Altered aldosterone response to salt intake and angiotensin II infusion in young normotensive men with parental history of arterial hypertension

Influence of family history of hypertension on blood pressure and heart rate variability in young adults: a meta-analysis

PURPOUSE

This meta-analysis evaluates the impact of family history of hypertension (FHH + ) on blood pressure (BP) and heart rate variability (HRV) in young adults.

METHODS

Observational studies that evaluated adults (aged between 18 and 40 years) of both sexes, are without cardiometabolic disease diagnosis, are published in English, and are reporting on the influence of FHH + (father, mother, or both) on BP and HRV were included. In June 2021, we made a search of the electronic database MEDLINE (accessed by PubMed). Random-effects models were used, and data are reported as standardized mean difference and 95% confidence limits.

RESULTS

Thirty-eight studies with a total of 2025 individuals were included. Clinic systolic [3.13 mmHg (1.75-4.51)] and diastolic [2.85 mmHg (1.65-4.04)] BPs were higher ( P < 0.001) in individuals with an FHH + . Only 24-h systolic BP was higher [1.76 mmHg (0.05-3.47); P = 0.04] in individuals with an FHH + . As for HRV indices in time-domain, RMSSD: -7.00 ms (-10.75 to -3.26), SDNN: -13.93 ms (-23.56 to -4.30), and HF [-6.82 n. u. (-9.76 to -3.89)] were lower ( P < 0.05), and LF [4.78 ms (2.52-7.03)] and LF/HF ratio [0.32 (0.14-0.50)] were higher ( P < 0.001) in individuals with an FHH + .

CONCLUSION

FHH + negatively impacts BP and HRV in young adults.

Relationship Between the Aldosterone-to-Renin Ratio and Blood Pressure in Young Adults: A Longitudinal Study

[Figure: see text].

Association between salt taste sensitivity threshold and blood pressure in healthy individuals: a cross-sectional study

BACKGROUND

Hypertension is an important public health problem. Overweight and high salt intake are risk factors for its development.

OBJECTIVE

To evaluate the association between salt taste sensitivity threshold (STST) and blood pressure (BP) in healthy adults.

DESIGN AND SETTING

Cross-sectional study conducted in a private institution.

METHODS

104 healthy adults (aged 18-59 years) were evaluated. Sociodemographic, clinical and dietary data were collected. Nutritional status and BP were assessed using body mass index (BMI), waist circumference (WC), systolic blood pressure (SBP) and diastolic blood pressure (DBP). STST was assessed using graded saline solutions with sodium chloride concentrations ranging from 0.228 to 58.44 g/l. Identification of salty taste in solutions ≥ 3.652 g/l was used as the cutoff point for high STST.

RESULTS

Participants with high STST presented higher daily average intakes for energy (2017.4 ± 641.5 versus 1650.5 ± 357.7 kcal/day; P = 0.01) and sodium (3070.2 ± 1195.1 versus 2435.2 ± 963.6 mg/day; P = 0.01) and higher BMI (P = 0.008) and WC (P = 0.002). After adjustment for age, sex, sodium and potassium intake, WC and family history of hypertension, the averages for SBP and DBP in subjects with high STST were higher than in those with normal STST (SBP: 138.2 ± 1.7 versus 119.7 ± 0.9 mmHg; P < 0.001; DBP: 81.2 ± 1.9 versus 75.1 ± 1.0 mmHg; P = 0.008).

CONCLUSION

High STST was associated with elevated blood pressure in healthy adults, regardless of other risk factors for hypertension.

Increased Aldosterone Release During Head-Up Tilt in Early Primary Hypertension

BACKGROUND

Hyperaldosteronism is well known cause of secondary hypertension. However, the importance of aldosterone for the much larger group of patients with primary hypertension is less clear. We hypothesized that in young subjects with primary hypertension, the rise of plasma aldosterone levels in response to head-up tilt testing as a stress stimulus is exaggerated.

METHODS

Hemodynamics (blood pressure (BP), heart rate (HR), cardiac index (CI), and total peripheral vascular resistance index (TPRI), all by TaskForce monitor) and hormones (plasma renin activity (PRA), angiotensin II (Ang II), aldosterone) were measured before and during 30 minutes of head-up tilt in 45 young hypertensive and 45 normotensive subjects.

