 +/- 0.4 mM vs. control 1.4 +/- 0.3 mM; quinacrine 4.8 +/- 0.4 mM vs. control 2.0 +/- 0.3 mM; n = 5) and arachidonyltrifluoromethyl ketone (AACOCF(3), 1 microM) reduced Ca(2+)-induced relaxation of mesenteric arteries. Synthetic 2-arachidonoylglycerol (2-AG) and glycerated epoxyeicosatrienoic acids (GEETs) induced concentration-dependent relaxation of isolated arteries. 2-AG relaxations were blocked by iberiotoxin (IBTX) (EC(50): control 0.96 +/- 0.14 nM, IBTX 1.3 +/- 0.5 microM) and miconazole (48 +/- 3%), and 11,12-GEET responses were blocked by IBTX (EC(50): control 55 +/- 9 nM, IBTX 690 +/- 96 nM) and SR-141716A. The data suggest that activation of the CaR in the PvN network by Ca(2+) leads to synthesis and/or release of metabolites of the CYP epoxygenase pathway and metabolism of DAG to 2-AG and subsequently to GEETs. The findings indicate a role for 2-AG and its metabolites in Ca(2+)-induced relaxation of resistance arteries; therefore this receptor may be a potential target for the development of new vasodilator compounds for antihypertensive therapy.

Blood pressure and calcium intake are related tobone density in adult males

Based on the premise that elevated blood pressure and low bone mass have both been associated with poor Ca nutriture and disturbances in Ca metabolism, a cross-sectional study was employed to determine if blood pressure and dietary Ca intake were significantly related to bone mass. Forty-seven men between 24–77 years of age with blood pressure values ranging from normal to mildly elevated comprised the study group. Blood pressure was measured with a random-zero sphygmomanometer. Bone mineral content (BMC) and density (BMD) of the hip, spine and total body were measured with dual-photon absorptiometry. Dietary intake and physical activity were also assessed. Multiple linear regression analysis was used for statistical analysis. After adjusting for known confounding variables (age, BMI, Ca intake, and others) diastolic blood pressure was negatively related to BMC (P ≤ 0·05) and BMD (P ≤ 0·01) of the total body, trochanteric region (P < 0·01) and Ward's triangle (P < 0·05), and to BMC of the femoral neck (P < 0·05) and lumbar spine, although the latter was just shy of statistical significance (P = 0·058). Systolic blood pressure was negatively related to trochanteric BMD (P = 0·04) and BMC (P = 0·06). Ca intake was positively related to total body BMD (P = 0·005), and BMC of the lumbar spine (P = 0·05). In this population of men, Ca intake was a positive predictor, and blood pressure was a negative predictor of regional measures of bone mass. These findings support the concept that independent of age, BMI and Ca intake, elevated blood pressure varies indirectly with bone mass and density, known predictors of osteoporotic fractures. Future studies are needed to determine whether elevated blood pressure is causally related to the development of low bone mass, and what role dietary Ca plays in that pathway.

Effect of interleukin 8 and ICAM-1 on calcium-dependent outflow of K+ in erythrocytes from subjects with essential hypertension

INTRODUCTION

The pathogenic mechanisms underlying the increase in peripheral resistance and the contraction of smooth muscular fibre cells in essential hypertension are not yet clearly understood. However, it is now known that immune system activation plays a role in the pathogenesis of some forms of arterial hypertension, and recent data show that the Ca2+ influx in some cells (i.e. red blood cells, leukocytes, platelets, smooth muscular fibre cells) is increased in subjects with essential hypertension, thus revealing a possible alteration in cellular membrane. The end-points of this study were therefore to ascertain whether red blood cells used as a cellular membrane model have a greater Ca2+ dependent K+ flow (Gardos effect) in hypertensive patients than in normotensive controls, to point out a different regulation of ionic channels, and whether IL-8 and the adhesion molecule ICAM-1 influence the membranous outflow.

MATERIAL AND METHODS

The study was conducted on 87 Caucasian subjects. Of these, 50 (25 men, 25 women; mean age 43 +/- 3 years, mean body mass index (BMI) 27 +/- 0.5 and 22.3 +/- 0.3 kg/m(2), respectively) had mild-to-moderate hypertension (mean arterial blood pressure 120 +/- 8 mmHg ). The other 37 (18 men, 19 women; mean age 39 +/- 3 years; BMI 23.8 +/- 0.5 kg/m(2) and 22.8 +/- 0.5 kg/m(2), respectively were normotensive healthy volunteers (mean arterial blood pressure 89 +/- 2 mmHg). All the patients and subjects were untreated for at least 4 weeks before blood sampling.

RESULTS

Ca2+-dependent K+ outflow was found to be greater in samples from patients with essential hypertension than in those from normotensive controls. lL-8 and ICAM-1 significantly enhanced the Ca2+-dependent K+ outflow in red blood cells from hypertensive subjects but had an inhibitory effect on cells from controls. In the experimental model, the presence of TMB-8, a membrane calcium antagonist, significantly reduced the Ca2+-dependent K+ efflux.

CONCLUSION

Vasoconstriction in subjects with essential hypertension may therefore depend on a different regulation of ionic flow that probably supports an increased Ca2+ inflow in smooth muscle fibre cells. Under certain pathological conditions, some immune system components (i.e. interleukins, adhesion molecules) may directly enhance membrane permeability to Ca2+, thus inducing vasoconstriction in the smooth muscle cells.

