Glucose-induced alterations of cytosolic free calcium in cultured rat tail artery vascular smooth muscle cells.

We have previously suggested that hyperglycemia per se may contribute to diabetic hypertensive and vascular disease by altering cellular ion content. To more directly investigate the potential role of glucose in this process, we measured cytosolic free calcium in primary cultures of vascular smooth muscle cells isolated from Sprague-Dawley rat tail artery before and after incubation with 5 (basal), 10, 15, and 20 mM glucose. Glucose significantly elevated cytosolic free calcium in a dose- and time-dependent manner, from 110.0 +/- 5.4 to 124.5 +/- 9.0, 192.7 +/- 20.4, and 228.4 +/- 21.9 nM at 5, 10, 15, and 20 mM glucose concentrations, respectively. This glucose-induced cytosolic free calcium elevation was also specific, no change being observed after incubation with equivalent concentrations of L-glucose or mannitol. This glucose effect was also dependent on extracellular calcium and pH, since these calcium changes were inhibited in an acidotic or a calcium-free medium, or by the competitive calcium antagonist lanthanum. We conclude that ambient glucose concentrations within clinically observed limits may alter cellular calcium ion homeostasis in vascular smooth muscle cells. We suggest that these cellular ionic effects of hyperglycemia may underlie the predisposition to hypertension and vascular diseases among diabetic subjects and/or those with impaired glucose tolerance.

Intracellular ionic consequences of dietary salt loading in essential hypertension. Relation to blood pressure and effects of calcium channel blockade.

To study the ionic basis of salt sensitivity in hypertension, 19F-, 13P-, and 23Na-nuclear magnetic resonance techniques were used to measure cytosolic free calcium (Cai), pH (pHi), free magnesium (Mgi), and sodium (Nai) in erythrocytes of essential hypertensive subjects (n = 19). Individuals were studied for 2 mo each on low- (UNaV < 50 meq/d) and high- (UNaV > 200 meq/d) salt diets, with the concomitant administration of nifedipine (10 mg t.i.d.) or placebo tablets for 1 mo of each diet. Salt loading elevated Cai and Nai while suppressing Mgi and pHi; these changes occurred predominantly in salt-sensitive subjects (n = 9). Nifedipine blunted the pressor response to salt loading > 50% (delta diastolic BP [high-low salt vs placebo] = 5 +/- 2 vs 14 +/- 2 mmHg, P < 0.05) and reversed salt-induced ionic changes, lowering Cai and elevating Mgi and pHi. Regardless of the definition of salt sensitivity, continuous relationships were observed between the pressure response to salt loading, the levels of Cai (r = 0.726, P < 0.001), Nai (r = 0.747, P < 0.001), and pHi (r = -0.754, P < 0.001), and the salt-induced change in Mgi (r = -0.757, P < 0.001). Altogether, these results emphasize the reciprocal and coordinate nature of intracellular ionic changes in response to dietary salt loading and calcium channel blockade in essential hypertension. They suggest that salt sensitivity is mediated by cellular calcium accumulation from the extracellular space, in association with magnesium depletion and acidification. Lastly, interpretation of intracellular ion measurements in the future will require concurrent assessment of dietary salt intake.

Hydrochlorothiazide is not additive to verapamil in treating essential hypertension.

Calcium channel blockers, a newer class of antihypertensive medications, have gained considerable acceptance as monotherapeutic agents, particularly in low renin hypertension where diuretics are also most effective. To study whether thiazide diuretics exert an additional antihypertensive effect in the setting of calcium channel blockade, we gave verapamil hydrochloride (360 mg/d) or hydrochlorothiazide (25 mg/d) alone and in combination in an open study to 13 hypertensive patients with mild to moderate essential hypertension. Both verapamil and hydrochlorothiazide lowered blood pressure (170 +/- 17/109 +/- 6 mm Hg pretreatment to 150 +/- 25/95 +/- 8 mm Hg with verapamil; 170 +/- 5/109 +/- 2 mm Hg pretreatment to 164 +/- 25/103 +/- 10 mm Hg with hydrochlorothiazide), but addition of hydrochlorothiazide to verapamil resulted in no added benefit (150 +/- 25/95 +/- 8 mm Hg vs 150 +/- 20/95 +/- 6 mm Hg). Furthermore, while hydrochlorothiazide lowered serum potassium values (4.2 +/- 0.25 mmol/L to 3.7 +/- 0.35 mmol/L) and stimulated plasma renin activity (1.5 +/- 1.3 ng/mL/h) pretreatment to 3.3 +/- 2.7 ng/mL/h with verapamil), verapamil only modestly elevated renin activity (1.5 +/- 1.3 ng/mL/h pretreatment to 2.7 +/- 2.5 ng/mL/h with verapamil) and did not lower potassium values. Altogether, the data suggest that in essential hypertension, at least for verapamil, concurrent diuretic therapy may not be helpful or warranted.

A randomized trial of improved weight loss with a prepared meal plan in overweight and obese patients: impact on cardiovascular risk reduction.

