Increased dietary micronutrients decrease serum homocysteine concentrations in patients at high risk of cardiovascular disease.

BACKGROUND: Elevated blood homocysteine is a risk factor for cardiovascular disease. A 5-micromol/L increase is associated with an approximately 70% increase in relative risk of cardiovascular disease in adults. For patients with established risk factors, this risk is likely even greater. OBJECTIVE: Effects of increased dietary folate and recommended intakes of vitamins B-12 and B-6 on serum total homocysteine (tHcy) were assessed in individuals at high risk of cardiovascular disease. DESIGN: This trial was conducted at 10 medical research centers in the United States and Canada and included 491 adults with hypertension, dyslipidemia, type 2 diabetes, or a combination thereof. Participants were randomly assigned to follow a prepared meal plan (PMP; n = 244) or a self-selected diet (SSD; n = 247) for 10 wk, which were matched for macronutrient content. The PMP was fortified to provide >/=100% of the recommended dietary allowances for 23 micronutrients, including folate. RESULTS: Mean folate intakes at 10 wk were 601 +/- 143 microgram/d with the PMP and 270 +/- 107 microgram/d with the SSD. With the PMP, serum tHcy concentrations fell from 10.8 +/- 5.8 to 9.3 +/- 4.9 micromol/L (P < 0.0001) between weeks 0 and 10 and the change was associated with increased intakes of folate, vitamin B-12, and vitamin B-6 and with increased serum and red blood cell folate and serum vitamin B-12 concentrations. tHcy concentrations did not change significantly with the SSD. CONCLUSIONS: The PMP resulted in increased intakes and serum concentrations of folate and vitamin B-12. These changes were associated with reduced serum tHcy concentrations in persons at high risk of cardiovascular disease.

Dietary calcium attenuates platelet aggregation and intracellular Ca2+ mobilization in spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) are known to be blood pressure sensitive to dietary calcium. The effects of dietary calcium on platelet aggregation and intracellular Ca2+ mobilization were assessed by turbidimetric methods and fura-2 methods, respectively, in washed platelets of SHR. Ca2+ ATPase activity was examined in aortic membrane fractions. Six weeks of dietary calcium supplementation attenuated the increase of systolic blood pressure (SBP 199 +/- 16 v 170 +/- 9 mm Hg, P < .001) and thrombin-induced platelet aggregation (84.5 +/- 3.7 v 73.7 +/- 7.4%, P < .004) at 9 weeks of age. The ionomycin-induced intracellular calcium ([Ca2+]i) peak in the absence of external Ca2+, which reflects [Ca2+]i storage size, and thrombin-evoked [Ca2+]i release from [Ca2+]i storage were decreased by 2.0% Ca diet (472 +/- 55 v 370 +/- 23 nmol/L, P < .001, 339 +/- 29 v 278 +/- 33 nmol/L, P < .002). In addition, SBP was positively correlated with platelet aggregation (r = 0.703, P = .0088), thrombin-evoked [Ca2+]i (r = 0.739, P = .0044), and ionomycin-induced [Ca2+]i (r = 0.591, P = .0415), respectively. However, there was no significant effect of dietary calcium on Ca2+-ATPase activity in aortic membranes. These results suggest that dietary calcium supplementation had a beneficial effect on platelets of SHR by attenuating [Ca2+]i mobilization from [Ca2+]i storage. The hypotensive effect of dietary calcium might be associated with attenuated [Ca2+]i mobilization in SHR.

Tissue-specific expression of the PAL3 promoter requires the interaction of two conserved cis sequences.

The bean PAL2 and PAL3 promoters confer expression in overlapping sets of tissue types in transgenic tobacco. The PAL3 promoter contains motifs that resemble two AC cis elements which are required for tissue-specific expression of the PAL2 promoter. The functions of these motifs in the PAL3 promoter were determined by analysis of mutated PAL3 promoter-GUS constructs in transgenic tobacco. This revealed that the AC motifs are necessary for tissue-specific expression of the PAL3 promoter. Therefore, a key role is indicated for AC elements, which are Myb-protein binding sites, in regulating tissue-specific expression of the bean PAL gene family.