Renal interstitial Ca(2+)

Renal interstitial fluid Ca(2+) concentration ([Ca(2+)](isf)) was measured in anesthetized Wistar rats by using in situ microdialysis. During perfusion of 20 cm of the proximal small intestine with Ca(2+)-free buffer, renal [Ca(2+)](isf) was 1.63 +/- 0.19 mmol/l in the cortex (n = 6) and 1.93 +/- 0.12 mmol/l in the medulla (n = 5, P = 0.223). When Ca(2+) in the intestinal lumen was increased to 3 mmol/l, no change was seen in total or ionized serum Ca(2+) (S(Ca)), urinary Ca(2+) excretion (U(Ca)), or Ca(2+) in a microdialysate of the kidney cortex. Increasing intestinal Ca(2+) further, to 6 mmol/l, was without effect on S(Ca) but significantly increased U(Ca) by 38% and microdialysate Ca(2+) by 36% (1.25 +/- 0.0.09 vs. 1.70 +/- 0. 14 mmol/l, n = 4, P < 0.05). Intravenous infusion of 28 ng. kg(-1). min(-1) of parathyroid hormone for 1 h during perfusion of the intestinal lumen with 1 mmol/ Ca(2+)caused a 7-10% rise in S(Ca), a 40% fall in U(Ca), and a 32% increase in microdialysate Ca(2+) (1.32 +/- 0.13 vs. 1.74 +/- 0.13 mmol/l, n = 6, P < 0.05). Interlobar arteries with a mean diameter of 120 microm were studied by using a wire myograph to determine whether changes in extracellular Ca(2+) affect muscle tone. When precontracted with 5 micromol/l serotonin, the arteries relaxed in response to cumulative addition of Ca(2+) (1-5 mmol/l) with an ED(50) value for Ca(2+) of 3.30 +/- 0.08 mmol/l, n = 3. These data demonstrate that [Ca(2+)](isf) changes dynamically during manipulation of whole-animal Ca(2+) homeostasis and that intrarenal arteries relax in response to extracellular Ca(2+) varied over the range measured in vivo.

Benefits of dairy product consumption on blood pressure in humans: a summary of the biomedical literature

The inverse relationship between intake of dairy products and blood pressure levels was first suggested by several epidemiologic surveys in the early 1980's that revealed low calcium intake in populations with increased prevalence of hypertension. Subsequent laboratory and clinical investigations provided further evidence of the association between calcium and blood pressure, but the results of these studies were often inconsistent due to variations in study design and methods, study participants and calcium sources. The recently published results of the large and carefully executed Dietary Approaches to Stop Hypertension Study, "DASH," which demonstrated a dramatic blood-pressure lowering effect of diets rich in dairy products, fruits and vegetables, addressed many of the issues contributing to the inconsistencies in the blood pressure-calcium data. In the following review, we discuss the evolution of the scientific evidence of the association between dietary calcium intake and blood pressure, the findings and significance of the DASH trial and the consensus that now exists among health professionals regarding the importance of adequate dairy product intake for optimal blood pressure regulation.

Effect of dietary salt loading and high-calcium diet on vascular smooth muscle responses and endothelium function in rats

1. The present study examined the effects of concurrent manipulation of dietary calcium and salt on contractile responses of vascular smooth muscle (VSM) and endothelial function of aortic rings from Sprague-Dawley rats. 2. Salt loading enhanced the contractile response of the aortic rings to noradrenaline (NA), an effect that was blunted by a high calcium intake. 3. Removal of the endothelium and incubation of aortic rings in physiological salt solution containing methylene blue increased the sensitivity of the rings to NA. 4. The increase in the sensitivity of aortic rings induced by endothelium removal was more pronounced in aortic rings from salt-loaded rats. 5. Acetylcholine caused similar degrees of relaxation in all experimental groups, but the relaxation to histamine was smaller (P < 0.05) in salt-loaded rats than in other groups of rats; however, after removal of the endothelium, the contractile response to histamine was higher in salt-loaded rats. 6. The results indicate that the hypersensitivity of isolated aortic rings to agonists, as observed in salt-loaded rats, is due to altered responses of the VSM and not as a result of changes in the endothelium. In addition, salt loading tends to increase the synthesis of endothelium-dependent relaxing factor. The ability of salt loading to enhance the contractile responses of VSM to agonists can be prevented by supplementing the diet with high calcium.

Calcium-to-creatinine ratio in spot urine samples in early pregnancy and its relation to the development of preeclampsia

We investigated the relation between an alteration in calcium (Ca) excretion in early pregnancy and the risk of preeclampsia in 1,147 pregnant women. We measured Ca and creatinine (Cr) concentrations in spot urine samples obtained at 12 weeks or less of gestation. Seventy-one (6.2%) had hypertension alone, nine (0.8%) developed superimposed preeclampsia, 39 (3.4%) developed proteinuria alone, and 13 (1.1%) developed preeclampsia; 1,015 women did not develop hypertension or proteinuria. The Ca/Cr ratio was significantly reduced in the 39 women who eventually developed proteinuria (0.116 +/- .103) and 13 who developed preeclampsia (0.121 +/- .063) compared with 1,015 women who had neither hypertension nor proteinuria (0.158 +/- .239). The relative risk of development of preeclampsia, proteinuria, or superimposed preeclampsia was 1.98 (95% confidence interval, 1.22 to 3.22) for women with a Ca/Cr ratio less than the 30th percentile (0.082) compared with women with a Ca/Cr ratio greater than the 30th percentile. These results suggest that preeclampsia may be related, in part, to a relative Ca intake deficiency. Determination of the Ca/Cr ratio in spot urine samples in the first trimester is of only limited clinical value for identifying women with an increased risk of preeclampsia.