OBJECTIVE: To assess the long-term effects of a prepackaged, nutritionally complete, prepared meal plan compared with a usual-care diet (UCD) on weight loss and cardiovascular risk factors in overweight and obese persons. DESIGN: In this randomized multicenter study, 302 persons with hypertension and dyslipidemia (n = 183) or with type 2 diabetes mellitus (n = 119) were randomized to the nutrient-fortified prepared meal plan (approximately 22% energy from fat, 58% from carbohydrate, and 20% from protein) or to a macronutrient-equivalent UCD. MAIN OUTCOME MEASURES: The primary outcome measure was weight change. Secondary measures were changes in blood pressure or plasma lipid, lipoprotein, glucose, or glycosylated hemoglobin levels; quality of life; nutrient intake; and dietary compliance. RESULTS: After 1 year, weight change in the hypertension/dyslipidemia group was -5.8+/-6.8 kg with the prepared meal plan vs -1.7+/-6.5 kg with the UCD plan (P<.001); for the type 2 diabetes mellitus group, the change was -3.0+/-5.4 kg with the prepared meal plan vs -1.0+/-3.8 kg with the UCD plan (P<.001) (data given as mean +/- SD). In both groups, both interventions improved blood pressure, total and low-density lipoprotein cholesterol levels, glycosylated hemoglobin level, and quality of life (P<.02); in the diabetic group, the glucose level was reduced (P<.001). Compared with those in the UCD group, participants with hypertension/dyslipidemia in the prepared meal plan group showed greater improvements in total (P<.01) and high-density lipoprotein (P<.03) cholesterol levels, systolic blood pressure (P<.03), and glucose level (P<.03); in participants with type 2 diabetes mellitus, there were greater improvements in glucose (P =.046) and glycosylated hemoglobin (P<.02) levels. The prepared meal plan group also showed greater improvements in quality of life (P<.05) and compliance (P<.001) than the UCD group. CONCLUSIONS: Long-term dietary interventions induced significant weight loss and improved cardiovascular risk in high-risk patients. The prepared meal plan simultaneously provided the simplicity and nutrient composition necessary to maintain long-term compliance and to reduce cardiovascular risk.

Nutritional management of cardiovascular risk factors. A randomized clinical trial.

BACKGROUND: Adherence to dietary recommendations for disease management is often hindered by the complexity of incorporating them into the daily diet. Nutrition and cardiovascular scientists and food technologists collaborated to develop a prepared meal plan that meets national dietary guidelines for cardiovascular risk reduction. OBJECTIVE: To assess the clinical effects of this plan, which incorporates all National Academy of Sciences National Research Council recommended dietary allowances for vitamins, minerals, and macronutrients, compared with a patient-selected American Heart Association Step I and Step II diet plan. METHODS: This multicenter, randomized, parallel-intervention trial was conducted at 10 medical centers in the United States and Canada and involved 560 men and women with hypertension, dyslipidemia, or diabetes. Following calculation of prescriptions to meet individual nutritional requirements based on the Harris-Benedict equation, participants were randomized to the Campbell's Center for Nutrition and Wellness (CCNW) plan, which is composed of prepackaged breakfast, lunch, and dinner meals provided to participants, or a nutritionist-guided American Heart Association Step I and Step II diet, in which participants self-selected foods to meet their nutrition prescription for 10 weeks. MAIN OUTCOME MEASURES: Blood pressure (BP); lipid, glucose, glycosylated hemoglobin (HbA1c), and insulin levels; body weight; dietary intake; and quality of life. RESULTS: Patients' BP, lipid levels, carbohydrate metabolism, weight, and quality of life (P < or = .001 for all findings except low-density lipoprotein-high-density lipoprotein ratio, P = .25) all improved on both nutrition plans. Mean differences (+/-SD) between baseline and treatment clinical values for the CCNW and the self-selected diet groups (between-group P values), respectively, were as follows: systolic BP, -6.4 +/- 9.2 mm Hg and -4.6 +/- 9.0 mm Hg (P = .02); diastolic BP, -4.2 +/- 5.7 mm Hg and -3.0 +/- 5.1 mm Hg (P = .006); cholesterol, -0.32 +/- 0.58 mmol/L and -0.27 +/- 0.56 mmol/L (-12.4 +/- 22.5 mg/dL and -10.4 +/- 21.9 mg/dL) (P = .30); glucose, -0.65 +/- 1.88 mmol/L and -0.75 +/- 2.03 mmol/L (-11.7 +/- 34.0 mg/dL and -13.5 +/- 36.6 mg/dL) (P = .10); and HbA1c, -0.4% +/- 0.8% and -0.3% +/- 0.7% (P = .66). Weight loss with the CCNW and self-selected plans, respectively, was as follows: men, -4.5 +/- 3.6 kg and -3.5 +/- 3.3 kg; and women, -4.8 +/- 3.0 kg and -2.8 +/- 2.8 kg. Quality of life was significantly improved for daily and work activities (P < .05) and nutritional health perceptions (P < .05) with the CCNW plan relative to the self-selected group. Overall nutrient intake and compliance were both significantly (P < .001) better with the CCNW plan. CONCLUSIONS: Nutritionally balanced meals that meet the recommendations of national health organizations improved multiple risk factors for patients with cardiovascular disease. The CCNW plan resulted in greater clinical benefits, nutritional completeness, and compliance than the self-selected diet. The CCNW is a comprehensive nutrition plan, convenient for both prescription and practice, and appears viable for effecting favorable dietary changes in patients at high risk for cardiovascular disease.

