Parathyroid hormone, platelet calcium, and blood pressure in normotensive subjects

The relationship between serum 25-hydroxy vitamin D and blood pressure and quality of life in overweight and obese patients with type 2 diabetes mellitus compared with healthy subjects

Background:

Vitamin D is one of the known lipoprotein hormones with metabolic properties. We aimed to determine the serum 25-hydroxy vitamin D concentration in overweight/obese subjects with diabetes mellitus type Ⅱ (DM Ⅱ) in association with systolic and diastolic blood pressure and quality of life compared with healthy participants.

Methods:

The current case-control study was carried out among 80 overweight/obese subjects with DM Ⅱ, and 77 healthy subjects matched by sex, age and body mass index (BMI). Serum 25-hydroxyvitamin D concentration was measured by ELISA method. In order to examine the quality of life, the Persian version of SF36 questionnaire was used.

Results:

There was significant difference between diabetic and healthy subjects considering serum 25-hydroxyvitamin D concentration (p=0.012). Serum 25-hydroxyvitamin D concentration was inversely correlated with diastolic blood pressure (p=0.02) and positively associated with physical function (p<0.001), social function (p<0.001) and general health (p<0.001) components of quality of life in diabetic subjects and physical health sub-scale (p=0.004) in all participants.

Conclusion:

Serum 25-hydroxyvitamin D concentration was significantly lower in diabetic subjects in comparison with healthy controls. There was a significant reverse relationship between serum concentrations of 25-hydroxyvitamin D with diastolic blood pressure and on the other hand, a significant positive relationship with physical function, social function and general health components and physical health subscale of quality of life in participants with DM Ⅱ.

The Association between Serum 25(OH)D Status and Blood Pressure in Participants of a Community-Based Program Taking Vitamin D Supplements

Background: Vitamin D deficiency is a risk factor for hypertension. Methods: We assessed 8155 participants in a community-based program to investigate the association between serum 25-hydroxyvitamin D (25(OH)D) status and blood pressure (BP) and the influence of vitamin D supplementation on hypertension. Participants were provided vitamin D supplements to reach a target serum 25(OH)D > 100 nmol/L. A nested case-control study was conducted to examine the effect of achieving physiological vitamin D status in those who were hypertensive and not taking BP-lowering medication, and hypertensive participants that initiated BP-lowering medication after program entry. Results: At baseline, 592 participants (7.3%) were hypertensive; of those, 71% were no longer hypertensive at follow-up (12 ± 3 months later). There was a significant negative association between BP and serum 25(OH)D level (systolic BP: coefficient = −0.07, p < 0.001; diastolic BP: coefficient = −0.1, p < 0.001). Reduced mean systolic (−18 vs. −14 mmHg) and diastolic (−12 vs. −12 mmHg) BP, pulse pressure (−5 vs. −1 mmHg) and mean arterial pressure (−14 vs. −13 mmHg) were not significantly different between hypertensive participants who did and did not take BP-lowering medication. Conclusion: Improved serum 25(OH)D concentrations in hypertensive individuals who were vitamin D insufficient were associated with improved control of systolic and diastolic BP.

Serum parathyroid hormone levels predict coronary heart disease: the Tromsø Study

BACKGROUND

Primary hyperparathyroidism (PHPT) is associated with hypertension, coronary atherosclerosis and other cardiovascular diseases. We aimed to evaluate serum parathyroid hormone (PTH) levels as an independent risk factor for coronary heart disease (CHD) in subjects with serum calcium within the reference range.

DESIGN

Population-based cross-sectional study.

METHODS

The Tromsø Study was attended by 27159 subjects aged 25-79 years. Serum PTH was measured in 3570 subjects. They all completed a questionnaire on medical history, including questions on angina pectoris and myocardial infarction along with a food-frequency questionnaire. A total of 1459 men and 1753 women with serum calcium 2.20-2.60 mmol/l, serum creatinine<121 micromol/l and who did not use diuretics were included in the present study. Linear regression was used to reveal associations between PTH, age, body mass index, serum calcium, calcium intake, cholesterol, blood pressure, glycosylated haemoglobin (HbA1c) and smoking status. A logistic regression model was used to find the independent predictors of CHD.