Use of dietetic-specific nutritional diagnostic codes in clinical reasoning relevant to the nutritional management of core clinical outcome indicators in hemodialysis patients

The Health Care Financing Agency (HCFA) has recommended conscientious monitoring of four core outcome indicators (anemia, albumin, treatment adequacy, and hypertension) by the end stage renal disease (ESRD) health care team. Dietetic-specific nutritional diagnostic categories (D-S NDCs) can be a powerful tool in guiding renal nutrition specialists through the clinical reasoning required to diagnose and clinically correct nutrition-related problems in hemodialysis (HD) patients. The purpose of this article is to portray one clinician's dual use of D-S NDCs to identify the nutritional problem responsible for poor performance and determine nutritionally treatable causes. Although four indicator-specific sets of D-S NDCs commonly used in the nutritional assessment of anemia, albumin, treatment adequacy and hypertension were identified and referenced, seven codes were consistently repeated. These D-S NDCs were (1) altered nutritional biochemistry integrity; (2) absence of/limited nutritional service; (3) deficit in nutrition knowledge; (4) imbalance of nutrient/fluid; (5) nutrition misinformation; (6) toxicity of nutrient/nutrient end-product; and (7) possibility of developing a specific disease. Thus, in ESRD, use of D-S NDCs shows the implicit role of the registered dietitian in disease prevention, management of altered nutrient disposition, and patient education.

Ambulatory blood pressure monitoring in renal dialysis and transplant patients

Blood pressure (BP) elevation and left ventricular hypertrophy are important factors in the high cardiovascular mortality rate in patients on the renal replacement program. Ambulatory BP monitoring is widely regarded as superior to random BP monitoring in predicting end-organ damage from elevated BP. One hundred seventeen patients (60 on hemodialysis [35 with long sessions and 25 with short sessions], 29 on continuous ambulatory peritoneal dialysis, and 28 transplant recipients) underwent ambulatory BP monitoring, with target organ assessment by electrocardiography. Mean 24-hour BP for the patients with the long hemodialysis sessions (LHD) was 115.5/66.6 mm Hg, without the regular use of antihypertensive drugs. The parathormone (PTH) level was the major determinant of BP on ambulatory BP monitoring analysis, with interdialytic weight gain and age each having weaker associations. The BPs of the other three patient cohorts were much higher (short hemodialysis session [SHD], 143.2/82.1 mm Hg; continuous ambulatory peritoneal dialysis, 137.1/76.8 mm Hg; transplant recipients, 135.9/79.2 mm Hg). Overall, two thirds of the patients had reduced diurnal BP variability. Electrocardiogram voltage criteria for left ventricular hypertrophy were exceeded in approximately one third to one half of the patients. Our findings show that good control of BP is possible without recourse to antihypertensive drugs in the context of dialysis with slow ultrafiltration.

Up-regulation of intracellular signalling pathways may play a central pathogenic role in hypertension, atherogenesis, insulin resistance, and cancer promotion--the 'PKC syndrome'

The modern diet is greatly different from that of our paleolithic forebears' in a number of respects. There is reason to believe that many of these dietary shifts can up-regulate intracellular signalling pathways mediated by free intracellular calcium and protein kinase C, particularly in vascular smooth muscle cells; this disorder of intracellular regulation is given the name 'PKC syndrome'. PKC syndrome may entail either a constitutive activation of these pathways, or a sensitization to activation by various agonists. The modern dietary perturbations which tend to induce PKC syndrome may include increased dietary fat and sodium, and decreased intakes of omega-3 fats, potassium, calcium, magnesium and chromium. Insulin resistance may be both a cause and effect of PKC syndrome, and weight reduction and aerobic training should act to combat this disorder. PKC syndrome sensitizes vascular smooth muscle cells to both vasoconstrictors and growth factors, and thus promotes both hypertension and atherogenesis. In platelets, it induces hyperaggregability, while in the microvasculature it may be a mediator of diabetic microangiopathy. In vascular endothelium, intimal macrophages, and hepatocytes, increased protein kinase C activity can be expected to increase cardiovascular risk. Up-regulation of protein kinase C in stem cells may also play a role in the promotion of 'Western' fat-related cancers. Practical guidelines for combatting PKC syndrome are suggested.

Calcium-ATPase and insulin in adolescent offspring of essential hypertensive parents

A number of abnormalities in calcium homeostasis have been reported in patients with essential hypertension. IN turn, insulin has been shown to influence the activity of the Ca(2+)-ATPase. We have previously shown that normotensive offspring of essential hypertensive individuals have an exaggerated insulin response to a glucose overload. Therefore, the aim of the present study was to evaluate basal and calmodulin-activated Ca(2+)-ATPase in red blood cells and its relationship to the insulin response during an intravenous glucose tolerance test in 27 normotensive adolescents with a family history of essential hypertension (F+) (mean age, 13.9 +/- 0.5 years) and in 10 control subjects matched for age and body mass index with no family history of hypertension (F-). The results (mean +/- SD) were as follows (mumol Pi/[mg protein/h]10(-1)): basal Ca(2+)-ATPase, 4.5 +/- 1.2 in F+ and 5.1 +/- 1.6 in F- (P = NS); calmodulin-activated Ca(2+)-ATPase, 13.6 +/- 3.9 in F+ and 16.2 +/- 1.7 in F- (P < .04). The insulin area under the curve after the glucose load was 3413 +/- 1674 microU/mL per hour in F+ and 2752 +/- 928 in F- (P = NS). Calmodulin-activated Ca(2+)-ATPase showed a negative correlation with the insulin area under the curve (r = -.59, P < .005) and cholesterol levels (r = -.38, P < .03). Urinary calcium excretion was 1.82 +/- 0.9 mmol/d in F+ and 2.47 +/- 0.9 mmol/d in F- (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Development of hypertension in spontaneously hypertensive rats: role of milk electrolytes

1. Milk samples were collected from lactating spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) normotensive females at 8, 14 or 18 days postpartum. 2. Milk samples were later analysed for content of calcium (Ca++), sodium (Na+), potassium (K+), chloride (Cl-) and total protein. 3. Milk samples from SHR females had significantly higher concentrations of Na+ (at 8 and 14 days) and Cl- and significantly lower concentrations of Ca++, K+ (at 8 and 14 days) and total protein compared to milk samples from WKY females. 4. Preweanling dietary content of several electrolytes implicated in the development of hypertension differed dramatically between SHR and WKY strains. This altered diet early in life may serve as an environmental trigger for progressive age-related increases in arterial pressure in SHR.

