Association of calcitriol and blood pressure in normotensive men

PHOSPHORUS METABOLISM AND MANAGEMENT IN CHRONIC KIDNEY DISEASE: Phosphate Metabolism in the Setting of Chronic Kidney Disease: Significance and Recommendations for Treatment

Phosphorus is an essential mineral that plays a crucial role in cell structure and metabolism. In living organisms, phosphorus exists surrounded by four oxygen atoms to form phosphate (PO(4)). Within cells, PO(4) regulates enzymatic activity and serves as an essential component of nucleic acids, adenosine triphosphate, and phospholipid membranes. Outside cells, PO(4) primarily resides in bone and teeth as hydroxyapatite. A small amount of inorganic PO(4) circulates in serum, with levels balanced by gastrointestinal intake, renal excretion, and a set of specific hormones. Under normal conditions, PO(4) is excreted through the kidneys. Among patients with end stage renal disease (ESRD) receiving chronic dialysis, circulating PO(4) levels typically rise to levels well above the normal laboratory range. Higher serum PO(4) levels are strongly associated with arterial calcification and mortality in this setting. Among predialysis patients with chronic kidney disease (CKD), phosphaturic hormones enhance renal PO(4) excretion to maintain serum PO(4) levels within the high-normal laboratory range. Recently, high-normal serum PO(4) levels have been associated with cardiovascular (CV) events and mortality among individuals who have CKD and among those who have normal kidney function. This review discusses PO(4) metabolism in the context of CKD, examines associations of PO(4) levels with adverse outcomes in the CKD setting, and suggests treatment strategies for moderating serum PO(4) levels.

Vitamin D status and parathyroid hormone levels in relation to blood pressure: a population-based study in older men and women

BACKGROUND

Evidence is accumulating that the vitamin D endocrine system has physiological functions beyond bone health including a role in the regulation of blood pressure. Effects of poor vitamin D status on blood pressure may be mediated by elevated parathyroid hormone (PTH) levels.

AIM

To evaluate whether serum 25-hydroxyvitamin D [25(OH)D] and PTH levels are independently associated with blood pressure in a population-based study of older men and women.

METHODS

Subjects were participants of the Longitudinal Aging Study Amsterdam, aged 65 years and older. In 1205 participants, serum 25(OH)D and PTH levels were determined and diastolic and systolic blood pressure were measured. Linear and logistic regression analyses were performed with adjustments for age, sex, region, season, lifestyle factors (physical activity, smoking, alcohol intake), and waist circumference.

RESULTS

Serum 25(OH)D was not significantly associated with diastolic (beta 0.00, P = 0.98) or systolic (beta 0.06, P = 0.11) blood pressure. In contrast, higher ln-PTH levels were significantly associated with higher diastolic (beta 1.93, P = 0.03) and systolic (beta 4.67, P = 0.01) blood pressure. Higher PTH levels were associated with a substantially higher prevalence of hypertension (OR 2.00, 95% CI 1.31-3.06 for the highest versus the lowest quartile), whereas 25(OH)D showed no significant association (OR 0.89, 95% CI 0.47-1.69 for the lowest versus the highest 25(OH)D category).

CONCLUSION

These results indicate that PTH is a potentially modifiable determinant of blood pressure in the general elderly population. Serum 25(OH)D, however, was not associated with blood pressure, possibly due to the relatively high levels in our population.

The Relationship of Target Organ Damage and 24-Hour Ambulatory Blood Pressure Monitoring with Vitamin D Receptor Gene Fok-I Polymorphism in Essential Hypertension

BACKGROUND

The contribution of genetic factors in hypertension cannot be denied.

METHODS

In this study we evaluated the relationship between vitamin D receptor (VDR) gene polymorphisms (Bsm-I, Apa-I and Fok-I), and target organ damage in 74 patients (female/male 49/25, mean age 49.2 +/- 8 years) with essential hypertension. The VDR genotypes were evaluated by polymerase chain reaction and digestion of the amplified products by related enzymes. Patients with diabetes mellitus or impaired glucose tolerance and severe obesity were excluded. All patients underwent a complete physical examination, full biochemistry and urinalysis; in addition, all of them were assessed for target organ damage. Twenty-four-hour ambulatory blood pressure monitoring was performed in all patients.