Calcium metabolism in hypertension and allied metabolic disorders.

Data suggest a critical role for Ca metabolism in the pathophysiology of hypertensive disease. Intracellularly, all hypertension displays elevated cytosolic free-Ca2+ and suppressed free-Mg2+ levels. Extracellularly, however, heterogeneous defects in Ca and Mg metabolism are observed. This apparent divergence may be explained by considering all hypertension as the expression, in varying degrees, of two underlying Ca-related mechanisms: one (salt sensitive, low renin, Ca(2+)-antagonist sensitive) dependent on inappropriate cellular Ca2+ uptake from the extracellular space and the other (salt insensitive, renin dependent, Ca(2+)-antagonist insensitive) dependent on increased cellular Ca2+ release from intracellular sites. Recent work highlights the role of 1,25-dihydroxyvitamin D3 and the newly described parathyroid hypertensive factor in volume-dependent low-renin forms of hypertension. Altered cellular ion handling may also explain metabolic and clinical correlates of hypertension, e.g., peripheral insulin resistance, hyperinsulinemia, obesity, and non-insulin-dependent diabetes mellitus (NIDDM). Thus, all subjects with NIDDM, whether hypertensive or not, display the same elevated cytosolic free-Ca2+ and suppressed free-Mg2+ levels observed in hypertension. Furthermore, adiposity, the level of blood pressure, and fasting and postglucose hyperinsulinemia are all closely and quantitatively related to intracellular free-Ca2+, free-Mg2+, and pH levels. This suggests a broader hypothesis, in which hypertension, obesity, insulin resistance, and NIDDM, each usually considered a distinct clinical entity, represent different clinical expressions of a common defect in cellular ion handling, hence explaining their frequent clinical coexistence in the general population.

Cellular ions in NIDDM: relation of calcium to hyperglycemia and cardiac mass.

OBJECTIVE: To investigate the role of hyperglycemia in mediating the clinical association of NIDDM with hypertension and left ventricular dysfunction and hypertrophy. RESEARCH DESIGN AND METHODS: Since hyperglycemia elevates cytosolic free calcium (Cai) both in myocardial and vascular smooth muscle cells, we utilized nuclear magnetic resonance (NMR) spectroscopy to measure erythrocyte Cai levels and compared them with serum ionized calcium (Caio), glucose, and insulin values before and following an oral glucose tolerance test (OGTT) and with previously obtained cardiac structural indexes in normotensive and hypertensive NIDDM (n = 32) and normal control subjects (n = 35). RESULTS: Compared with control subjects, normotensive NIDDM subjects had higher Cai (31.5 +/- 2.3 vs. 24.3 +/- 1.9 nmol/l, P = 0.05), lower intracellular free magnesium (Mgi) (200 +/- 10 vs. 225 +/- 7 mumol/l, P = 0.05), and greater posterior wall thickness (0.98 +/- 0.04 vs. 0.86 +/- 0.03 cm, P = 0.05). Hypertensive NIDDM subjects exhibited a further increase in Cai (43.1 +/- 4.4 nmol/l, P = 0.05 vs. control subjects) and left ventricular mass (LVM) (201.5 +/- 12.2 vs. 155.8 +/- 7.7 g, P = 0.05 vs. control subjects). For all subjects, significant relationships were observed between Cai and fasting blood glucose (r = 0.510, P < 0.01), HbAic (r = 0.389, P < 0.05), and the glycemic response to OGTT (the area under the curve [AUC] for glucose; r = 0.519, P < 0.01) and to systolic (r = 0.504, P < 0.01) and diastolic (r = 0.624, P < 0.01) blood pressure. Left ventricular mass index (LVMI) was related to fasting glucose levels (r = 0.406, P < 0.01) and the AUC for glucose (r = 0.380, P < 0.01), but not to fasting insulin or insulin responses to an OGTT. The LVMI was best related to Cai (r = 0.516, P < 0.01), while being inversely related to Caio (r = -0.486, P < 0.01). Multivariate regression indicated the contribution of glucose to LVMI was independent of age, BMI, insulin, and blood pressure but demonstrated a significant interaction with Cai. CONCLUSIONS: Altogether, these data suggest that glucose-related excess Cai is a fundamental lesion in diabetes that contributes to the elevated blood pressure and cardiac mass in this disease.