Augmented Ca2+ mobilization is a hypertensive trait discriminated from a 'major gene' in backcross analysis between SHR and Donryu rats

1. Blood pressure and Ca2+ mobilization were significantly greater in SHR than in Donryu and F1 rats. 2. Backcross linkage analysis between spontaneously hypertensive rats and normotensive Donryu rats was performed to dissect polygenic hypertensive traits and to detect the existence of a single 'major gene'. 3. Cluster and discriminant analysis of a scattergram of blood pressure versus Ca2+ mobilization classified the backcrossed rats into two groups. The two groups were referred to the higher group and the lower group with regard to their relative blood pressure values. 4. Blood pressure was correlated with Ca2+ mobilization in each group; the correlation coefficients were 0.41 for the higher group (P < 0.01) and 0.71 for the lower group (P < 0.0001).

Effect of calcium supplementation on blood pressure in children

OBJECTIVE

To evaluate the effect of calcium supplementation on blood pressure in children.

DESIGN

Randomized, double-masked, placebo-controlled trial.

SETTING AND PARTICIPANTS

One hundred one fifth-grade students in one inner-city school.

INTERVENTION

Each child consumed 480 ml of juice beverages, containing either no calcium or 600 mg calcium (as calcium citrate malate) daily for 12 weeks.

MEASUREMENTS

At baseline we obtained nutrient data from three sets of 2-day food records on each subject. We measured blood pressure four times on each of three weekly sittings at baseline and at follow-up. Using multiple linear regression analysis, we compared mean blood pressure change in the intervention group with that in the placebo group.

RESULTS

There were 50 girls and 51 boys; 61 subjects were black. At baseline, mean age was 11.0 years, systolic and diastolic blood pressures were 101.7 and 57.7 mm Hg, daily total energy intake was 1966 kcal, and calcium intake was 827 mg. With control for age, height, hours of television watched, and baseline blood pressure, systolic blood pressure increased 1.0 mm Hg in the intervention group and 2.8 mm Hg in the placebo group (effect estimate = -1.8 mm Hg; 95% confidence interval -4.0, 0.3). In black subjects the intervention effect estimate was -2.0 mm Hg (95% confidence interval -4.4, 0.4). From lowest to highest quartile of baseline calcium intake (per 1000 kcal), the intervention effect estimates were -3.5, -2.8, -1.3, and 0.0 mm Hg (p for trend = 0.009). There was little effect on diastolic blood pressure.

CONCLUSION

These data suggest a blood pressure-lowering effect of calcium supplementation in children, especially in subjects with low baseline calcium intake.

Calcium accumulation in experimental hypertension

At present, the significance of calcium accumulation in the aetiology of coronary artery disease (CAD) in humans is not known, except only to exacerbate the condition. In an attempt to understand ionic disturbances in vasculature derived from cardiovascular abnormalities, soft tissues from hypertensive models were examined. The study hypothesis was to see if basic cardiovascular regulatory sites in hypertensive models accumulated greater amounts of Ca2+. Calcium levels were measured by flame atomic absorption spectrophotometry in tissue derived from two types of hypertensive rabbits. Both models of hypertension developed mean arterial pressures of at least 50 mm Hg greater than those of controls over a 5-wk period. Significant increases in calcium levels were found in left ventricle and aorta derived from both hypertensive groups compared with controls. Renal cortex and medulla were not significantly different among any of the groups. These levels corroborate the findings of others which show increased calcium levels in cardiovascular tissues in experimental hypertension in rabbits. Although there have been several studies that have shown the relationship between calcium, hypertension and CAD, this is the first study to look at calcium accumulation rather that the effects of calcium channel blockers. The link between hypertension and calcium accumulation in a number of tissues may be important in the development of CAD and other cardiac dysfunction.

Multiple linear regression analysis of hypertrophy, calcium and cadmium in hypertensive and non-hypertensive states

Heart disease remains a major public health issue. In this study we aimed to achieve a greater mathematical and mechanistic understanding of the relationship between exposure to heavy metals and heart disease. Measurements of calcium and cadmium levels were made by flame atomic absorption spectrophotometry in tissue from hypertensive and non-hypertensive rabbits. Relationships between hypertrophy, calcium and cadmium were tested using multiple regression analysis. Multiple linear relationships occurred that showed the dependence of hypertrophy on calcium and cadmium levels, and of calcium accumulation on cadmium and hypertrophy. These data provide an insight into the mechanisms of heavy metal accumulation and the development of cardiovascular hypertrophy.

Prevention of preeclampsia with calcium supplementation and vitamin D3 in an antenatal protocol

OBJECTIVES

Using an angiotensin sensitivity test we carried out a prospective study in an attempt to predict the possible onset of preeclampsia and to prevent it by calcium supplementation (elemental calcium 156 or 312 mg/day per os) and treatment with vitamin D3 (0.5 micrograms/3 day per os).

METHOD

We used a study design in which 666 singleton pregnant women were managed with conventional antenatal care and 210 singleton pregnant women were managed with a protocol, together with conventional antenatal care.

RESULT

Of the 666 women managed conventionally, 113 (16.9%) developed preeclampsia. However, the incidence of preeclampsia in the 210 women managed on the protocol was lower, at 10.9%.

CONCLUSION

Our findings indicate that this protocol for the prediction and prevention of preeclampsia is useful for pregnant women at high risk of developing preeclampsia.

Micronutrient effects on blood pressure regulation

Five micronutrients have been shown to directly influence blood pressure: sodium, calcium, potassium, magnesium, and chloride. The data presented here are based on accumulated findings from epidemiologic, laboratory, and clinical investigations, many of which focused primarily on a single nutrient. However, as also discussed here, nutrients are not consumed in isolation, and their physiologic interactions and combined effects on blood pressure are the subjects of much of the current research in the area of diet and hypertension.