RESULTS

No significant difference was detected in biochemistry results and physical examination between groups for Bsm-I and Apa-I VDR gene polymorphisms. Patients were distributed as FF (n = 39) and non-FF (Ff/ff, n = 35) for Fok-I polymorphism. A negative correlation was present between vitamin D levels and day-time interval and early morning average by the measurement of 24-hour ambulatory blood pressure in the non-FF group. Serum cystatin-C was higher in the non-FF group (p = 0.012). In addition on retinal examination, the degree and presence of retinopathy were significantly higher in the non-FF group when compared to the FF group (p = 0.025, p = 0.018, respectively).

CONCLUSION

Knowing the VDR gene polymorphisms status may be helpful in preventing target organ damage in hypertensive patients.

Mineral metabolism and arterial functions in end-stage renal disease: potential role of 25-hydroxyvitamin D deficiency

In ESRD, arterial function is abnormal, characterized by decreased capacitive function (arterial stiffening) and reduced conduit function, shown by diminished flow-mediated dilation (FMD). The pathophysiology of these abnormalities is not clear, and this cross-sectional study analyzed possible relationships among arterial alterations and cardiovascular risk factors, including mineral metabolism parameters, such as serum parathormone, and vitamin D "nutritional" and "hormonal" status by measuring serum 25-hydroxyvitamin D [25(OH)D(3)] and 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] levels. Aortic stiffness (pulse wave velocity), brachial artery (BA) distensibility (echotracking; n = 42), BA FMD (hand-warming; n = 37), and arterial calcification scores (echography and plain x-rays) were measured in 52 stable and uncomplicated patients who were on hemodialysis. 25(OH)D(3) and 1,25(OH)(2)D(3) serum levels were low and weakly correlated (r = 0.365, P < 0.05). After adjustment for BP and age, multivariate analyses indicated that 25(OH)D(3) and 1,25(OH)(2)D(3) were negatively correlated with aortic pulse wave velocity (P < 0.001) and positively correlated with BA distensibility (P < 0.01) and FMD (P < 0.001). Arterial calcification scores were not independently associated with 25(OH)D(3) and 1,25(OH)(2)D(3) serum concentrations. These results suggest that nutritional vitamin D deficiency and low 1,25(OH)(2)D(3) could be associated with arteriosclerosis and endothelial dysfunction in patients who have ESRD and are on hemodialysis.

Effects of ACE gene polymorphism on vitamin D therapy according to parathyroid hormone level in patients on hemodialysis

Medical management is still far from optimal in secondary hyperparathyroidism. This may be explained, at least in part, by genetic differences. The aim of this study was to evaluate the association of genetic influences of angiotensinconverting enzyme (ACE) gene polymorphisms with response to vitamin D therapy among patients on hemodialysis (HD). Eighty-two patients (female/male, 34/48; mean age, 47.5+/-15.3 y; HD duration time, 76.6+/-33.2 mo) with endstage renal disease who were on maintenance HD were included in the study. Five-year retrospective demographic, clinical, laboratory, and treatment data (5-y cumulative doses of phosphate-binding drugs and oral and intravenous cumulative doses of active vitamin D) were retrieved from patients' hospital records. ACE gene polymorphisms of patients were documented and were used to group patients as follows: The insertion/deletion polymorphism group (I/D) consisted of (1) group non-DD (n=43), who had the DI or II allele, and (2) group DD (n=39), who had the DD allele. Patients with the DD allele (group DD) of ACE gene polymorphism had (1) significantly elevated mean 5-y intact parathyroid hormone levels when compared with the non-DD group (P=.009), and (2) significantly elevated oral and intravenous 5-y cumulative doses of vitamin D. Oral and intravenous 5-y cumulative doses of vitamin D used in group DD patients were significantly higher than those in group I patients (P=.038 and P=.037, respectively). Knowledge of genetic differences among patients on HD may be useful to the clinician in planning treatment strategy. ACE gene polymorphism may have an effect on hyperparathyroidism, as is seen in patients on HD. Patients from this group who have resistant hyperparathyroidism may be candidates for ACE inhibitor therapy.

