Significance of intracellular free calcium and magnesium and calcium-regulating hormones with sodium chloride loading in patients with essential hypertension

Calcium-Sensing Receptor (CaSR), Its Impact on Inflammation and the Consequences on Cardiovascular Health

The calcium Sensing Receptor (CaSR) is a cell surface receptor belonging to the family of G-protein coupled receptors. CaSR is mainly expressed by parathyroid glands, kidneys, bone, skin, adipose tissue, the gut, the nervous system, and the cardiovascular system. The receptor, as its name implies is involved in sensing calcium fluctuations in the extracellular matrix of cells, thereby having a major impact on the mineral homeostasis in humans. Besides calcium ions, the receptor is also activated by other di- and tri-valent cations, polypeptides, polyamines, antibiotics, calcilytics and calcimimetics, which upon binding induce intracellular signaling pathways. Recent studies have demonstrated that CaSR influences a wide variety of cells and processes that are involved in inflammation, the cardiovascular system, such as vascular calcification, atherosclerosis, myocardial infarction, hypertension, and obesity. Therefore, in this review, the current understanding of the role that CaSR plays in inflammation and its consequences on the cardiovascular system will be highlighted.

Pathways of hepatic and renal damage through non-classical activation of the renin-angiotensin system in chronic liver disease

In liver cirrhosis, renin-angiotensin system (RAS) activation sustains renal sodium retention and hepatic fibrogenesis. New information has recently enlivened the traditional concept of RAS. For instance, renin and prorenin bind their ubiquitous receptors, resulting in the local production of angiotensin (Ang) II; increased serum calcium and calcimimetic agents, through stimulation of extracellular calcium-sensing receptors (CaSR), blunt renin production and lead to natriuretic effects in human and experimental cirrhosis. Alongside systemic production, there is Ang II tissue production within various organs through RAS enzymes different from angiotensin-converting enzyme (ACE), that is chymase, tissue plasminogen activator and several cathepsins. In experimental cirrhosis, inhibition of chymase leads to natriuretic and hepatic antifibrotic effects, without changes in systemic haemodynamics. In the kidney, local RAS coordinates proximal and distal tubular sodium reabsorption. However, renalase, whose plasma and tissue levels are severely altered in experimental cirrhosis, degrades systemic and renal tubule catecholamines, antagonizing the effects of renal RAS. Angiotensinogen-derived natriuretic and vasodilating peptides (Ang1-9, Ang1-7, Ang3-8) and their receptors have been described. Receptor agonists or antagonists are available to affect portal hypertension and sodium retention in cirrhosis. ACE2-dependent generation of Ang1-7 may inhibit experimental liver fibrosis. inhibition of Ang1-7 clearance by means of neprilysin blockade has portal hypotensive and natriuretic effects. Ang1-12, whose production renin does not regulate, is converted to several different angiotensin peptides via chymase. Finally, Ang II behaves as either an antinatriuretic or a natriuretic agent, based on the tissue content of AT₁ R and AT₂ R receptors, their ratio being prone to pharmacological modulation.

Etiology and management of hypertension in chronic kidney disease

The kidneys are vital in the pathogenesis of hypertension and are also pathologically affected by the presence of hypertension. The prevalence of hypertension in chronic kidney disease (CKD) depends on age, the severity of renal failure, and proteinuria. The intricate and inextricable relationship between CKD and hypertension seems to cause cardiovascular disease that has assumed epidemic proportions. This article discusses the etiology and treatment of hypertension in CKD so that it can be better controlled.

Plasma 25-hydroxyvitamin D concentrations are inversely associated with blood pressure of Dahl salt-sensitive rats

Dietary salt is a contributing factor to the development of hypertension in individuals who are salt-sensitive. The vitamin D endocrine system has been reported to modulate vascular structure and function. Since elderly hypertensive females with low plasma renin activity, typical of salt-sensitivity, had significantly lower 25-hydroxyvitamin D concentrations compared with normotensive elderly and young females, we have used Dahl salt-sensitive and salt-resistant rats fed high (80 g/kg diet) and low (3 g/kg diet) salt diets as models to examine the relationship between salt-sensitivity and 25-hydroxyvitamin D, the precursor of the hormonal form of vitamin D, 1,25-dihydroxyvitamin D. Plasma 25-hydroxyvitamin D concentrations of salt-resistant rats were unaffected by a high salt diet, but plasma 25-hydroxyvitamin D concentrations of salt-sensitive rats were significantly reduced within three weeks to lower than 25%. There was a negative association between plasma 25-hydroxyvitamin D concentrations of salt-sensitive rats and the number of days that the rats were fed a high salt diet (r = -0.98, P < 0.02) and a positive association between blood pressure and the number of days that the rats were fed a high salt diet (r = 0.97, P < 0.05). An inverse relationship was found between plasma 25-hydroxyvitamin D concentrations and blood pressure (r = -0.99, P < 0.01). Spontaneously hypertensive rats did not have low plasma 25-hydroxyvitamin D concentrations, suggesting that reduction of plasma 25-hydroxyvitamin D concentration might be specific to salt-induced hypertension.

