Calcium metabolism, renin activity, and the antihypertensive effects of calcium channel blockade

Association of dietary calcium with mortality from all causes, cardiovascular disease and cancer in people with hypertension

Association between calcium intake and premature mortality in the general population has been well studied, but little is known about the association among specific populations. The authors aim to evaluate the association among people with hypertension and to provide a proper reference range of dietary calcium intake. This prospective cohort study included 8534 US adults with hypertension from National Health and Nutrition Examination Survey cycles 2003-2014. Dietary calcium intakes were self-reported and mortality status was ascertained by National Death Index records. During a median follow-up of 5.9 years, 1357 death occurred. Compared with participants of dietary calcium intake in quintile 1, participants in quintiles 2 and 4 had a 27% (HR: 0.73, 95% CI: 0.60-0.89) and a 29% lower risk (HR: 0.71, 95% CI: 0.57-0.88) of all-cause mortality respectively. The authors also observed a 34% lower risk (HR: 0.66, 95% CI: 0.45-0.97) of CVD death among participants in quintile 3 and a 37% lower risk (HR: 0.63, 95% CI: 0.40-0.99) of cancer-related death in participants in quintile 4 respectively. Restricted cubic spline (RCS) regression revealed a consistent protective effect of dietary calcium in participants with a daily intake of over 1000 mg, but a daily intake over 1200 mg fails to show further protective effect. Our findings suggest that elevated dietary calcium was associated with lower mortality risk from all-causes, cardiovascular disease (CVD) and cancer, and supplying sufficient dietary calcium intake, between 1000 and 1200 mg per day, in people with hypertension may be considered cost-effective to decrease risk of premature death.

Risk Factors in Adolescent Hypertension

Hypertension is a complex and multifaceted disease, with many contributing factors. While diet and nutrition are important influences, the confounding effects of overweight and obesity, metabolic and genetic factors, racial and ethnic predispositions, socioeconomic status, cultural influences, growth rate, and pubertal stage have even more influence and make diagnosis quite challenging. The prevalence of hypertension in adolescents far exceeds the numbers who have been diagnosed; studies have found that 75% or more go undiagnosed. This literature review summarizes the challenges of blood pressure classification in adolescents, discusses the impact of these confounding influences, and identifies actions that will improve diagnosis and treatment outcomes.

A review of nutritional factors in hypertension management

Hypertension is a major health problem worldwide. Its attendant morbidity and mortality complications have a great impact on patient's quality of life and survival. Optimizing blood pressure control has been shown to improve overall health outcomes. In addition to pharmacological therapies, nonpharmacological approach such as dietary modification plays an important role in controlling blood pressure. Many dietary components such as sodium, potassium, calcium, and magnesium have been studied substantially in the past decades. While some of these nutrients have clear evidence for their recommendation, some remain controversial and are still of ongoing study. Dietary modification is often discussed with patients and can provide a great benefit in blood pressure regulation. As such, reviewing the current evidence will be very useful in guiding patients and their physician and/or dietician in decision making. In this review article of nutritional factors in hypertension management, we aim to examine the role of nutritional factors individually and as components of whole dietary patterns.

Serum calcium levels and hypertension among U.S. adults

Serum calcium levels have been shown to be associated with cardiovascular disease (CVD); however, it is not clear whether serum calcium levels are related to hypertension, a risk factor for CVD. The authors examined the association between serum calcium and hypertension in a representative sample of US adults. A cross-sectional study of 12,405 third National Health and Nutrition Examination Survey participants 20 years and older was conducted. Serum total and ionized calcium levels were analyzed as quartiles. The main outcome of interest was hypertension (n=3437), defined as self-reported use of antihypertensive medication and/or systolic blood pressure ≥140 mm Hg or diastolic blood pressure ≥90 mm Hg. Elevated serum total calcium levels were positively associated with hypertension, independent of potential confounders including C-reactive protein, estimated glomerular filtration rate, serum albumin, 25(OH)D, and phosphorous. Compared with the lowest quartile of serum total calcium (referent category), the multivariable odds ratio (95% confidence interval) of hypertension was 1.49 (1.15-1.93) for the highest quartile (P=.005). This association persisted in subgroup analyses stratified by sex, age, and race-ethnicity. In contrast, serum ionized calcium levels were not associated with hypertension. Higher serum total calcium levels are positively associated with hypertension in a representative sample of U.S. adults.