Mechanisms of calcium's effects on blood pressure.

Manipulations of dietary calcium have been repeatedly shown to alter blood pressure in animal models of human essential hypertension. Supplemental dietary calcium lowers blood pressure, whereas restricted calcium diets tend to elevate blood pressure. The mechanisms responsible have not been identified, but numerous possibilities have been proposed. Many of the proposals have attempted to relate dietary calcium to calcium metabolism in vascular smooth muscle and altered vascular tone. Other proposals have focused on neural, hormonal, and renal effects of dietary calcium. In this article, mechanisms through which elevations in extracellular calcium levels might influence intracellular calcium levels are explored. Also examined are the potential roles of calcium regulating hormones, sympathetic nervous system, and electrolyte interactions in modifying blood pressure.

Dietary calcium, defective cellular Ca2+ handling, and arterial pressure control.

The association between dietary calcium intake, calcium metabolism, and blood pressure form the basis of this review. Epidemiologic data consistently show an inverse relationship between dietary calcium and blood pressure. Clinical trials of calcium supplementation have not been as consistent in outcome. Approximately two-thirds of the supplementation studies have found a beneficial effect of calcium on blood pressure. The lack of consistency in outcome from the clinical trials relative to the epidemiological literature may be related to calcium intake. The epidemiological literature indicates an inverse relationship between calcium intake and blood pressure, with those individuals with the lowest calcium intake (< 700 mg/day) having the highest blood pressure. Clinical studies utilizing patients with high baseline calcium levels (> 700 mg/day) may not see an effect of calcium supplementation on blood pressure because of a ceiling effect. Supplemental calcium appears to correct a defect in calcium handling characterized by a renal calcium leak, increased circulating parathroid hormone, and increased intracellular calcium levels. In part, the deficit in cellular calcium homeostasis may be a consequence of abnormal calmodulin activity. Specifically, it appears that calmodulin activity is diminished in experimental hypertension and that increasing dietary calcium may improve calmodulin activity in the spontaneously hypertensive rat. The deficit in calmodulin activity has the potential to interfere with a number of cellular processes crucial to the regulation of cell function and maintenance of appropriate vascular tone. It is concluded that additional research should be directed toward understanding the ramifications of altered calmodulin activity in hypertension and the influence that dietary calcium can have on the activity of calmodulin.

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.

The interactive effects of dietary sodium chloride and calcium on cardiovascular stress responses.

Blood pressure increases associated with salt loading in the spontaneously hypertensive rat (SHR) are attenuated with increased dietary calcium. To assess the cardiovascular effects of these nutrients during stress, blood pressure and sympathoadrenal responses to stress were compared in salt-sensitive SHRs fed diets containing normal (0.73%) or high (8.0%) NaCl combined with either low (0.2%) or high (2.0%) calcium. NaCl-loaded rats showed increased blood pressure and exaggerated plasma epinephrine changes during restraint stress. Elevated blood pressure responses to exogenous NE were also observed with high salt intake. Supplementary calcium reduced blood pressure and attenuated the hypertensive effect of NaCl during restraint stress. Animals fed the high calcium diets had lower plasma epinephrine levels while vascular reactivity was not affected. The results indicate that increased sympathoadrenal activity and vascular reactivity contribute to elevated blood pressure and exaggerated pressor responses produced by NaCl loading in the salt-sensitive SHR. However, the hypotensive effects of dietary calcium appear to be related to sympathoadrenal activity but not vascular reactivity.

Dietary calcium and iron: effects on blood pressure and hematocrit in young spontaneously hypertensive rats.

Supplemental dietary calcium in spontaneously hypertensive rats (SHRs) aged 21-28 d produces a decrease in blood pressure and hematocrit. The simultaneous fall in hematocrit and blood pressure suggests that the changes in blood pressure may be, in part, a consequence of the decrease in hematocrit and reduction in viscosity. To examine this possibility, SHRs aged 21 d were placed on one of four diets varying in iron content. At age 28, the animals showed iron-induced variations in hematocrit (P less than 0.001) but no difference in blood pressure. Subsequent manipulation of the ratio of calcium and iron in the diets of additional groups of animals resulted in variations in hematocrit that were independent of the calcium-induced alterations in blood pressure. We conclude that the effects of calcium on blood pressure are relatively independent of its effects on hematocrit.