Analogs of 1α,25-dihydroxyvitamin D3 with high potency in induction of osteoclastogenesis and prevention of dendritic cell differentiation: Synthesis and biological evaluation of 2-substituted 19-norvitamin D analogs

In our previous papers, we found that introduction of a substituent at C(2) into 1alpha,25-dihydroxy-19-norvitamin D(3) (2a) caused dramatic changes in binding affinity for the vitamin D receptor (VDR) and in transcriptional activity compared with the parent compound. To investigate the broad biological activity of 2-substituted 19-norvitamin D analogs, we synthesized two new (20S)-2-hydroxyethylidene-19-norvitamin D derivatives (3b and 4b) and a total of 16 A-ring-modified analogs including 3b and 4b were tested for the following in vitro and in vivo biological activities: (1) affinity for the VDR, (2) transcriptional activity, (3) osteoclast formation, (4) bone calcium mobilization in rats, and (5) effects on differentiation of dendritic cells (DCs). The biological effects of the analogs were compared with those of 1alpha,25-dihydroxyvitamin D(3) (1a) and 2MD, which is being developed for the treatment of osteoporosis. The efficacy of the (20S)-19-norvitamin D analogs with 2-hydroxyethylidene, 2-hydroxyethoxy, and 2-methyl moieties (3b, 5b, 6b, and 9b) was more than 10-fold stronger than that of 1a with respect to transcriptional activity, ability to induce osteoclast formation, and ability to inhibit CD86 expression, a marker of mature DCs, and was similar to that of 2MD. The (20S)-2beta-hydroxyethoxy derivative 6b was 2 orders of magnitude more active than 1a and approximately twice as potent as 2MD in preventing CD86 production. The 2-epoxy derivatives 7 and 8 were relatively poor ligands for the VDR and exhibited activity lower than that of the natural hormone 1a.

Association of prevalent hypertension with 24-hour urinary excretion of calcium, citrate, and other factors

BACKGROUND

The relation between hypertension and the urinary excretion of calcium, citrate, and other factors is unclear. It has been proposed that increased urinary calcium excretion is a central feature of essential hypertension. Metabolic acidosis also may be associated with hypertension and decreases urinary citrate levels.

METHODS

To compare the urine composition of individuals with and without hypertension, we studied 24-hour urinary excretion of calcium, citrate, oxalate, uric acid, sodium, magnesium, potassium, phosphorus, and creatinine and pH in a subset of participants with and without nephrolithiasis in the Nurses' Health Study I (older women; N = 1,284), Nurses' Health Study II (younger women; N = 952), and the Health Professionals Follow-up Study (men; N = 788). Logistic regression models adjusted for age, weight, dietary intake, and urinary factors.

RESULTS

In participants with and without nephrolithiasis, citrate was the only urinary factor consistently related to hypertension. Compared with those in the lowest quartile of urinary citrate excretion, multivariate odds ratios of prevalent hypertension in the highest quartile were 0.37 (95% confidence interval [CI], 0.24 to 0.55; P trend < 0.001) for older women, 0.54 (95% CI, 0.32 to 0.92; P trend = 0.03) for younger women, and 0.27 (95% CI, 0.16 to 0.45; P trend < 0.001) for men. Urinary calcium levels were not related consistently to hypertension. Excluding participants with single 24-hour urine collections and those administered thiazide diuretics or angiotensin-converting enzyme inhibitors did not change the results.

CONCLUSION

Lower urinary citrate excretion is associated independently with prevalent hypertension. Factors that regulate urinary citrate excretion may play a role in hypertension.

Vitamin D and its analogues: do they protect against cardiovascular disease in patients with kidney disease?