Hypocalcemia and pregnancy-induced hypertension produced by low-calcium diet

Recent studies from our laboratory in fasting pregnant ewes with twin gestation have implicated low serum calcium concentration in the etiology of hypertension in pregnancy. We hypothesized that the reduction in serum calcium concentration produced by feeding of a calcium-deficient diet in twin gestation would lead to a significant increase in maternal arterial blood pressure, vascular resistance, and protein in the urine and decreased uterine blood flow. Twenty-five instrumented ewes were used in the present study. After surgery a calcium-deficient diet and deionized water (calcium ion free) were provided ad libitum to 19 animals. Blood pressure, cardiac output, heart rate, and uterine blood flow were monitored every other day. Six control animals were provided with standard Rumilab diet and tap water (group 1). Animals on a low-calcium diet (group 2) were subdivided according to the blood ionized calcium response to low dietary calcium intake. Non-hypocalcemic animals were assigned to group 2a (n = 10), and hypocalcemic animals (calcium concentration below two standard deviations from the control group) were assigned to group 2b (n = 9). In group 2b calcium concentration decreased from 1.03 +/- 0.04 mmol/L on day 110 of gestation to 0.77 +/- 0.03 mmol/L by day 125 of gestation. Arterial blood pressure increased significantly from 76 +/- 2 to 91 +/- 2 mm Hg, and uterine blood flow decreased from 950 +/- 53 to 579 +/- 48 mL/min. Urinary protein increased from 1.7 +/- 0.3 to 10.5 +/- 1.2 g/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary calcium and blood pressure in experimental models of hypertension. A review

More than 80 studies have reported lowered blood pressure after dietary calcium enrichment in experimental models of hypertension. The evidence presented here suggests that dietary calcium may act concurrently through a number of physiological mechanisms to influence blood pressure. The importance of any given mechanism may vary depending on the experimental model under consideration. Supplemental dietary calcium is associated with reduced membrane permeability, increased Ca(2+)-ATPase and Na,K-ATPase, and reduced intracellular calcium. These results suggest that supplemental calcium may limit calcium influx into the cell and improve the ability of the VSMC to extrude calcium. This could be a direct effect of calcium on the VSMC or an indirect effect mediated hormonally. The calcium-regulating hormones have all been found to have vasoactive properties and therefore may influence blood pressure. Furthermore, CGRP and the proposed parathyroid hypertensive factor are both vasoactive substances that are responsive to dietary calcium. Therefore, diet-induced variations in calcium-regulating hormones may influence blood pressure. Modulation of the sympathetic nervous system is another important way that dietary calcium can influence blood pressure. There is evidence of altered norepinephrine levels in the hypothalamus as a consequence of manipulations of dietary calcium as well as changes in central sympathetic nervous system outflow. Dietary calcium has also been shown to specifically modify alpha 1-adrenergic receptor activity in the periphery. In some experimental models of hypertension, dietary calcium may alter blood pressure by changing the metabolism of other electrolytes. For example, the ability of calcium to prevent sodium chloride-induced elevations in blood pressure may be attributed to natriuresis. However, natriuresis does not account for all of the interactive effects of calcium and sodium chloride on blood pressure. Sodium chloride-induced hypertension may be due in part to calcium wasting and subsequent elevation of calcium-regulating hormones. Chloride is an important mediator of this effect because it appears that sodium does not cause calcium wasting when it is not combined with chloride. More attention to the central nervous system effects of dietary calcium is needed. Not only can calcium itself influence neural function, but many of the calcium-regulating hormones appear to affect the central nervous system. The influence of calcium and calcium-regulating hormones on central nervous system activity may have important implications for blood pressure regulation and also may extend to other aspects of physiology and behavior.

Human SA gene locus as a candidate locus for essential hypertension

We have recently identified a candidate gene for rat genetic hypertension by identifying an mRNA species that shows markedly higher expression in the kidneys of spontaneously hypertensive rats than in those of Wistar-Kyoto rats. By using a restriction fragment length polymorphism, we carried out cosegregation analyses between the genotype of the SA gene and blood pressure in three F2 cohorts and observed significant effects of the SA gene on blood pressure in all of those cohorts. In the present study, we have isolated a human counterpart of the rat SA gene to investigate the possible association between the human SA gene and human essential hypertension. The deduced amino acid sequence from the isolated human SA cDNA consisted of 578 amino acid residues and had slight homology to a bacterial enzyme, acetyl-coenzyme A synthase. The human gene was mapped to the human chromosome 16 with the use of a rodent/human somatic hybrid cell panel. A restriction fragment length polymorphism was found with the restriction enzyme Pst I, and the allele frequencies were compared between hypertensive and control groups. The hypertensive group consisted of 89 individuals, and the Pst I rare allele (A2 allele) frequency in this group was 0.270. The control group consisted of 81 healthy normotensive individuals whose precise clinical data were available; the A2 allele frequency in this group was 0.09. Significant differences in the frequency of the A2 allele were observed between the hypertensive and control groups (P = .0001). The present findings provide favorable evidence that the SA gene is a candidate gene for human essential hypertension and also provide a starting point for future studies.

Calcium and sodium handling during volume expansion in essential hypertension

To evaluate the actual role of extracellular fluid volume (ECFV) expansion per se in modulating the rate of urinary calcium excretion, a thermoneutral water immersion (WI) study was conducted in 10 normal subjects and 30 patients with essential hypertension. Central hypervolemia by 2 hours of WI caused a significant diuretic and natriuretic response (P < .005) in normal subjects; no significant changes were detected in urinary calcium and magnesium excretion. WI provoked either an appropriate or exaggerated natriuresis (P < .001) in 21 hypertensive patients; these subjects also exhibited a highly positive correlation between urinary sodium and calcium excretion during WI (P < .001). In the remaining nine hypertensive patients, WI produced a significant diuretic response, but a barely discernible (P = NS) natriuresis (inappropriate response). These subjects also exhibited a significant reduction of urinary calcium (P < .001) and magnesium (P < .01) excretion. The data indicate that (1) volume expansion per se may have a role in regulating calcium excretion in hypertensive subjects; (2) a calcium leak may be attributable to a close relationship between urinary sodium and calcium metabolism, and causally related to a disturbance of sodium and volume homeostasis in hypertension.