RESULTS

When stratified for age the rate of CHD was higher in the subjects with serum PTH > 6.8 pmol/l than in those with normal or low serum PTH levels [relative risk 1.67, 95% confidence interval (CI) 1.26-2.23 in men and 1.78, 95% CI 1.22-2.57 in women]. The highest PTH quartile (> 3.50 pmol/l in men and > 3.30 pmol/l in women) predicted CHD, with odds ratios of 1.70 (95% CI 1.08-2.70) for men and 1.73 (95% CI 1.04-2.88) for women, versus the lowest PTH quartile (< 1.90 pmol/l for men and <1.80 pmol/l for women).

CONCLUSIONS

Serum PTH predicts CHD in subjects with calcium levels within the reference range. This may indicate a role for PTH in the development of CHD.

Mortality associated with primary hyperparathyroidism

561 patients with primary hyperparathyroidism were followed between 1961 and 1994. Relative survival was compared to that of the Australian population studied during the same time interval. Mortality was significantly greater in the hyperparathyroid population (P<0.001). Mortality was not greater in the patients with serum calcium levels >3.00 mmol/L compared to those with a serum calcium levels <3.00 mmol/L. 113 patients did not have parathyroid surgery. Their relative survival was not significantly different from those who had surgery but their mean serum calcium and parathyroid hormone (PTH) levels were significantly lower than those who had surgery. A re-analysis of the 453 patients followed between 1972 and 2011 was carried out and a 20-year survival analysis made of those diagnosed between 1972 and 1981 and those diagnosed between 1982 and 1991. The latter group had significantly worse relative mortality than the former group (P<0.001) but was significantly older at the time of diagnosis (56.94 ± 14.83 vs 52.01 ± 13.58, P<0.001). The serum calcium and serum PTH levels were not significantly different between these two groups.

Association of calcium concentration with pulse pressure in older women: data from a large population-based multicentric study

OBJECTIVE

High arterial pulse pressure is a predictor of cardiovascular morbimortality. Mineral metabolism has been associated with blood pressure regulation. Our objective was to determine which variable among serum calcium, parathyroid hormone and 25-hydroxyvitamin D concentrations, was associated with pulse pressure among older adults.

DESIGN

Cross-sectional study corresponding to the baseline assessment of the EPIDOS study.

SETTING

Five French cities including Amiens, Lyon, Montpellier, Paris and Toulouse.

PARTICIPANTS

Randomized sample of 610 community-dwelling older women (mean age 80.2±3.5years) using no antihypertensive drugs.

MEASUREMENTS

Serum calcium, parathyroid hormone and 25-hydroxyvitamin D concentrations; supine pulse pressure after 15 minutes of rest (hypertension defined as pulse pressure >50mmHg). Age, body mass index, the number of morbidities and of drugs daily taken, diabetes mellitus, dysthyroidy, the use of estrogenic drugs, smoking, alcohol consumption, practice of a regular physical activity, creatinine clearance, and the effects of season and study centers were used as potential confounders.

RESULTS

Hypertensive participants (n=539) had higher calcium concentrations than normotensive ones (94.33±4.12mg/L versus 93.28±3.36mg/L respectively, P=0.040). There were no between-group differences for serum parathyroid hormone and 25-hydroxyvitamin D concentrations. The multiple logistic regressions examining the serum calcium, parathyroid hormone and 25-hydroxyvitamin D concentrations as predictors of hypertension found an association only with calcium (adjusted odds ratio=1.19, P=0.015), but not with parathyroid hormone (adjusted OR=1.01, P=0.349) or 25-hydroxyvitamin D concentration (adjusted OR=0.99, P=0.971).

CONCLUSION

Increased serum calcium concentration was independently and positively associated with high pulse pressure in our study, possibly due to increased arterial stiffness. Interventions aimed at normalizing calcaemia may be attractive to prevent hypertension and cardiovascular risk in older adults.