BACKGROUND

Patients with chronic kidney disease (CKD) are at high risk for cardiovascular disease, and despite recent advances in hypertension control, anemia management, and dialysis adequacy, mortality remains high. Improved understanding of nontraditional risk factors, including those present at early phases in CKD, may lead to novel therapeutic strategies. CKD has been demonstrated to be an independent risk factor for cardiovascular disease in the general population, but data are lacking as to the associated potential abnormalities that occur in association with reduced glomerular filtration rate (GFR), which may contribute to this increased risk. Data are accumulating regarding the role of abnormalities of calcium, phosphorus, vitamin D, and parathyroid hormone (PTH) in cardiovascular disease. Vitamin D deficiency is present even in the early stages of CKD. Vitamin D plays a central role in calcium-phosphorus homeostasis, regulation of PTH, and formation and maintenance of bone. However, until recently, vitamin D has not been considered to have a biologic role in CKD beyond mineral regulation, or has been considered as a negative factor contributing to soft tissue and cardiovascular calcification. In light of recent observational studies showing an association of vitamin D therapy and survival benefit in hemodialysis patients, the effects of vitamin D on cardiovascular system have become a heavily debated issue.

METHODS

A Medline search was performed to identify relevant literature describing the role of vitamin D in the pathogenesis of cardiovascular disease. Both the experimental and clinical literatures in English were reviewed.

RESULTS

The accumulating published data demonstrate both associative relationships and mechanisms for biologic plausibility. The following three potential mechanisms may be important for the protective effects of vitamin D against cardiovascular disease mortality: vitamin D can inhibit various aspects of inflammation, which have been established as a key pathogenic mechanism in atherosclerosis; vitamin D exerts an antiproliferative effect on myocardial cell hypertrophy and proliferation, which underlies the pathogenesis of congestive heart failure; and vitamin D acts as a negative endocrine regulator for the renin-angiotensin system, which itself plays an important independent role in hypertension and cardiovascular health.

CONCLUSION

Vitamin D deficiency might be an underestimated nonclassical risk factor for cardiovascular disease in CKD. Based on a review of the evidence, from both basic science and clinical studies, this article supports the possible protective role of vitamin D beyond its effect on mineral metabolism, and suggests the need for ongoing evaluation of the role of vitamin D in cardiovascular health in the CKD population.

The role of vitamin D in left ventricular hypertrophy and cardiac function

The role of vitamin D in left ventricular hypertrophy and cardiac function. Cardiovascular disease is the leading cause of death among patients with end-stage renal disease (ESRD). Traditional cardiac risk factors, as well as other factors specific to the ESRD population such as hyperphosphatemia, elevated calcium and phosphate product, abnormal lipid metabolism, hyperhomocysteinemia, and chronic inflammation play a role in the excessive risk of cardiovascular death in this population. Left ventricular disorders are proven risk factors for cardiac mortality in hemodialysis patients. These disorders are present in incident ESRD patients at rates far above the general population. There is an accumulating body of evidence that suggests that vitamin D plays a role in cardiovascular disease. Abnormal vitamin metabolism, through deficiency of the active form of 1,25-dihydroxyvitamin D(3), and acquired vitamin D resistance through the uremic state, have been shown to be important in ESRD. Vitamin D deficiency has long been known to affect cardiac contractility, vascular tone, cardiac collagen content, and cardiac tissue maturation. Recent studies using vitamin D receptor deficient mice as a model demonstrate a crucial role of vitamin D in regulation of the renin-angiotensin system. Additionally, there is emerging evidence linking treatment with vitamin D to improved survival on hemodialysis and improvement in cardiac function. The emergence of this data is focusing attention on the previously underappreciated nonmineral homeostatic effects of vitamin D that very likely play an important role in the pathogenesis of cardiac disease in ESRD.

VITAMIN D IN HEALTH AND DISEASE: Beyond Minerals and Parathyroid Hormone: Role of Active Vitamin D in End-Stage Renal Disease

Secondary hyperparathyroidism is a common complication of end-stage renal disease (ESRD) that is often treated with activated forms of intravenous vitamin D. The natural course and treatment of secondary hyperparathyroidism in hemodialysis patients is punctuated by episodes of hypercalcemia, hyperphosphatemia, and increased calcium-phosphate product, which in previous studies were linked to increased mortality. Historically these episodes have been attributed to vitamin D, leading some authorities to favor decreased vitamin D use. However, the studies that examined the impact of mineral levels and parathyroid hormone (PTH) on survival did not consistently account for vitamin D therapy itself on hemodialysis patient survival. The current review examines in detail two recent large-scale studies of hemodialysis patients: one that demonstrated a survival advantage of paricalcitol over calcitriol and a second that demonstrated a significant survival advantage of any intravenous vitamin D formulation versus none. In both studies, the effects were independent of mineral and PTH levels, suggesting "nontraditional" actions of vitamin D contributed to the observed survival advantage. Several of these nontraditional actions are reviewed with an emphasis on those that might impact hemodialysis outcomes.