Multicenter randomized trial of a comprehensive prepared meal program in type 2 diabetes.

OBJECTIVE: To evaluate the clinical effects of a comprehensive prepackaged meal plan, incorporating the overall dietary guidelines of the American Diabetes Association and other national health organizations, relative to those of a self-selected diet based on exchange lists in free-living individuals with type 2 diabetes. RESEARCH DESIGN AND METHODS: A total of 202 women and men (BMI < or = 42 kg/m2) whose diabetes was treated with diet alone or an oral hypoglycemic agent were enrolled at 10 medical centers. After a 4-week baseline period, participants were randomized to a nutrient-fortified prepared meal plan or a self-selected exchange-list diet for 10 weeks. On a caloric basis, both interventions were designed to provide 55-60% carbohydrate, 20-30% fat, and 15-20% protein. At intervals, 3-day food records were completed, and body weight, glycemic control, plasma lipids, and blood pressure were assessed. RESULTS: Food records showed that multiple nutritional improvements were achieved with both diet plans. There were significant overall reductions in body weight and BMI, fasting plasma glucose and serum insulin, fructosamine, HbA1c, total and LDL cholesterol, and blood pressure (P < 0.001 or better for all). In general, differences in major end points between the diet plans were not statistically significant. CONCLUSIONS: Glycemic control and cardiovascular risk factors improve in individuals with type 2 diabetes who consume diets in accordance with the American Diabetes Association guidelines. The prepared meal program was as clinically effective as the exchange-list diet. The prepared meal plan has the additional advantages of being easily prescribed and eliminating the complexities of meeting the multiple dietary recommendations for type 2 diabetes management.

Protective effects of captopril against ischemic stress: role of cellular Mg.

Magnesium (Mg) deficiency enhances tissue sensitivity to ischemic damage, an effect reversed not only by Mg, but also by sulfhydryl (SH)-containing compounds. We therefore created an in vitro model of red blood cell ischemia to investigate whether the protective effects of these compounds might be related to effects on intracellular free Mg (Mg(i)) content. (31)P-nuclear magnetic resonance (NMR) spectroscopy was used to measure the high-energy metabolites ATP and 2,3-diphosphoglycerate (DPG) and Mg(i) and inorganic phosphate (P(i)) levels in erythrocytes before and for 6 hours after progressive oxygen depletion in the presence or absence of SH-compounds, including captopril, N-acetyl-L-cysteine (NAC), penicillamine, and N-(2-mercaptopropionyl)-glycine (MPG). Under basal aerobic conditions, captopril increased Mg(i) in a dose- and time-dependent fashion (174.5+/-5.3 to 217.1+/-5.1 micromol/L, P<0. 05 at 100 micromol/L, 60 minutes). The SH compounds NAC, penicillamine, and MPG but not the non-SH compound enalaprilat also significantly raised Mg(i) in erythrocytes (P<0.05). With oxygen deprivation, a consistent decrease occurred in both ATP and 2,3-DPG levels associated with a rise in P(i) and in the P(i)/2,3-DPG ratio used as an index of high-energy metabolite depletion. Captopril, compared with control, retarded the rise in P(i) and reduced the P(i)/2,3-DPG ratio (P<0.008 and P<0.025 at 4 and 6 hours, respectively). Furthermore, the higher the initial Mg(i) and the greater the captopril-induced rise in Mg(i), the greater the metabolite-protective effect (r=0.799 and r=0.823, respectively; P<0. 01 for both). Altogether, the data suggest that Mg influences the cellular response to ischemia and that the ability of SH compounds such as captopril to ameliorate ischemic injury may at least in part be attributable to the ability of such compounds to increase cytosolic free Mg levels.

Calcium, the renin-aldosterone system, and the hypotensive response to nifedipine.

Ionic, hormonal, and blood pressure responses to a single oral dose of the calcium channel blocker nifedipine were assessed in 25 essential hypertensive subjects. When grouped according to their renin-sodium profile, low renin subjects had a greater hypotensive response to nifedipine (change in diastolic blood pressure -20.0 +/- 1.4 vs -6.4 +/- 1.0%; p less than 0.005) than did high renin hypertensive subjects. The initial level of serum ionized calcium predicted the blood pressure response to nifedipine (r = 0.70, p less than 0.001), as did the initial plasma renin activity (r = 0.65, p less than 0.005). Nifedipine induced a transient rise in serum ionized calcium (from 2.22 +/- 0.02 to 2.28 +/- 0.02 mEq/L; p less than 0.01), while plasma renin activity was consistently elevated compared with initial values at 30 (p less than 0.01), 60 (p less than 0.01), and 120 (p less than 0.05) minutes after drug administration. By comparison, plasma aldosterone levels did not rise and even declined at 30 (p less than 0.01), 60 (p less than 0.05), and 120 (p less than 0.05) minutes after nifedipine. These results suggest that low renin hypertension is more critically dependent on extracellular calcium than are higher renin forms and demonstrate that levels of serum ionized calcium, plasma renin activity, or both may predict the sensitivity of blood pressure to calcium channel blockade. Lastly, calcium may play a pivotal role in vivo in coupling renin stimulation to adrenal aldosterone responses.