Vitamin D, parathyroid hormone, and blood pressure in the National Health and Nutrition Examination Surveys

BACKGROUND

Previous research shows serum 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH) are each associated with blood pressure (BP), but it is unclear whether these associations are independent.

METHODS

Cross-sectional data from the US National Health and Nutrition Examination Surveys (NHANES) during 2003-2006. Analyses were restricted to 7,561 participants aged ≥20 years with measurements of 25(OH)D, PTH, BP, BP treatment, smoking, physical activity, serum calcium, and creatinine. Results were adjusted for these plus demographic variables.

RESULTS

Serum 25(OH)D was more strongly associated (inversely) with systolic than diastolic BP. Adjusted mean (standard error) difference in BP for the lowest 25(OH)D quintile (≤13 ng/ml) was 3.5 (0.7) mm Hg for systolic BP and 1.8 (0.6) mm Hg for diastolic BP, compared with the highest quintile (≥30 ng/ml). In contrast, PTH was positively associated with both systolic and diastolic BP (P < 0.0001). Adjusted mean (standard error) difference in BP for the highest PTH quintile (≥59 ng/l) was 5.9 (0.8) mm Hg for systolic BP and 4.5 (0.5) mm Hg for diastolic BP, compared with the lowest quintile (≤27 ng/l). When both 25(OH)D and PTH were included in the same model, the associations of PTH with systolic and diastolic BP were unchanged. However, the associations between 25(OH)D and BP were attenuated, with mean (standard error) difference between the highest and lowest quintiles being 2.2 (0.6) mm Hg for systolic BP (P < 0.01) and 0.8 (0.6) mm Hg for diastolic BP.

CONCLUSION

PTH may mediate most of the association between 25(OH)D and BP, which was not significant when also adjusting for body mass index.

Effect of successful parathyroidectomy on 24-hour ambulatory blood pressure in patients with primary hyperparathyroidism

OBJECTIVE

The pathogenesis of hypertension in patients with primary hyperparathyroidism (PHPT) is unclear, and the prevailing opinion is that parathyroidectomy does not affect the blood pressure (BP). Most previous studies have been based on BP measurements at rest in a clinical setting. The aim of this study was to get additional information by 24-hour ambulatory measurements.

DESIGN AND PATIENTS

Forty-nine consecutive patients with PHPT (age 63+/-12 years, 44 women) were examined before and 6 months after curative parathyroid surgery.

MEASUREMENTS

Serum concentrations of calcium and PTH, and 24-hour ambulatory mean, minimum, and maximum systolic (S) and diastolic BP, and mean arterial BP.

RESULTS

On average, the patients showed no BP change after parathyroidectomy. However, those with a history of hypertension (n=20) showed generally increased BP values after parathyroidectomy, with significantly increased minimum and average SBP (P=0.02 and P=0.04, respectively), whereas patients without a history of hypertension (n=29) showed unchanged or slightly reduced BP values after parathyroidectomy, with significantly decreased maximum SBP (P=0.04). Serum concentrations of PTH and calcium were not significantly related to any of the BP variables measured.

CONCLUSIONS

The novel finding that patients with both PHPT and hypertension may show increased BP after parathyroidectomy warrants intensified BP control postoperatively in these patients, and motivates early treatment of PHPT in order to prevent the development of complicating hypertension.

The relationship between blood pressure and serum parathyroid hormone with special reference to urinary calcium excretion: the Tromsø study