Activated injectable vitamin D and hemodialysis survival: a historical cohort study

Patients with ESRD commonly experience secondary hyperparathyroidism, a condition primarily managed with activated injectable vitamin D. The biologic effects of vitamin D, however, are widespread, and it is possible that activated injectable vitamin D alters survival in ESRD. This hypothesis was tested in a historical cohort study of incident hemodialysis patients who lived throughout the United States between January 1996 and December 1999. The primary outcome was 2-yr survival among those who survived for at least 90 d after initiation of chronic hemodialysis. During this period, 51,037 chronic hemodialysis patients survived for at least 90 d from the initiation of hemodialysis, and in the ensuing 2 yr, 37,173 received activated injectable vitamin D and 13,864 did not. At 2 yr, mortality rates were 13.8/100 person-years in the group that received injectable vitamin D compared with 28.6/100 person-years in the group that did not (P < 0.001). Cox proportional hazards analyses adjusting for several potential confounders and examining injectable vitamin D therapy as a time-dependent exposure suggested that compared with patients who did not receive injectable vitamin D, the 2-yr survival advantage associated with the group that did receive injectable vitamin D was 20% (hazard ratio, 0.80; 95% confidence interval, 0.76 to 0.83). The incidence of cardiovascular-related mortality was 7.6/100 person-years in the injectable vitamin D group, compared with 14.6/100 person-years in the non-vitamin D group (P < 0.001). The benefit of injectable vitamin D was evident in 48 of 49 strata examined, including those with low serum levels of intact parathyroid hormone and elevated levels of serum calcium and phosphorus, situations in which injectable vitamin D is often withheld. Repeating the entire analysis using marginal structural models to adjust for time-dependent confounding by indication yielded a survival advantage of 26% (hazard ratio, 0.74; 95% confidence interval, 0.71 to 0.79) associated with the injectable vitamin D group. In this historical cohort study, chronic hemodialysis patients in the group that received injectable vitamin D had a significant survival advantage over patients who did not. Randomized clinical trials would permit definitive conclusions.

Vitamin D: a negative endocrine regulator of the renin-angiotensin system and blood pressure

The renin-angiotensin system (RAS) plays a central role in the regulation of blood pressure, volume and electrolyte homeostasis. Inappropriate activation of the RAS may lead to hypertension. Clinical and epidemiological studies have suggested a correlation between Vitamin D-deficiency and high blood pressure. Our recent studies demonstrate that Vitamin D is a potent endocrine suppressor of renin biosynthesis to regulate the RAS. Mice lacking the Vitamin D receptor (VDR) have elevated production of renin and angiotensin (Ang) II, leading to hypertension, cardiac hypertrophy and increased water intake. These abnormalities can be prevented by treatment with an ACE inhibitor or AT(1) receptor antagonist. Vitamin D repression of renin expression is independent of calcium metabolism, the volume- and salt-sensing mechanisms and the Ang II feedback regulation. In normal mice, Vitamin D-deficiency stimulates renin expression, whereas injection of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] reduces renin synthesis. In cell cultures, 1,25(OH)(2)D(3) directly suppresses renin gene transcription by a VDR-dependent mechanism. Furthermore, we have found that Gemini compounds have more potent renin-suppressing activity than 1,25(OH)(2)D(3). Collectively, our studies reveal a critical role of the Vitamin D endocrine system in the regulation of blood pressure and volume homeostasis, and suggest that low calcemic Vitamin D analogs may potentially be developed into a new class of anti-hypertensive agents to control renin production and blood pressure.