Effects of dehydroepiandrosterone sulfate on cellular calcium responsiveness and vascular contractility.

Dehydroepiandrosterone sulfate (DHEAS) is an endogenous steroid having a wide variety of biological effects, but its physiological role remains undefined. Since an age-related decline of DHEAS corresponds to the progressive onset of atherosclerosis, cardiovascular diseases, and overall mortality, we investigated a possible protective role of DHEAS in vascular disease by studying the effects of this hormone (10(-7) to 10(-5) mol/L) on cytosolic free calcium and contractility in different in vitro vascular tissue preparations. DHEAS produced a significant, dose-dependent relaxation of isolated helical strips of rat tail artery precontracted with KCl (60 mmol/L) (89.7 +/- 18.7%, P < .01), arginine vasopressin (3 nmol/L) (27.3 +/- 7.1%, P < .01), and norepinephrine (0.1 mumol/L) (49.2 +/- 18.2%, P < .01). In isolated vascular smooth muscle cells DHEAS reversibly inhibited KCl (30 mmol/L)-induced elevations of cytosolic free calcium to 69.8 +/- 8.4% and 43.8 +/- 7.4% of the control response at 5 x 10(-7) and 5 x 10(-6) mol/L, respectively (P < .05 at both doses). These results provide evidence of a direct vascular action of DHEAS, in doses reflecting circulating levels in vivo, and suggest the possibility that these effects are mediated by modulation of intracellular calcium metabolism. We hypothesize that physiologically, DHEAS may serve to buffer vascular responsiveness to a wide variety of depolarizing and constrictor hormonal stimuli.

Magnesium responsiveness to insulin and insulin-like growth factor I in erythrocytes from normotensive and hypertensive subjects.

Depletion of intracellular free magnesium (Mg(i)) is a characteristic feature of insulin resistance in essential hypertension, but it is not clear to what extent low Mg(i) levels contribute to insulin resistance, result from it, or both. As insulin-like growth factor I (IGF-I) may improve insulin resistance, we investigated whether this peptide could similarly improve Mg(i) responsiveness to insulin in hypertension, and whether this effect was related to any direct IGF-I effect on Mg(i). 31P-Nuclear magnetic resonance spectroscopy was used to measure Mg(i) in erythrocytes from 13 fasting normotensive and 10 essential hypertensive subjects before and 30, 60, and 120 min after incubation with a physiologically maximal dose of insulin (200 microU/mL) and with different doses of recombinant human IGF-I (0.1-100 nmol/L). In normotensive subjects, IGF-I elevated Mg(i) (P < 0.05) in a dose- and time-dependent fashion, as did insulin (P < 0.05). However, in hypertensive subjects, maximal Mg(i) responses to insulin, but not to IGF-I, were blunted [insulin, 163+/-11 to 177+/-10 micromol/L (P=NS); IGF-I, 164+/-6 to 190+/-11.7 micromol/L (P < 0.05)]. Furthermore, for insulin, but not for IGF-I, cellular Mg(i) responsiveness was closely and directly related to basal Mg(i) levels (insulin: r=0.72; P < 0.01; IGF-I: r=0.18; P=NS). Lastly, blunted Mg(i) responses to insulin could be reversed by preincubation of hypertensive cells with IGF-I. We conclude that 1) both IGF-I and insulin stimulate erythrocyte Mg(i) levels; 2) cellular Mg(i) responses to insulin, but not to IGF-I, depend on basal Mg(i) levels, i.e. the higher the Mg(i) the greater the sensitivity to insulin; and 3) IGF-I potentiates insulin-induced stimulation of Mg(i) at doses that themselves do not raise Mg(i). These effects of IGF-I may underlie at least in part its ability to improve insulin sensitivity clinically. Together, these data support a role for IGF-I in cellular magnesium metabolism and emphasize the importance of magnesium as a determinant of insulin action.

Effects of aging on serum ionized and cytosolic free calcium: relation to hypertension and diabetes.