The aim of the present cross-sectional epidemiological study from Tromsø, Northern Norway, was to evaluate the relation between blood pressure and serum PTH, and to examine whether this relation can be explained by a blood pressure-induced increase in urinary calcium. Ten thousand-four hundred and nineteen subjects were invited to participate and 8,128 attended. Those with serum calcium outside the reference range (2.20-2.60 mmol/l), with increased serum creatinine (upper limit 120 micromol/l for men and 100 micromol/l for women) and those using antihypertensive medication were excluded. Three thousand- six hundred and twenty subjects had complete data on outcome measures. Height, weight, blood pressure, serum calcium, PTH, and creatinine were measured and smoking status recorded. A morning urine sample was collected and urinary calcium, sodium and creatinine measured. The urinary calcium/urinary creatinine ratio (Uca/Ucr) and urinary sodium/urinary creatinine ratio (Una/Ucr) were calculated. There was a significant association between both systolic and diastolic blood pressure and serum PTH. The Uca/Ucr increased with increasing blood pressure. However, the Uca/Ucr did not affect the association between blood pressure and serum PTH in a multiple linear regression model. The relationship between blood pressure and serum PTH was also seen in subjects with similar Uca/Ucr, and a negative association between serum PTH and the Uca/Ucr was found. In conclusion, blood pressure and serum PTH are associated. This association cannot be explained by the urinary calcium excretion alone.

Effects of a short-term vitamin D(3) and calcium supplementation on blood pressure and parathyroid hormone levels in elderly women

Calcium supplementation is effective in reducing blood pressure in various states of hypertension, including pregnancy-induced hypertension and preeclampsia. In addition, calcitropic hormones are associated with blood pressure. The hypothesis is that short-term therapy with calcium and vitamin D(3) may improve blood pressure as well as secondary hyperparathyroidism more effectively than calcium monotherapy. The effects of 8 weeks of supplementation with vitamin D(3) (cholecalciferol) and calcium on blood pressure and biochemical measures of bone metabolism were studied. The sample consisted of 148 women (mean +/- SD age, 74 +/- 1 yr) with a 25-hydroxycholecalciferol (25OHD(3)) level below 50 nmol/L. They received either 1200 mg calcium plus 800 IU vitamin D(3) or 1200 mg calcium/day. We measured intact PTH, 25OHD(3), 1,25-dihydroxyvitamin D(3), blood pressure, and heart rate before and after treatment. Compared with calcium, supplementation with vitamin D(3) and calcium resulted in an increase in serum 25OHD(3) of 72% (P < 0.01), a decrease in serum PTH of 17% (P = 0.04), a decrease in systolic blood pressure (SBP) of 9.3% (P = 0.02), and a decrease in heart rate of 5.4% (P = 0.02). Sixty subjects (81%) in the vitamin D(3) and calcium group compared with 35 (47%) subjects in the calcium group showed a decrease in SBP of 5 mm Hg or more (P = 0.04). No statistically significant difference was observed in the diastolic blood pressures of the calcium-treated and calcium- plus vitamin D(3)-treated groups (P = 0.10). Pearson coefficients of correlation between the change in PTH and the change in SBP were 0.49 (P < 0.01) for the vitamin D(3) plus calcium group and 0.23 (P < 0.01) for the calcium group. A short-term supplementation with vitamin D(3) and calcium is more effective in reducing SBP than calcium alone. Inadequate vitamin D(3) and calcium intake could play a contributory role in the pathogenesis and progression of hypertension and cardiovascular disease in elderly women.

Parameters of lymphocyte Na+-Ca2+ regulation and blood pressure: the gender effect

Alterations in cellular Ca2+ and Na+ regulation play a role in the pathogenesis of essential hypertension. Using peripheral lymphocytes from 68 normal persons, we observed the following relationships for major cellular Ca2+ regulatory parameters. Among men and women, Na+-Ca2+ exchanger activity was positively correlated with the resting cytosolic free Ca2+ ([Ca2+]c) (r=0.43, P=0.0003), and the resting [Ca2+]c was positively correlated with cytosolic Na+ ([Na+]c) (r=0.50, P=0.0001). For men only, store-operated Ca2+ entry was positively correlated with Na+-Ca2+ exchanger activity (r=0.63, P=0.0001). In addition, systolic and diastolic blood pressures were positively correlated with [Na+]c in men (r=0.53, P=0.001, and r=0. 41, P=0.017, respectively) but not in women (r=0.30, P=0.088, and r=0.24, P=0.17, respectively). Some of the relationships between cellular and blood pressure parameters were confounded by serum triglycerides. These observations indicate a gender effect on cellular Ca2+-Na+ regulation and its relationship with blood pressure.