Effect of ANG II type I receptor antagonist and ACE inhibitor on vitamin D receptor-null mice

We recently showed that vitamin D receptor (VDR) inactivation results in deregulated stimulation of the renin-angiotensin system (RAS). To address further the relation between RAS activation and the abnormalities in electrolyte and volume homeostasis, we studied the effect of the ANG II type I receptor antagonist losartan and the angiotensin-converting enzyme inhibitor captopril on VDR-null mice. Treatment with losartan or captopril normalized the water intake and urine excretion of VDR-null mice. However, the increase in salt excretion in VDR-null mice was not affected by either drug, suggesting that this abnormality is independent of the RAS. Northern blot and immunohistochemical analyses revealed that both drugs caused a drastic stimulation of renin expression in wild-type and VDR-null mice, but renin expression remained much higher in the treated VDR-null mice than in the treated wild-type mice, suggesting that the ANG II feedback mechanism remains intact in the mutant mice. These data firmly established a causative relation between RAS overstimulation and the abnormal volume homeostasis in VDR-null mice and demonstrated that vitamin D repression of renin expression is independent of the ANG II feedback regulation in vivo.

Vitamin D regulation of the renin-angiotensin system

The renin-angiotensin system (RAS) plays a central role in the regulation of blood pressure, electrolyte, and volume homeostasis. Epidemiological and clinical studies have long suggested an association of inadequate sunlight exposure or low serum 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] levels with high blood pressure and/or high plasma renin activity, but the mechanism is not understood. Our recent discovery that 1,25(OH)(2)D(3) functions as a potent negative endocrine regulator of renin gene expression provides some insights into the mechanism. The concept of vitamin D regulation of blood pressure through the RAS opens a new avenue to our understanding of the physiological functions of the vitamin D endocrine system, and provides a basis for exploring the potential use of vitamin D analogues in prevention and treatment of hypertension.

1,25-Dihydroxyvitamin D(3) is a negative endocrine regulator of the renin-angiotensin system

Inappropriate activation of the renin-angiotensin system, which plays a central role in the regulation of blood pressure, electrolyte, and volume homeostasis, may represent a major risk factor for hypertension, heart attack, and stroke. Mounting evidence from clinical studies has demonstrated an inverse relationship between circulating vitamin D levels and the blood pressure and/or plasma renin activity, but the mechanism is not understood. We show here that renin expression and plasma angiotensin II production were increased severalfold in vitamin D receptor-null (VDR-null) mice, leading to hypertension, cardiac hypertrophy, and increased water intake. However, the salt- and volume-sensing mechanisms that control renin synthesis are still intact in the mutant mice. In wild-type mice, inhibition of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] synthesis also led to an increase in renin expression, whereas 1,25(OH)(2)D(3) injection led to renin suppression. We found that vitamin D regulation of renin expression was independent of calcium metabolism and that 1,25(OH)(2)D(3) markedly suppressed renin transcription by a VDR-mediated mechanism in cell cultures. Hence, 1,25(OH)(2)D(3) is a novel negative endocrine regulator of the renin-angiotensin system. Its apparent critical role in electrolytes, volume, and blood pressure homeostasis suggests that vitamin D analogues could help prevent or ameliorate hypertension.

1,25-Dihydroxyvitamin D(3) is a negative endocrine regulator of the renin-angiotensin system

Inappropriate activation of the renin-angiotensin system, which plays a central role in the regulation of blood pressure, electrolyte, and volume homeostasis, may represent a major risk factor for hypertension, heart attack, and stroke. Mounting evidence from clinical studies has demonstrated an inverse relationship between circulating vitamin D levels and the blood pressure and/or plasma renin activity, but the mechanism is not understood. We show here that renin expression and plasma angiotensin II production were increased severalfold in vitamin D receptor-null (VDR-null) mice, leading to hypertension, cardiac hypertrophy, and increased water intake. However, the salt- and volume-sensing mechanisms that control renin synthesis are still intact in the mutant mice. In wild-type mice, inhibition of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] synthesis also led to an increase in renin expression, whereas 1,25(OH)(2)D(3) injection led to renin suppression. We found that vitamin D regulation of renin expression was independent of calcium metabolism and that 1,25(OH)(2)D(3) markedly suppressed renin transcription by a VDR-mediated mechanism in cell cultures. Hence, 1,25(OH)(2)D(3) is a novel negative endocrine regulator of the renin-angiotensin system. Its apparent critical role in electrolytes, volume, and blood pressure homeostasis suggests that vitamin D analogues could help prevent or ameliorate hypertension.