Elevated cytosolic free calcium (Ca(i)) and reciprocally reduced, extracellular ionized calcium (Ca-ion) levels are observed in both hypertension and non-insulin-dependent diabetes mellitus (NIDDM). Because the changes of vascular function and insulin sensitivity in these conditions resemble the changes associated with "normal" aging, we wondered to what extent similar alterations in calcium metabolism occur with aging per se in the absence of overt hypertension or diabetes. We therefore measured platelet Ca(i) levels by spectrofluorometry and serum Ca-ion levels in normotensive, nondiabetic, healthy, normal, elderly (>65 years old) subjects, mean age +/-SEM, 72.2+/-1.5 years old (n=11); in healthy, normal, young (<65 years old) adults, 46.1+/-2.3 years old (n=12); in 10 young adult hypertensives, 48.6+/-1.9 years old; and in 10 normotensive NIDDM subjects, 49.2+/-1.6 years old. Platelet Ca(i) levels were higher (104.5+/-4.9 versus 80.2+/-1.8 nmol/L, P<0.01) and Ca-ion levels lower (1.212+/-0.010 versus 1.236+/-0.011 mmol/L, P<0.05) in normal elderly compared with young control subjects, but normal elderly Ca(i) and Ca-ion levels were indistinguishable from those in hypertensive (Ca(i) 107.5+/-3.6 nmol/L, Ca-ion 1.210+/-0.009 mmol/L) and NIDDM (Ca(i) 110.7+/-4.7 nmol/L, Ca-ion 1.204+/-0.014 mmol/L) subjects. In normal subjects, significant correlations were found between platelet Ca(i) levels and age (r=0.655, P<0.01) and between Ca(i) levels and systolic blood pressure (r=0.733, P<0.001). We conclude that aging is associated with alterations of Ca(i) and Ca-ion levels resembling those changes present at any age in hypertension and type 2 diabetes. We hypothesize that these alterations of calcium metabolism underlie the predisposition to the alterations of blood pressure and insulin sensitivity characteristic of "normal" aging. The data also suggest that studies of the aging process should be limited to subjects with normal blood pressure and glucose tolerance.

Altered ionic effects of insulin in hypertension: role of basal ion levels in determining cellular responsiveness.

To investigate the ionic actions of insulin in hypertension, 19F- and 31P-nuclear magnetic resonance spectroscopy were used to measure cytosolic free calcium (Ca(i)) and intracellular free magnesium (Mg(i)) levels in red blood cells from normal (n = 9) and hypertensive (n = 9) subjects before and 30, 60, 120, and 180 min after in vitro incubation with insulin. In hypertensive patients, basal Ca(i) levels were significantly higher (30.0 +/- 2.2 vs. 19.8 +/- 2.5 nmol/L; P < 0.05), and basal Mg(i) levels were significantly lower (170 +/- 10.9 vs. 209 +/- 8 micromol/L; P < 0.05) than in normotensive subjects. In normal cells, insulin significantly elevated Ca(i) to 39.8 +/- 8.0, 50.1 +/- 8.2, 69.3 +/- 11.1, and 50.9 +/- 13.4 nmol/L at 30, 60, 120, and 180 min and Mg(i) to 238 +/- 10,264 +/- 14,226 +/- 11, and 216 +/- 10 micromol/L at 30, 60, 120, and 180 min. In hypertensive subjects, the insulin-dependent Ca(i) elevation was blunted, and Mg(i) accumulation was completely suppressed. Continuous relationships were observed between basal values of each ion and insulin responses; the greater the Ca(i), the less the Ca(i) rose (r = -0.574; P = 0.013), and the lower the Mg(i), the less Mg(i) rose (r = 0.524; P = 0.025). Furthermore, a blunting of Mg(i) responses to insulin could be reproduced in normal cells that were magnesium depleted by prior treatment either with A23187 in a calcium-free medium or with high glucose concentrations (15 mmol/L). Once again, insulin responsiveness followed basal Mg(i) levels (r = 0.637; P < 0.001). Together, these data demonstrate ionic aspects of insulin resistance in hypertension and suggest that Ca(i) and Mg(i) levels may regulate cellular responsiveness to insulin. This may help to explain the different vascular actions attributed to insulin in normal compared with insulin-resistant states such as hypertension.

Effects of vitamin E and glutathione on glucose metabolism: role of magnesium.

Vitamin E is an antioxidant that has been demonstrated to improve insulin action. Glutathione, another natural antioxidant, may also be important in blood pressure and glucose homeostasis, consistent with the involvement of free radicals in both essential hypertension and diabetes mellitus. Our group has recently suggested that the effects of reduced glutathione on glucose metabolism may be mediated, at least in part, by intracellular magnesium levels (Mg([i])). Recent evidence suggests that vitamin E enhances glutathione levels and may play a protective role in magnesium deficiency-induced cardiac lesions. To directly investigate the effects of vitamin E supplementation on insulin sensitivity in hypertension, in relation to the effects on circulating levels of reduced (GSH) and oxidized (GSSG) glutathione and on Mg([i]), we performed a 4-week, double-blind, randomized study of vitamin E administration (600 mg/d) versus placebo in 24 hypertensive patients and measured whole-body glucose disposal (WBGD) by euglycemic glucose clamp, GSH/GSSG ratios, and Mg([i]) before and after intervention. The relationships among WBGD, GSH/GSSG, and Mg([i]) in both groups were evaluated. In hypertensive subjects, vitamin E administration significantly increased WBGD (25.56+/-0.61 to 31.75+/-0.53 micromol/kg of fat-free mass per minute; P<0.01), GSH/GSSG ratio (1.10+/-0.07 to 1.65+/-0.11; P<0.01), and Mg([i]) (1.71+/-0.042 to 1.99+/-0.049 mmol/L; P<0.01). In basal conditions, WBGD was significantly related to both GSH/GSSG ratios (r=0.58, P=0.047) and Mg([i]) (r=0.78, P=0.003). These data show a clinical link between vitamin E administration, cellular magnesium, GSH/GSSG ratio, and tissue glucose metabolism. Further studies are needed to explore the cellular mechanism(s) of this association.