Ca2+ in the dense tubules: a model of platelet Ca2+ load

In this work, we explored the relationship between the freely exchangeable Ca2+ (FECa2+) in the dense tubules (DT) and the sarco(endo)plasmic reticulum (SER) Ca2+-ATPase (SERCA) in circulating human platelets and examined the relationship between blood pressure (BP) and these platelet parameters. Studying platelets from 32 healthy men, we showed that the maximal reaction velocity (Vmax) of the SERCA significantly correlated with FECa2+ in the DT and with the protein expressions of SERCA 2 and 3. BP positively correlated with both the Vmax of the SERCA (r=.462, P=.010) and the FECa2+ sequestered in the DT (r=.492, P=.005). The relationships between these platelet Ca2+ parameters and BP were in part confounded by increased levels of serum triglycerides and diminished HDL cholesterol with a higher BP. No correlation was observed between the resting cytosolic Ca2+ and BP. Collectively, these findings indicate that (1) an increase in the cellular Ca2+ load in platelets is expressed by a higher activity of the SERCA and an increase in the expressions of SERCA 2 and 3 proteins, coupled with an increase in the FECa2+ in the DT, and (2) a higher BP is associated with an increase in platelet Ca2+ load in human beings, expressed by a rise in the FECa2+ in the DT and the upregulation of SERCA activity.

Relationship between serum parathyroid hormone levels in the elderly and 24 h ambulatory blood pressures

BACKGROUND

An association between serum parathyroid hormone (PTH) levels in normotensive elderly subjects and blood pressure values had been reported.

OBJECTIVE

To examine the relationship between PTH levels and other biochemical markers of calcium metabolism in elderly subjects and 24 h ambulatory blood pressures.

METHODS

We performed 24 h ambulatory blood pressure recordings for 123 independent elderly subjects aged 63-88 years using a SpaceLabs 90207 recorder. Mean night-time blood pressures were calculated from the average of readings during sleep; mean daytime blood pressures were calculated from the remaining recordings. Demographic data and details concerning the alcohol consumption and medication usage of the subjects were recorded. Serum PTH, 25-hydroxy-vitamin D, albumin, renin, aldosterone, noradrenaline, creatinine and calcium levels were measured.

RESULTS

Fifty-five patients were being administered antihypertensive therapy. Serum PTH levels correlated to the nocturnal systolic blood pressure (SBP; beta = 0.29, P = 0.002), nocturnal diastolic blood pressure (DBP), daytime SBP and mean 24 h SBP on univariate and multivariate analysis. Aldosterone levels were related to nocturnal SBP in univariate analysis (beta = 0.21, P = 0.02) but the relationship was weakened when PTH levels were included in the analysis (beta = 0.16, P = 0.09). Nocturnal, daytime and mean 24 h blood pressures were not significantly related to serum calcium, 25-hydroxy-vitamin D, age, body mass index and alcohol consumption. Sex was a significant predictor of the DBP, men having higher levels than did women (daytime DBP beta = 0.29, P = 0.001).

CONCLUSIONS

Serum PTH levels are related strongly to the blood pressure, particularly the nocturnal blood pressure in the elderly. It is not known whether PTH levels are a consequence or a cause of the elevation in blood pressure.

Cytosolic Ca profile of resting and thrombin-stimulated platelets from black women with NIDDM

In this study, human platelets were used as a cellular model for exploring cytosolic free Ca (Cai) regulation in non-insulin-dependent diabetes mellitus (NIDDM). Cai levels were monitored in resting and thrombin-stimulated platelets from obese females with NIDDM; obese, nondiabetic women, and nonobese, nondiabetic women. All subjects were black. Significant and marked elevation of basal Cai levels was observed in platelets from the diabetic subjects when no aspirin was used during platelet isolation. However, no significant differences were observed in Cai between aspirin-treated platelets from women with NIDDM and platelets from nondiabetic women. The rate of the Cai return to basal level after thrombin stimulation was significantly lower in platelets from the diabetic subjects, suggesting an abnormality in platelet Ca extrusion or sequestration in NIDDM. Platelet Cai levels positively correlated with low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio (LDL/HDL) and fasting blood glucose. These findings suggest abnormalities in platelet Cai homeostasis in NIDDM that are influenced by the serum lipid profile and perhaps glucose.