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.

Natural bioactive substances in milk and colostrum: effects on the arterial blood pressure system

High blood pressure is a significant public health problem worldwide which is associated with increased risk of cardiovascular disease, stroke, and renal disease. The development of this disease is influenced by genetic and environmental factors. The results of many studies have linked increased consumption of milk and milk products with lower blood pressure and reduced risk of hypertension. The intake of several minerals found in milk has been demonstrated to have an inverse relationship with blood pressure. Peptides formed during the digestion of milk proteins have also been demonstrated to have a blood pressure lowering effect. Other components in milk that have been examined for their effects on blood pressure have been less promising. More recent data indicate that a dietary pattern that is low in fat, with fruits, vegetables, and low fat dairy products can significantly reduce blood pressure and lower risk of developing high blood pressure.

Parathyroid hormone, vitamin D, and cardiovascular disease in chronic renal failure

BACKGROUND

Parathyroid hormone and vitamin D have been shown to influence cardiac and vascular growth and function experimentally in human subjects with normal renal function. Because of the increased prevalence of hyperparathyroidism and altered vitamin D status in chronic renal failure, these alterations have been considered to contribute to the increased prevalence of cardiovascular disease and hypertension seen in this patient population. Methods and Results. In this article, we review experimental and clinical literature on the cardiovascular effects of parathyroid hormone and vitamin D and relate them to the development of cardiac and vascular dysfunction in uremia, such as: cardiomyopathy, myocardial hypertrophy, and fibrosis, as well as to myocardial ischemia; uremic glucose intolerance, dyslipidemia, and atherosclerosis; hypertension; and vascular and cardiac calcifications.

CONCLUSIONS

The hyperparathyroid state and altered vitamin D status found in uremia contribute to the cardiovascular pathology seen clinically in uremia and also to the excess mortality from cardiovascular causes found in this patient group. The therapeutic implications of these observations are also discussed.

Recovery of impaired K+ channels in mesenteric arteries from spontaneously hypertensive rats by prolonged treatment with cholecalciferol

1. The mechanism responsible for blood pressure reduction in spontaneously hypertensive rats (SHR) after prolonged cholecalciferol treatment was studied. Two-week treatment of SHR with 0.125 mg cholecalciferol kg-1 body weight per day orally caused significant reductions of systolic blood pressure and of the resting perfusion pressure of the mesenteric vascular bed at constant flow. 2. In addition, the treated animals presented a normalization of the maximum vasoconstriction response to noradrenaline and a reduction of the maximum effect of the adrenaline concentration-response curves. This latter effect probably was due to recovery of the impaired Ca(2+)-dependent K+ channels coupled to alpha 2-adrenoceptors since it was prevented by apamin. 3. The treatment with cholecalciferol also normalized the smooth muscle cell membrane potential of de-endothelialized mesenteric arteries of SHR and their hyperpolarizing responses to alpha 2-adrenergic agonists, which were depressed in untreated SHR. 4. In mesenteric rings with endothelium, alpha 2-adrenergic agonists caused similar hyperpolarizing responses in the SHR and in normotensive Wistar (NWR) and Wistar Kyoto (WKY). In non cholecalciferol-treated SHR the hyperpolarizing mediator involved in this effect was NO, while in NWR it was the endothelium-derived hyperpolarizing factor (EDHF). After cholecalciferol treatment, the hyperpolarization induced by alpha 2-adrenergic agonists in SHR smooth muscle cells was mediated by EDHF, as in NWR. 5. Our results indicate that the hypotensive effect of cholecalciferol in the SHR is probably due to the normalization of vascular reactivity, by restoring the functioning of apamin- and ATP-sensitive K+ channels located in the vascular smooth muscle cell membrane, which are impaired in the SHR.