Increased sensitivity to diltiazem hypotensive effect in an experimental model of high-renin hypertension

Objectives

The aim of this work was to evaluate the pharmacokinetic–pharmacodynamic properties of diltiazem in an experimental model of high-renin hypertension, such as the aortic coarctated (ACo) rat, to further characterize the responsiveness of this model to calcium channel blockers.

Methods

A ‘shunt’ microdialysis probe was inserted in a carotid artery of anaesthetized ACo and control sham-operated (SO) rats for simultaneous determination of diltiazem plasma concentrations and their effects on mean arterial pressure and heart rate after the intravenous application of 3 and 6 mg/kg of the drug. Correlation between plasma levels and cardiovascular effects was established by fitting the data to a modified Emax model.

Key findings

Volume of distribution was greater in ACo than in SO rats. Diltiazem plasma clearance (Cl) was significantly greater in ACo rats than in normotensive SO rats after administration of diltiazem (6 mg/kg). Moreover, Cl increased with dose in ACo but not in SO rats. No differences were observed in the maximal bradycardic effect comparing both experimental groups, and sensitivity (S0) to diltiazem chronotropic effect was similar comparing SO and ACo rats. Differences were not found in the maximal response of the hypotensive effect comparing SO and ACo rats, but the S0 to diltiazem hypotensive effect was greater in ACo rats than in SO rats.

Conclusions

ACo induced profound changes in diltiazem pharmacokinetic behaviour. In addition, our results suggested an increased sensitivity to diltiazem blood pressure lowering effect in experimental renovascular hypertension with high-renin levels.

Renin-angiotensin system polymorphisms and risk of hypertension: influence of environmental factors

Renin-angiotensin system (RAS) polymorphisms have been studied as candidate risk factors for hypertension with inconsistent results, possibly due to heterogeneity among various environmental factors. We analyzed the association between RAS candidate gene polymorphisms and risk of hypertension among 2722 women and also explored whether these associations varied according to menopausal status, body mass index, and dietary factors. In a main-effects analysis of all 2722 women adjusted for age and race, homozygosity for the AT1R A1166C polymorphism was associated with hypertension (odds ratio, 1.35; 95% confidence interval [CI], 1.03-1.78). We also found that a novel nonsense polymorphism in the aminopeptidase-A gene was associated with hypertension among postmenopausal women (hazard ratio, 1.54; 95% CI, 1.01-2.37), women with inadequate calcium intake (hazard ratio, 2.47; 95% CI, 1.29-4.72) and, marginally, women with inadequate vitamin D intake. In addition, angiotensin-converting enzyme and AT1R A1166C polymorphisms were associated or marginally associated with incident hypertension among postmenopausal women and those with inadequate calcium and vitamin D intakes. These data suggest that demographic and dietary factors may influence the associations between RAS polymorphisms and hypertension and could explain heterogeneity in prior studies.

Treatment of pediatric hypertension

We conducted a MEDLINE search from January 1966-March 1999 to obtain information on clinical trials of treatment of pediatric hypertension. An article was selected for review if it described a randomized or nonrandomized study; randomized studies were given priority. Case reports were considered when studies were unavailable. Review articles were useful in identifying references. According to data we collected, hypertension is present in 1-3% of the pediatric population. Nonpharmacologic treatment may be effective initially in those with mild to moderate disease or as an adjunct to drug therapy. Drugs for treatment of chronic hypertension include calcium channel blockers, angiotensin-converting enzyme inhibitors, diuretics, and beta-blockers. Patient and drug characteristics determine therapy. Intravenous labetalol, nicardipine, and nitroprusside are effective for treating hypertensive emergencies.

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

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

Depressor effect of intraventricular administration of calcium on spontaneously hypertensive rats