Comparative study of diets enriched with evening primrose, black currant, borage or fungal oils on blood pressure and pressor responses in spontaneously hypertensive rats

The effects of oils enriched with gamma-linolenic acid (GLA) on blood pressure and pressor responses were examined in spontaneously hypertensive rats (SHR). Rats were fed purified diets containing evening primrose (EPO), black currant (BCO), borage (BOR) or fungal (FGO) oils for 7 weeks. Significant reductions in blood pressure were obtained in SHR rats maintained on diets enriched with GLA oils. The antihypertensive effect was not associated with enhanced pressor responsiveness to norepinephrine or angiotensin II. Moreover, no differences were found in blood pressure responses to the calcium channel blocker, verapamil. The results suggest that GLA-enriched oils inhibit the development of hypertension in the SHR rat. The blood pressure lowering effect is not mediated by altered pressor responses to vasoconstrictor hormones or intracellular calcium mechanisms.

The role of diet in the genesis and treatment of hypertension

In this brief review, we have not been able to address all of the various dietary factors which have been implicated as causal in hypertension. Because of the heterogeneity of hypertension, it is quite difficult to find a simple answer to the question of how important dietary factors are in causing hypertension and even more difficult to answer the question of how diet should be therapeutically altered in treating a hypertensive patient. Given the difficulties in achieving good compliance to almost any dietary prescription and the lifestyle changes these therapies often require, significant benefit must be demonstrated to justify the efforts. It is worth emphasizing that many of the dietary alterations which have been proposed for treating hypertension have even better established preventative health rationales which justify their use. Although salt intake is a factor in the genesis of hypertension, the effectiveness of salt restriction varies between patients. Despite the absence of good predictors of response, moderate sodium reduction is a reasonable first step when dealing with a hypertensive patient. In obese hypertensive patients, weight loss provides a modest but significant BP reduction. Added benefit may be obtained by lowering total fat content and increasing the ratio of polyunsaturated to saturated fats. The reduction in cardiovascular risk with these changes in dietary fat, over and above the lowering of BP, make this approach appropriate in all hypertensive patients. Potassium supplementation, while sometimes effective, is more difficult to recommend broadly. Calcium supplementation is certainly reasonable in women, for whom such therapy should be seen as good dietary advice for the prevention of osteoporosis. Moderate alcohol intake probably has little deleterious effect, whereas heavy alcoholism does contribute to increased BP. Again, reduction of alcohol intake is important for reasons other than the modest BP reduction attained.

Regulation of calcium influx into vascular smooth muscle by vitamin B6

In the vitamin B6 deficiency-induced hypertensive (B6DHT) rat there is an increased influx of calcium into the vascular smooth muscle. Vitamers which possess vitamin B6 activity blocked the in vitro calcium influx into the caudal artery of B6DHT rats and the BAY K 8644-induced influx into artery segments from vitamin B6-supplemented (control) rats. BAY K 8644 did not increase further the calcium influx into caudal artery segments from B6DHT rats. However, when this influx was partly decreased by Nifedipine or by pyridoxal phosphate, BAY K 8644 antagonized their effects indicating that calcium influx mediated by the dihydropyridine-sensitive calcium channel is a site of the calcium influx defect in the B6DHT rat.

Alterations in calcium metabolism in young people at risk for primary hypertension. The Dutch Hypertension and Offspring Study

Several disturbances in calcium metabolism have been reported in primary hypertensive subjects. It is, however, not clear whether these alterations predate the development of hypertension or occur as a consequence of high blood pressure. We studied indexes of calcium metabolism in three groups of normotensive children with different familial predispositions for hypertension, based on parental blood pressure levels, with two, one, or no hypertensive parents. Plasma intact parathyroid hormone [1-84] was higher in the offspring of hypertensive parents compared with offspring of normotensive parents (difference, 0.58 pmol/L; standard error of the difference [SED], 0.24; p = 0.02). Mean serum calcium levels were slightly reduced in the offspring of two hypertensive parents (-0.019 mmol/L, SED = 0.013, p = 0.17). Plasma magnesium and phosphate levels were lower in the offspring of hypertensive parents (-0.032 mmol/L [SED = 0.016, p = 0.05] and -0.045 mmol/L [SED = 0.024, p = 0.05], respectively). Mean 1.25-dihydroxyvitamin D3 levels were similar among the groups. No differences in dietary intake of calcium, phosphate, or fiber were found. Urinary calcium excretion per 24 hours and the ratio of 24-hour urinary calcium excretion to daily calcium intake were somewhat higher in the offspring of hypertensive parents. Renal fractional excretion of calcium was similar in the offspring of two hypertensive parents, and renal fractional excretion of phosphate was lower in the offspring of two hypertensive parents compared with offspring of two normotensive parents (-1.50%, SED = 0.74, p = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Childhood prevention of essential hypertension

Childhood prevention of essential hypertension requires knowledge of alterable determinants of blood pressure in children; these include obesity and sodium intake and perhaps physical activity and intake of potassium and calcium. Altering these determinants may involve two general preventive strategies. The first is a population strategy, which attempts to lower blood pressure (or keep it from rising) among all children. Population strategies may require educating children to active participants in changing their behaviors (active approach) or may merely change their environment (passive approach). The second general strategy aims to focus on children at high risk of developing hypertension as adults. To determine the usefulness of this high-risk strategy, more information is needed about prediction of adult blood pressure from childhood values and about the efficacy of interventions to control blood pressure levels in high-risk children.