Effects of glutathione on red blood cell intracellular magnesium: relation to glucose metabolism.

Recent evidence suggests that the endogenous antioxidant glutathione may play a protective role in cardiovascular disease. To directly investigate the role of glutathione in the regulation of glucose metabolism in hypertension, we studied the acute effects of in vivo infusions of this antioxidant (alone or in combination with insulin) on whole body glucose disposal (WBGD) using euglycemic glucose clamp and the effects on total red blood cell intracellular magnesium (RBC-Mg) in hypertensive (n=20) and normotensive (n=30) subjects. The relationships among WBGD, circulating reduced/oxidized glutathione (GSH/GSSG) levels, and RBC-Mg in both groups were evaluated. The in vitro effects of glutathione (100 micromol/L) on RBC free cytosolic magnesium (Mg(i)) were also studied. In vivo infusions of glutathione (15 mg/minx120 minutes) increased RBC-Mg in both normotensives and hypertensives (1.99+/-0.02 to 2.13+/-0.03 mmol/L, P<0.01, and 1.69+/-0.03 to 1.81+/-0.03 mmol/L, P<0.01, respectively). In vitro GSH but not GSSG increased Mg(i) (179+/-3 to 214+/-5 micromol/L, P<0.01). In basal conditions, RBC-Mg values were related to GSH/GSSG ratios (r=0.84, P<0.0001), and WBGD was directly, significantly, and independently related to both GSH/GSSG ratios (r=0.79, P<0.0001) and RBC-Mg (r=0.89, P<0.0001). This was also true when hypertensive and control groups were analyzed separately. On multivariate analysis, basal RBC-Mg (t=6.81, P<0.001), GSH/GSSG (t=3. 67, P<0.02), and blood pressure (t=2.89, P<0.05) were each independent determinants of WBGD, with RBC-Mg explaining 31% of the variability of WBGD. These data demonstrate a direct action of glutathione both in vivo and in vitro to enhance intracellular magnesium and a clinical linkage between cellular magnesium, GSH/GSSG ratios, and tissue glucose metabolism.

Cellular ions in hypertension, diabetes, and obesity. A nuclear magnetic resonance spectroscopic study.

To investigate the cellular basis linking hypertension, non-insulin-dependent diabetes mellitus (NIDDM), and obesity, we used 31P and 19F nuclear magnetic resonance spectroscopy to measure intracellular pH (pHi), free magnesium (Mgi), and cytosolic free calcium (Cai) in erythrocytes of obese and NIDDM subjects with and without hypertension. Compared with normotensive, nondiabetic controls (Cai, 25.2 +/- 1.4 nM; Mgi, 232 +/- 8 microM), Cai was elevated in both normotensive (36.8 +/- 2.7 nM, sig = 0.005) and hypertensive (43.4 +/- 2.9 nM, sig = 0.001) NIDDM subjects, and Mgi was concomitantly suppressed (normotensive: 206 +/- 11 microM, sig = 0.05; hypertensive: 196 +/- 8 microM, sig = 0.001). Similar but less striking changes were noted in obese subjects. Values of pHi were significantly lower (sig = 0.05) in all hypertensive groups compared with their normotensive controls. Continuous relations were observed for all subjects between Cai and diastolic blood pressure (r = 0.649, p less than 0.001) and body mass index (r = 0.565, p less than 0.001), between Mgi and diastolic blood pressure (r = -0.563, p less than 0.001) and fasting blood glucose (r = -0.580, p less than 0.001), and in diabetics, between pHi and diastolic blood pressure (r = -0.680, p less than 0.001). Thus, the constellation of elevated Cai and suppressed Mgi and pHi levels is characteristic of the hypertensive state. These abnormalities of cellular ion handling in whole or in part common to hypertension, diabetes, and obesity may contribute to the pathophysiology of these syndromes and may help to explain their frequent clinical coexistence.

Direct magnetic resonance determination of aortic distensibility in essential hypertension: relation to age, abdominal visceral fat, and in situ intracellular free magnesium.