Increased calcium stores in platelets from African Americans

Differences in cation transport have been observed between African Americans and whites. These differences may underlie the increased predisposition of African Americans to essential hypertension. To further explore these racial differences, we used platelets as a cellular model for calcium regulation. We measured 45Ca fluxes in platelets from 21 African American and 25 white men. Additionally, using fura 2, we measured cytosolic free calcium levels in resting platelets and platelets treated with ouabain and thrombin. Platelet 45Ca uptake was described by two exchangeable pools: a small, rapidly exchangeable pool and a larger, slowly exchangeable pool. Both pools were larger in platelets from African Americans than from whites (263 versus 185 pmol per 1 x 10(8) platelets for the rapidly exchangeable pool, P < .05; 744 versus 532 pmol per 1 x 10(8) platelets for the slowly exchangeable pool, P < .01). 45Ca washout was described by a rapidly exchangeable pool and a static pool. The former was also higher in platelets from African Americans than from whites (246 versus 202 pmol per 1 x 10(8) platelets, P < .01). The cytosolic free calcium concentrations in resting platelets were lower in African Americans than in whites. After treatment with ouabain and thrombin, the sustained posttransient levels of cytosolic free calcium increased to a greater extent in platelets from African Americans (46.7 nmol/L) than from whites (34.5 nmol/L, P = .033). Platelets from African Americans demonstrate higher intracellular calcium stores than platelets from whites. This racial difference could explain the sensitivity of African Americans to vasoactive agents acting through calcium mobilization from intracellular stores and cytosolic calcium.

Serum intact parathyroid hormone in a random population sample of men and women: relationship to anthropometry, life-style factors, blood pressure, and vitamin D

Intact parathyroid hormone (PTH) in serum was determined in a random population sample and was related to age, sex, body composition, life-style factors, blood pressure, blood lipids, plasma fibrinogen, and serum IGF-1, osteocalcin, and vitamin D. Within the framework of the WHO MONICA Project in the city of Göteborg, Sweden, 181 men and 166 women aged 25-64 years were studied. Intact PTH concentrations varied with age but were similar in both sexes (range 4-82 ng/liter) [mean (+/- SD) 23.8 +/- 10.4 ng/liter in men and 25.1 +/- 10.6 ng/liter in women]. Intact PTH concentrations increased with increasing age, body mass index, systolic blood pressure, and 1,25(OH)2D3 and decreased with increasing 25(OH)D3 in all subjects. Additionally, in men, intact PTH correlated positively to diastolic blood pressure and negatively to coffee consumption. In women, PTH also correlated negatively to smoking and IGF-1. In a multivariate analysis including all variables, age lost its significance. In both sexes there were independent positive relations between intact PTH and body mass index and 1,25(OH)2D3, and negative relations between PTH and smoking habits as well as 25(OH)D3; among men there was also negative relations between PTH and coffee consumption. The results indicate that life-style factors such as smoking and coffee consumption decrease the serum concentration of intact PTH, and the same effect is seen in individuals with low body mass index. Coffee intake, smoking, and low body mass index are also known to adversely affect bone mineral content, highlighting the relationship between PTH and bone metabolism.