Development of a technique for in situ studies of calcium absorption in the intestine of rats

The aim of the present study was to develop (feasibility, reliability, reproducibility) a technique for the in situ measurement of intestinal calcium absorption in the rat. An intestinal loop (duodenum+proximal jejunum) was perfused both by the intraluminal and vascular routes. A solution of NaCl 155 mM and CaCl2 1.25 mM containing 45Ca was perfused intraluminally at a flow rate of 0.2 ml/min and the 45Ca appearing in the venous effluent was determined to estimate calcium absorption. This technique was used to study the effect of a 10-day period of calcium supplementation on calcium absorption. The animals received enterally either 5 or 30 mg/day per kg BW. The results showed that intestinal calcium transport was enhanced when rats were given the calcium supplement for 10 days prior to the experiment (99.3 +/- 2.5 (n = 5) versus 36.6 +/- 3.6 (n = 5) nmol/min per kg BW, P < 0.001). This study indicates that dietary calcium supplement enhances calcium absorption probably by increasing the passive transport of calcium in the small intestine.

Alterations in cellular calcium handling as a result of systemic calcium deficiency in the developing chick embryo: II. Ventricular myocytes

We have previously shown that cardiovascular anomalies, such as hypertension and tachycardia, develop in Ca(2+)-deficient, shell-less (SL) chick embryos cultured ex ovo, accompanied by elevated circulating catecholamines and higher alpha-adrenergic sensitivity of cardiovascular functions. Results described in the preceding work, using erythrocytes as an experimental system, show that cellular Ca2+ handling properties are also altered as a result of long-term calcium deficiency. To examine the relevance of these findings to cells of the cardiovasculature, we have analyzed and compared the Ca2+ handling characteristics of the heart cells of SL and normal (NL) embryos. For this study, isolated and cultured ventricular myocytes of SL and NL embryos were loaded with Fura-2 via transient membrane damage with glass beads. Compared to Fura-2/AM, bead loading yielded similar values and kinetic profiles of [Ca2+]i-dependent differential fluorescence and, in addition, did not affect cell viability and beating activity. The Fura-2 loaded ventricular myocytes were washed in Ca(2+)-free buffer and then analyzed by ratiometric fluorescence (350 nm/380 nm) microscopy for kinetic changes in [Ca2+]i (R350/380 values) as a function of [Ca2+]o and adrenergic modifiers. At 0.5 and 1.0 mM [Ca2+]o, SL cells showed significantly higher [Ca2+]i, higher beating rates, and faster rate of increase in [Ca2+]i compared to NL cells. At higher [Ca2+]o (3.5 mM), there was no significant difference in [Ca2+]i and beating rate between NL and SL cells. Treatment with norepinephrine (NE; 0.01-1 microM) at 1 mM [Ca2+]o substantially increased [Ca2+]i in both NL and SL cells. In the former, the NE effect was completely inhibited by beta-blockade (1 microM propranolol). In contrast, in SL cells, NE remained effective after beta-blockade, and combined alpha-blockade (1 microM prazosin) and beta-blockade was needed to inhibit completely the NE effect. In both NL and SL cells, treatment with NE substantially increased beating rates in a similar manner. Taken together, these findings suggest that Ca2+ handling and adrenergic regulation of the heart cells are significantly altered in the SL embryos, and that these alterations may be related to the development of impaired cardiovascular functions resulting from systemic Ca2+ deficiency.

Alterations in cellular calcium handling as a result of systemic calcium deficiency in the developing chick embryo: I. Erythrocytes

Chick embryos rendered calcium (Ca) deficient by shell-less (SL) culture develop hypertension and tachycardia. Since hypocalcemia is accompanied by hypernatremia systemically but not by lower cellular Ca (Koide and Tuan, 1989), we speculate that cellular Ca handling may be altered in the SL embryo, perhaps involving Na transport. Using erythrocytes (RBC) from day-14 SL and normal (NL) embryos as the experimental cell, cellular Ca handling was studied under varying extracellular osmotic and ionic conditions by analyzing 45Ca uptake and cell volume regulation. Two agents, p-chloromercuriphenylsulfonate (PCM), and inosine/iodoacetamide (INI) were used to treat the RBCs to modify plasma membrane ion permeability and to deplete cellular ATP, respectively. Other cellular functions and activities related to Ca homeostasis, including ATP content and Ca(2+)-ATPase activity, were also analyzed. These analyses showed: (1) in NaCl, Ca uptake was similar in NL and SL cells, except after INI treatment, which resulted in slower Ca uptake by the SL cells, (2) in choline and sucrose, Ca uptake by SL RBCs was higher, (3) Ca uptake by RBCs of both embryos changed depending on the osmotic agent (Na < K < or = choline < sucrose), (4) Ca(2+)-ATPase activity was higher in SL RBC, although there was no change in the size or charge of the enzyme, and (5) in any osmotic agent, cellular Na was significantly lower, whereas cellular K was higher, in SL RBC. Based on these results, three features of RBC Ca handling were apparent: (1) Na-Ca exchange was functional and was more active in SL RBCs, (2) Ca uptake was dependent on the total ionic electrochemical gradient but not on bulk H2O movement, and (3) Ca pumping out capacity was directly correlated with Ca(2+)-ATPase activity. Elevated Ca uptake in sucrose-treated SL RBC is therefore indicative of its greater ion permeability. Taken together, these findings indicate that cellular Ca handling of the RBCs of SL chick embryos is characterized by a more active Na-Ca exchange system, greater ion permeability, and higher Ca pumping out capacity, thereby suggesting an up-regulated Ca handling function in the SL RBCs. The abnormal cellular Ca handling may be a direct result of the systemic Ca deficiency of the SL chick embryo and may be functionally related to its hypertension and tachycardia.