Effects of magnesium on blood pressure and intracellular ion levels of Brazilian hypertensive patients

Fifteen patients with uncomplicated mild to moderate primary hypertension (7 males, 8 females, age range 36-65 years) were submitted to a double blind randomized crossover study, receiving MgO 3 times a day at a daily dose of 1.0 g (600 mg/day of magnesium) and placebo for a period of 6 weeks. This was to test the effects of oral magnesium supplementation on blood pressure and sodium, potassium, calcium and magnesium intraerythrocyte concentrations. Concomitantly, plasma renin activity and serum aldosterone was also measured. Oral magnesium reduced significantly the systolic (delta = -7.6 mmHg, P < 0.05); diastolic (delta = -3.8 mmHg, P < 0.01) and mean blood pressure (delta = -5.9 mmHg, P < 0.01). After magnesium supplementation intraerythrocyte sodium concentration was reduced (delta = -0.55 mEq/l per cell, P < 0.01) and intraerythrocyte magnesium concentration was increased (delta = 1.20 mg/dl per cell, P < 0.01). The diminution of the blood pressure correlated positively with the reduction in intraerythrocyte sodium (r = 0.66, P < 0.01) after magnesium. However, our results have shown that the blood pressure response to oral magnesium was not homogeneous. Forty percent of our patients had their blood pressure effectively controlled (more than 10 mmHg reduction in mean blood pressure), being the hypotensive effect more evident in patients with recent hypertension and in those where the reduction in intraerythrocyte sodium was significantly greater than in the non-responder individuals. Intraerythrocyte potassium and calcium, serum aldosterone, plasma renin activity and urinary sodium excretion were maintained unchanged after magnesium supplementation. These data showed that oral magnesium supplementation may reduce the blood pressure, which can be partially explained by the decrease in intracellular sodium and augment in intracellular magnesium.

Parathyroid hypertensive factor predicts efficacy in the treatment of essential hypertension with verapamil

Parathyroid hypertensive factor (PHF) is a circulating hypertensive factor, levels of which are inversely related to renin profile. Given this relationship, it was hypothesized that a PHF level might serve as an alternate predictor of antihypertensive efficacy in hypertensive patients, avoiding the difficulties associated with renin profiling. To test this hypothesis, thirty patients with essential hypertension were placed on 240 mg once daily of a slow release verapamil preparation for a period of one month following a one month run-in period. Results showed an average reduction in mean arterial pressure (MAP)of -7 mmHg (range -5 to - 18) and an average reduction in PHF of -4 mmHg (range 7 to -28). Pre-treatment PHF level correlated with the blood pressure response to verapamil (r = -0.61, p = 0.0004). There was no correlation between any index of renin status and blood pressure. The only other correlation of note was between normalized, ionized calcium and change in blood pressure (r = -0.46, p =0.02). In a forward stepwise multivariate model with MAP as the dependent variable, PHF and normalized, ionized calcium levels were the only biochemical or demographic predictors of response to verapamil. These results suggest that PHF level may be useful in determining the initial choice of antihypertensive agent in hypertensive patients.

Calcium supplementation attenuates an enhanced platelet function in salt-loaded mildly hypertensive patients

We designed this study to evaluate the effect of low versus high calcium intake on platelet function in salt-loaded patients with mild hypertension. After a 7-day period of dietary salt restriction, 19 patients were placed on a high salt (300 mmol/d), low calcium (6.25 mmol/d) diet for 7 days; 10 of these patients were given 54 mmol/d of supplementary calcium, and 9 patients were given placebo. At the end of the low and high salt regimens, we evaluated changes in blood pressure, platelet aggregation, and the platelet release reaction measured as plasma beta-thromboglobulin and platelet factor 4 levels. With high salt intake, significant increases in mean blood pressure (P < .02), red blood cell sodium (P < .01), and platelet aggregation induced by 3 mumol/L ADP (P < .01) and by 3.0 mg/L epinephrine (P < .05) were observed in the placebo-treated patients but not in the calcium-supplemented ones. Compared with the placebo-treated patients, calcium-supplemented patients had a smaller weight gain (P < .05) but excreted more sodium and calcium (P < .01) at the end of the high salt regimen. Calcium supplementation resulted in decreases in beta-thromboglobulin (P < .05), platelet factor 4 (P < .01), and plasma and urinary excretions of norepinephrine (P < .02) during the high salt, low calcium regimen. The decrease in plasma norepinephrine correlated positively with the decreases in beta-thromboglobulin (r = .72, P < .02) and platelet factor 4 (r = .85, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Calcium and sodium handling during volume expansion in essential hypertension

To evaluate the actual role of extracellular fluid volume (ECFV) expansion per se in modulating the rate of urinary calcium excretion, a thermoneutral water immersion (WI) study was conducted in 10 normal subjects and 30 patients with essential hypertension. Central hypervolemia by 2 hours of WI caused a significant diuretic and natriuretic response (P < .005) in normal subjects; no significant changes were detected in urinary calcium and magnesium excretion. WI provoked either an appropriate or exaggerated natriuresis (P < .001) in 21 hypertensive patients; these subjects also exhibited a highly positive correlation between urinary sodium and calcium excretion during WI (P < .001). In the remaining nine hypertensive patients, WI produced a significant diuretic response, but a barely discernible (P = NS) natriuresis (inappropriate response). These subjects also exhibited a significant reduction of urinary calcium (P < .001) and magnesium (P < .01) excretion. The data indicate that (1) volume expansion per se may have a role in regulating calcium excretion in hypertensive subjects; (2) a calcium leak may be attributable to a close relationship between urinary sodium and calcium metabolism, and causally related to a disturbance of sodium and volume homeostasis in hypertension.