The role of central Ca2+ in the regulation of blood pressure (BP) was investigated in conscious spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). Ten microliters of a high Ca2+ solution (Ca2+: 32.6 mM) administered intracerebroventricularly (i.c.v.) decreased the mean arterial pressure (MAP) for more than 20 min in SHR (n = 7, P < 0.005), while no change of MAP was observed in the WKY (n = 6). This depressor response to Ca2+ i.c.v. was dose-dependent at Ca2+ concentrations between 16.3 and 65.2 mM. We also investigated the effect of high Ca2+ i.c.v. in SHR after pretreatment with Ca2+ channel blockers, diltiazem (60 micrograms/10 microliters) or nisoldipine (4, 8, 16 and 32 micrograms/10 microliters), administered i.c.v., the autonomic ganglion blocker, hexamethonium (50 mg/kg), administered i.v. and alpha-methyl-p-tyrosine (100 and 400 micrograms/10 microliters) delivered i.c.v. Pretreatment with i.c.v. diltiazem (n = 8) or nisoldipine (n = 5 for 8 micrograms, n = 6 for 4, 16, 32 micrograms) abolished and/or blunted the decrease of MAP due to high Ca2+. Hexamethonium administered i.v. (n = 6) also canceled the depressor action of i.c.v. Ca2+. Pretreatment with 100 micrograms of i.c.v. alpha-methyl-p-tyrosine could not prevent the depressor action of i.c.v. Ca2+; however, 400 micrograms of alpha-methyl-p-tyrosine administered i.c.v. abolished the effect of i.c.v. Ca2+. Furthermore Ca2+ channel blockers administered i.c.v. in themselves increased MAP in SHR (P < 0.05). These results suggest that central Ca2+ is involved in the central regulation of BP in SHR. This effect may be mediated through changes in sympathetic activity.

Contribution of the central interaction between calcium and sodium to hemodynamic regulation in spontaneously hypertensive rats

The contribution of the central interaction between calcium and sodium to hemodynamic regulation was assessed in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats. The effect of a high calcium solution (Ca2+, 130 mg/dl, 10 microliters) infused into the cerebral ventricle (i.c.v.) on hemodynamic responses induced by a high sodium solution (Na+, 1,000 mEq/1, 10 microliters) i.c.v. and the mechanism by which high Ca2+ affects the hemodynamic responses induced by high Na+ i.c.v. were studied. High Na+ i.c.v. induced a pressor response with tachycardia in the SHRs, but induced a pressor response with reflex bradycardia in the WKYs. Prior treatment with high Ca2+ i.c.v. attenuated the pressor response induced by high Na+ i.c.v. (+55.6 +/- 4.4 to +33.1 +/- 3.2 mmHg, P < 0.01) and restored reflex bradycardia (+86.4 +/- 7.7 to -26.7 +/- 7.6 bpm, P < 0.01) in SHRs. Whereas prior treatment with high Ca2+ i.c.v. attenuated the pressor response (+35.7 +/- 2.0 to +22.2 +/- 4.0 mmHg, P < 0.05), it did not alter the degree of reflex bradycardia (-81.7 +/- 7.1 to -69.2 +/- 120 bpm, n.s.) in WKYs. Ganglionic blockade attenuated the pressor response (+56.9 +/- 3.5 to +42.9 +/- 2.3 mmHg, P < 0.05) and restored reflex bradycardia (+82.1 +/- 10.3 to -65.9 +/- 11.0 bpm, P < 0.01) in SHRs, whereas, inhibition of arginine vasopressin attenuated the pressor response without modification of the tachycardic response.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium antagonists in hypertension

The calcium antagonists are effective and safe agents for the treatment of arterial hypertension. They are well tolerated by the patients. In contrast to other types of antihypertensive agents, they cause few metabolic disturbances. They can be combined with diuretics, beta-blockers, and angiotensin-converting enzyme (ACE) inhibitors. They can be safely prescribed to patients with hypertension and concomitant diseases such as diabetes mellitus, chronic obstructive lung disease, congestive heart failure, gout, renal failure, peripheral atherosclerotic disease, or Raynaud's phenomenon. Dietary sodium restriction during antihypertensive therapy with calcium antagonists is not required for optimal antihypertensive efficacy. The second generation of calcium antagonists especially the dihydropyridine analogues that have greater potency and vascular selectivity, and a longer duration of action, will optimize the treatment of hypertension. Their antiatherosclerotic, antiplatelet, and "antitrophic" effects in experimental models for atherogenesis and hypertension hold great promise for the future since, so far, there has been no major success in reducing the incidence of coronary death by the treatment of hypertension.

Systolic hypertension in the elderly. Relationship with cardiovascular disease

The risk of stroke and myocardial infarction is increased in patients with elevated systolic blood pressure. Although treatment trials have demonstrated the benefit of antihypertensive therapy in elderly patients with diastolic hypertension, the only trial conducted in elderly patients with isolated systolic hypertension is currently in progress. A six-month trial of nonpharmacologic therapy should generally be the initial treatment in patients with isolated systolic hypertension. Then, if systolic pressure remains elevated, a cautious trial of drug treatment is reasonable. The drug used should be started in a low dose, and the dose should be titrated slowly. With this approach, antihypertensive treatment of elderly patients with isolated systolic hypertension may be well tolerated and ultimately beneficial.