Blood pressure inversely correlates with thrombin-evoked calcium rise in platelets

Earlier investigations showed a positive correlation between basal cytosolic free calcium in human platelets and blood pressure; however, recent studies have failed to show this relation. We undertook the present work to examine which platelet cytosolic calcium parameters (namely, cytosolic calcium in resting or stimulated states in calcium-containing and calcium-free media) present the least variability and best correlation with blood pressure. We studied 17 healthy white men on three different occasions separated by 1- and 4-week intervals. Their manual and ambulatory automated 24-hour blood pressure measurements were correlated with cytosolic calcium in resting and stimulated (thrombin-treated) fura 2-loaded platelets. The following cytosolic calcium parameters were measured in 1 mmol/L calcium and calcium-free media: basal cytosolic calcium, peak thrombin-evoked cytosolic calcium, and post-transient cytosolic calcium 5 minutes after thrombin treatment. The highest and lowest coefficients of variation were respectively shown by the basal cytosolic calcium (22.8%) and peak thrombin-evoked cytosolic calcium (10.1%) in calcium medium. Basal cytosolic calcium did not correlate with any of the blood pressure parameters. Of the cytosolic calcium parameters, peak thrombin-evoked cytosolic calcium in calcium medium demonstrated consistent (negative) correlations with blood pressure, with better correlations shown with diastolic than systolic blood pressure of both automated and manual blood pressure readings. Peak thrombin-evoked cytosolic calcium in calcium medium showed similar correlations with nighttime and daytime automated blood pressure measurements. There were no correlations between peak thrombin-evoked cytosolic calcium in calcium-free medium and blood pressure.(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.

Hyperparathyroidism, platelet intracellular free calcium and hypertension in chronic renal failure

To investigate possible relationships between hyperparathyroidism, alterations in intracellular free calcium concentration ([Ca2+]i) and hypertension in chronic renal failure, serum concentrations of intact parathyroid hormone (PTH) were measured by two-site immunometric assay, and platelet ([Ca2+]i) was assessed using the fluorescent indicator fura-2. Thirty-six patients with chronic renal failure were studied, 10 with normal serum PTH concentrations (mean 8.0 +/- 0.6 pmol/liter), 17 with elevated serum PTH (35.0 +/- 7.2 pmol/liter) and 9 patients with elevated PTH (36.2 +/- 5.9 pmol/liter) who were receiving nifedipine. Platelet [Ca2+]i was increased in patients with elevated PTH, compared with those in whom PTH was normal (138 +/- 16 vs. 83 +/- 7 nmol/liter, P < 0.01). A linear relation was observed between serum PTH and platelet [Ca2+]i in these patients (r = 0.818, P < 0.001). In contrast, platelet [Ca2+]i was not elevated (84 +/- 9 nmol/liter) in the patients with elevated PTH who were receiving nifedipine. A linear relation was also present between both serum PTH (r = 0.616, P < 0.001) and platelet [Ca2+]i (r = 0.576, P < 0.005) and mean blood pressure. Nine patients with hyperparathyroidism were restudied after treatment with the vitamin D analogue alfacalcidol. This resulted in significant decreases in serum PTH (P < 0.01), platelet [Ca2+]i (P < 0.02), and mean blood pressure (P < 0.05). These studies indicate that [Ca2+]i may be increased early in renal failure, and that this increase occurs in association with both hyperparathyroidism and hypertension. Furthermore, treatment of hyperparathyroidism with alfacalcidol may result in reductions in both [Ca2+]i and blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet sodium-hydrogen antiport in obese and diabetic black women

In this investigation we correlated platelet Na-H antiport parameters with blood pressure and serum lipids in a sample population of non-insulin-dependent diabetic obese, nondiabetic obese, and nondiabetic nonobese black women. Parameters of the Na-H antiport were examined in aspirin-treated platelets. These parameters were not altered in resting or in thrombin-stimulated platelets of diabetic patients. The activity index of platelet Na-H antiport after thrombin stimulation was positively correlated with the blood pressure (systolic blood pressure, r = 0.5320 and p = 0.0001; diastolic blood pressure, r = 0.5123 and p = 0.0017). Lower high density lipoprotein cholesterol levels were associated with an alkaline shift in the cytosolic pH set point for activation of the Na-H antiport. Highly significant correlations were also observed between the total cholesterol/high density lipoprotein cholesterol ratio and the cytosolic pH set point for activation of the Na-H antiport. These correlations were independent of diabetes or the body mass index. Together, these observations indicate that parameters of platelet Na-H antiport are altered with an increase in blood pressure and a decrease in serum high density lipoprotein cholesterol.