Effects of dietary sodium and calcium on blood pressure reactivity in the SHR and WKY.

Salt-sensitive spontaneously hypertensive rats (SHR) and their normotensive control strain, Wistar-Kyoto rats (WKY) were fed four diets varying in sodium chloride and calcium content in order to assess the effects of diet on learned blood pressure responses. The animals were exposed to a classical conditioning paradigm in which one tone was always followed by a brief electric shock and a second tone was never followed by shock. Sodium chloride loading raised baseline blood pressure in both strains, while supplemental calcium attenuated blood pressure. Sodium chloride potentiated blood pressure orienting responses to initial presentations of the tones among calcium deficient, but not calcium replete SHR. Increased sodium chloride intake also potentiated the learned pressor responses to the tone paired with shock in the SHR, but not the WKY. Calcium intake had no apparent effect on the learned blood pressure responses to the two tones.

Genetic variability in response to dietary calcium.

Supplemental dietary calcium has been shown to reduce blood pressure in spontaneously hypertensive rats while restricted calcium diets cause an elevation in blood pressure. This latter nutrient effect has been enhanced by modest sodium restriction and is associated with a reduction in serum ionized calcium concentration. To determine whether alterations of dietary calcium and sodium have a similar influence on blood pressure in genetically normotensive rats, Fisher 344, Wistar Furth, and ACI rats were fed either a low (0.1%) calcium, low (0.25%) sodium diet or normal (1.0%) calcium, normal sodium (0.45%) diet from 4 weeks of age through 29 weeks of age. Indirect measurements of systolic blood pressure showed that only the Fisher 344 rats consistently responded to the low calcium/low sodium diets with an elevation of blood pressure. There was considerable variation in serum electrolytes across strains in the normal diets but all three strains experienced a reduction in ionized calcium and an elevation in phosphorus and magnesium on the restricted diets. In the Fisher 344 rats there were significant (p less than .05) inverse correlations among systolic blood pressure and serum ionized and total calcium concentrations and positive correlations among systolic blood pressure, phosphorus, and magnesium. There was no significant correlation between serum electrolytes and blood pressure in the other two strains. The data indicate that there is genetic variability in the blood pressure response to alterations in dietary calcium and sodium. The pattern of change in serum electrolytes across strains suggests that diet-induced alterations of serum electrolytes, specifically calcium, are not necessarily predictive of a pressor response. It would appear that some other calcium-sensitive physiological process involved in blood pressure regulation must respond differentially to calcium availability across strains.

Blood pressure development and serum calcium in suckling spontaneously hypertensive rat pups: effects of maternal dietary calcium.

Since perinatal factors and dietary calcium intake have been implicated in the early pathogenesis of hypertension in the spontaneously hypertensive rat (SHR), the effect of maternal dietary calcium intake on blood pressure development in the 3-4-week-old suckling SHR was assessed. Twenty-four 6-week-old female SHR were randomized to either a calcium- (0.1%) and sodium- (0.25%) restricted or calcium- (2.0%) and sodium- (1.0%) supplemented diet. After 19 weeks on the diet they were bred. Immediately following birth, half of the pups were cross-fostered to a dam on the alternative diet and half were fostered to a dam on the same diet as that to which they were exposed in utero. Between the 25th and 28th post-natal day each pup had an intra-arterial catheter placed in a femoral artery. Mean arterial pressure (MAP), serum ionized calcium and total calcium were measured. Pups fostered to dams on restricted-Ca2+ diets had higher MAP (P less than 0.01) and lower serum ionized (P less than 0.01) and total (P less than 0.01) calcium levels. There was a significant inverse correlation between serum ionized Ca2+ and MAP in the pups (r = -0.61, P greater than 0.001). We conclude that maternal dietary calcium intake may be an important perinatal factor in the blood pressure development of the suckling SHR.