To investigate the contribution of vascular compliance to essential hypertension (EH), we developed magnetic resonance imaging (MRI) techniques to directly measure aortic distensibility (AD) in the ascending and descending thoracic and abdominal aorta of fasting normal (n= 10) and EH (n=20) subjects. These results were compared with concurrent MR-based measurements of left ventricular mass index (LVMI) and abdominal subcutaneous and visceral fat and with 31P-MR spectroscopic measurement of in situ intracellular free magnesium levels (Mgi) in brain and skeletal muscle. Aortic distensibility in EH was consistently and significantly reduced at all measured sites (2.5+/-0.4, 2.2+/-0.4, 2.3+/-0.4 versus 7.0+/-1.6, 5.1+/-0.3, 7.3+/-0.8 mm Hg(-1) x 10(-3), P<.05), as was Mgi in the brain (284+/-22 versus 383+/-34 micromol/L, P<.05) and skeletal muscle (397+/-10 versus 527+/-36 micromol/L, P<.05). For all subjects, systolic blood pressure (r=-.662, P<.0001) and LVMI (r=-.484, P<.01) were inversely related to AD. AD and brain Mgi were inversely related to age (AD, r=-.792, P<.0001; brain Mgi: r=-.673, P<.05). AD was inversely related to fasting blood glucose (r=-.413, P<.05) and to abdominal visceral fat (r=-.416, P<.05) but not to body mass index (BMI: r=-.328, P=NS) or subcutaneous fat (r=-.157, P=NS). AD was also significantly and positively related to in situ Mgi, both in the brain and skeletal muscle (brain: r=.712, P<.01; skeletal muscle: r=.632, P<.01). We conclude that (1) MR techniques can be used to coordinately and noninvasively assess cardiac, vascular, metabolic, and ionic aspects of hypertensive disease in humans; (2) increased systolic blood pressure and LVMI in EH may at least in part result from decreased AD; (3) decreased Mgi contributes to arterial stiffness in hypertension and may help to explain the characteristic age-related decreases in AD; and (4) decreased AD may be one mechanism by which abdominal visceral fat contributes to cardiovascular risk.

Dietary compliance and cardiovascular risk reduction with a prepared meal plan compared with a self-selected diet.

Noncompliance with therapeutic diets remains a major obstacle to achieving improvements in cardiovascular disease (CVD) morbidity and mortality. This study compared dietary compliance and CVD risk factor response to two dietary interventions designed to treat hypertension, dyslipidemia, and diabetes mellitus. In a multicenter trial, 560 adults were randomly assigned to either a self-selected, mixed-food plan (n = 277), or a nutrient-fortified prepared meal plan (n = 283); each was designed to provide 15-20% of energy from fat, 55-60% from carbohydrate, and 15-20% from protein. Nutrient intake was estimated from 3-d food records collected biweekly throughout the 10-wk intervention. Compliance was determined by evaluating the participants' ability to meet specific criteria for energy intake [+/-420 kJ (100 kcal) from the midpoint of the prescribed energy range], fat intake (< 20%, < 25%, or < 30% of energy from total fat), and the National Cholesterol Education Program/American Heart Association Step 1 and 2 diet recommendations. Compliance with energy, fat, and Step 1 and 2 criteria was better in participants who followed the prepared meal plan than in those who followed the self-selected diet (P < 0.0001). Compliant participants in both groups achieved greater reductions in body weight, systolic and diastolic blood pressure, and total and low-density-lipoprotein cholesterol than noncompliant participants (P < 0.05). In general, better endpoint responses were observed with lower fat intakes regardless of group assignment. The prepared meal plan is a simple and effective strategy for meeting the many nutrient recommendations for CVD risk reduction and improving dietary compliance and CVD endpoints.

Improved quality of life in patients with generalized cardiovascular metabolic disease on a prepared diet.

Current dietary recommendation for cardiovascular disease risk reduction and recommended dietary allowances (RDAs) were used to develop a nutritionally complete prepackaged prepared meal plan specifically designed to reduce the risk of cardiovascular disease. In the current study we tested patient acceptance of the diet as defined by measures of quality of life. In a randomized, parallel-design, multicenter clinical trial, 77 persons with hypertension, diabetes mellitus, dyslipidemia, or a combination of two or more of these conditions were recruited and randomly assigned to either a prepared meal plan (n = 39) or a comparable self-selected diet (n = 38) for 10 wk. The prepared meal plan met both the RDAs for all essential micronutrients and the dietary recommendations of national health organizations for macronutrients, cholesterol, sodium, and fiber. The prescribed self-selected diet was matched for macronutrients. Quality of life, as measured by a battery of instruments, was the major endpoint. Individuals consuming the prepared meal plan had significant improvements in mental health (P < 0.01), general perceived health (P < 0.005), daily activities (P < 0.05), work performance (P < 0.005), affect (P < 0.01), and nutritional health perceptions (P < 0.001), and reductions in nutrition hassles based on a standardized questionnaire (P < 0.001). The self-selected-diet group had significant improvements in nutritional health perceptions (P < 0.001) and affect (P < 0.001). There were significant improvements in weight (P < 0.001), blood pressure (P < 0.001), cholesterol (P < 0.002), low-density lipoproteins (P < 0.001), glucose (P < 0.014), and glycated hemoglobin (Hb A(1c) (P < 0.004) that were comparable in both groups. In summary, this study shows that a nutritionally complete diet, whether prepackaged or self-selected, improves multiple risk factors for cardiovascular disease. The prepackaged prepared meal plan had the added benefit of a greater improvement in quality of life.