Effect of treatment with vitamin D3 on the responses of the duodenum of spontaneously hypertensive rats to bradykinin and to potassium

1. The diet of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) and Wistar (NWR) rats was supplemented with either 2% calcium lactate in the drinking water or 12.5 micrograms vitamin D3 100 g-1 body weight daily by gavage, for 14 days. 2. The blood pressure of the SHR treated with either calcium or vitamin D decreased to the same levels as that of WKY and NWR. 3. The response to bradykinin of the SHR isolated duodenum, which is predominantly contractile, upon treatment with vitamin D (but not with calcium), became predominantly relaxant, approaching the normal behavior of the WKY and NWR duodenum. 4. The relaxant responses of the SHR and WKY duodenum to potassium were smaller than those of NWR, but treatment with vitamin D increased the response in all three rat strains. 5. It is concluded that, besides sharing the hypotensive effect of calcium, vitamin D treatment of SHR has an effect on the duodenum smooth muscle which might be due to calmodulin-dependent activation of calcium-dependent potassium channels.

Control of the erythrocyte free Ca2+ concentration in essential hypertension

Since Ca2+ ions seem to directly participate in the control of erythrocyte membrane structure and deformability and because cell Ca2+ metabolism has been repeatedly proposed to be modified in hypertension, the intracellular calcium ion concentration ([Ca2+]i) was investigated in red blood cells from hypertensive and normotensive subjects. [Ca2+]i was measured by using the fluorescent Ca2+ chelator fura-2. Red blood cell [Ca2+]i was increased in hypertensive compared with normotensive subjects in the whole population and further increased when hypertensive were compared with age-matched normotensive subjects. An inverse relation between age and [Ca2+]i was observed when calculated with blood pressure adjusted. In hypertensive patients, high [Ca2+]i values were associated with a reduced erythrocyte deformability. The initial rate of 45Ca2+ uptake did not differ between the two blood pressure groups. Similarly, when the extracellular Ca2+ concentration was elevated from 1 to 2 mmol/l, [Ca2+]i increased by 16 +/- 4% (p less than 0.03) in red blood cells from both groups, thus maintaining a significant difference between hypertensive and normotensive subjects. Under these conditions, the addition of 10(-7) mol/l nicardipine, a dihydropyridine Ca2+ antagonist, decreased [Ca2+]i by 15 +/- 4% (p less than 0.05) and 7 +/- 5% in erythrocytes from hypertensive and normotensive subjects, respectively, thereby reducing the difference in [Ca2+]i observed between these two groups. This nicardipine effect was positively correlated to the initial [Ca2+]i. In the presence of 5 mumol/l W7, a calmodulin antagonist, [Ca2+]i increased significantly only in erythrocytes from hypertensive patients (26 +/- 6%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

[Evaluation of dietary intake of calcium in adult subjects with idiopathic arterial hypertension]

The calcium-intake relationship with other alimentary and anthropometric variables was investigates in a group of 60 adult (19-75 year-old) subjects, 50 females and 10 males, with essential arterial hypertension (DAP > 90 mmHg). The calcium intake was assessed by three different protocols: 24-hour food intake recall, food-frequency questionnaire and 3 day self-food intake register, repeated along with anthropometric measurements on three different occasions (2-15 month-intervals). The calcium intake assessed by the three methods, as well as the anthropometric data, were statistically similar on all three occasions. The mean data were then compared with those form the control, composed of 75 healthy subjects matched with the hypertensive group by age and sex. The patients ingested less calcium (mean +/- SD) than the controls on the daily (517 +/- 271 x 740 +/- 353 mg/d) and body-weight (8.1 +/- 5.0 x 11.4 +/- 5.9 mg/kg/d) basis. Among the males the calcium intake was the only difference found between groups and could be attributed to the lower intake of calcium-rich foods. The hypertensive females showed also higher lean-body mass (Body-mass index and arm muscle circumference). Thus the calcium intake discriminated both groups being associated with changes in other nutritional parameters only in females.

Effect of high calcium diet on the development of high blood pressure in intact spontaneously hypertensive rats and in adrenalectomized spontaneously hypertensive rats treated with aldosterone

The current investigation was designed to study the effect(s) of high calcium diet on the development of high blood pressure (BP) in both young intact spontaneously hypertensive rats (SHRs) and in young adrenalectomized (ADX) male SHRs treated with aldosterone (ALDO). Weaned SHRs were fed either a control calcium diet (0.5% Ca as PO4) (CCaDiet), a high calcium diet (2.5% Ca, 0.5% as PO4 and 2% as CO3) (HCaDiet), or Agway ProLab rat food containing 2.5% Ca (HCaPLDiet). The HCaDiet significantly blunted the development of high BP in young intact SHRs (P less than 0.001; n = 8 to 10). At 6 weeks of age, BP was 117 +/- 2 mm Hg (HCaDiet) compared with 135 +/- 3 mm Hg (CCaDiet); by 12.7 weeks of age, BP was 192 +/- 4 mm Hg (HCaDiet) compared with 233 +/- 3 mm Hg (CCaDiet). Similar results were observed in age-matched SHRs fed the HCaPLDiet. The results show that subcutaneous infusion of ALDO (1.0 microgram/d, osmotic pumps) for 2 weeks to young ADX male SHRs raised on the CCaDiet caused a significant increase in systolic BP when compared with SHRs implanted with Sham pumps (P less than 0.001). High BP associated with ALDO infusion was attenuated by the HCaDiet (BP after 2 weeks was 138 +/- 8 mm Hg for the HCaDiet group compared with 200 +/- 5 mm Hg for the CCaDiet group, P less than 0.001; n = 4 to 6). The results show that the HCaDiet blunts the development of high BP in intact SHRs and may protect against the development of ALDO hypertension in ADX young SHRs.