RESULTS

BP, HR, CI, and TPRI all increased in response to head-up tilt, with no difference between groups. There was no difference in baseline PRA, Ang II, and aldosterone between groups. During head-up tilt, PRA, and Ang II levels increased similarly. However, aldosterone levels increased to a greater extent in the hypertensive vs. normotensive subjects (P = 0.0021).

CONCLUSIONS

Our data suggest that an increased release of aldosterone in response to orthostatic stress is a feature of early primary hypertension. The similar increase in PRA and Ang II suggests a potential role for secretagogues of aldosterone other than Ang II in this response. In addition to its established role in secondary hypertension, dysregulation of aldosterone release might contribute to the development of primary arterial hypertension.

Celecoxib does not alter cardiovascular and renal function during dietary salt loading

1. Cyclo-oxygenase-2 (COX-2)-derived prostaglandins are important in controlling sodium excretion and renin release. In the present study, we tested the hypothesis that a clinical dose of celecoxib would impair urinary sodium excretion and elevate blood pressure (BP) during dietary salt loading. 2. Twelve normotensive individuals (mean (± SEM) age 35 ± 2 years) completed two separate 17 day dietary perturbations, one taking 200 mg/day celecoxib (CX2) and the other taking placebo (PL), randomized with a 1 month wash out. The controlled 17 day diet consisted of a 3 day run-in diet, 7 days of a low-salt (LS, 20 mmol sodium/day) diet and 7 days of a high-salt diet (HS, 350 mmol sodium/day) diet. The order in which the diets were applied was randomized. Data were collected on the last day of the LS and HS diets. 3. Plasma and urinary prostaglandins were modestly lower during celecoxib (P < 0.05). Urinary sodium excretion was greater (P < 0.01) during the HS diet (253 ± 10 vs 281 ± 27 mmol/24 h for PL vs CX2, respectively) compared with the LS diet (14 ± 3 vs 17 ± 7 mmol/24 h for PL vs CX2, respectively; P(drug) = 0.26). Celecoxib did not alter creatinine clearance (P > 0.50). Twenty-four hour mean arterial BP was similar during PL (87 ± 2 vs 87 ± 2 mmHg for LS and HS, respectively) and CX2 (88 ± 2 vs 87 ± 2 mmHg for LS and HS, respectively; P = 0.85), with no effect of dietary salt (P > 0.80). Plasma renin activity, angiotensin II and aldosterone were all suppressed with dietary salt loading (P < 0.05), with no effect of drug (P > 0.35). 4. In conclusion, blood pressure and renal function were not adversely affected by celecoxib, even during dietary salt loading. These findings support current guidelines suggesting minimal cardiovascular risks associated with short-term, low-dose use of celecoxib in young to middle-aged adults.

Eplerenone suppresses aldosterone/ salt-induced expression of NOX-4

INTRODUCTION

Salt-induced hypertension in the Dahl rat is associated with increases in angiotensin II, aldosterone, free radical generation and endothelial dysfunction. However, little is known about the specific mechanism(s) associated with the end-organ damage effects of aldosterone. We hypothesised that eplerenone reduces kidney damage by blocking nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity.

METHODS

Dahl salt-sensitive rats fed either a low-salt (LS) or high-salt (HS) diet were treated with aldosterone in the presence of eplerenone or apocynin. Indirect blood pressure was measured prior to start of diet and weekly thereafter. Levels of plasma nitric oxide (NO) and urinary 8-isoprostane were measured following treatment. Protein levels of selected subunits of NADPH were assessed by western blot.

RESULTS

Eplerenone and apocynin inhibited the rise in blood pressure induced by HS and/or aldosterone. This observation was accompanied with a parallel change in kidney protein levels of NADPH oxidase 4 (NOX-4) and p22phox. Aldosterone and high salt were associated with lower NO levels and greater renal oxidative stress.

CONCLUSIONS

NADPH oxidase is associated with the vascular and renal remodelling observed in high dietary salt intake. Aldosterone-induced expression of NOX-4 plays a pivotal role in the end-organ damage effect of aldosterone, as eplerenone tended to reduce kidney damage and inhibit NOX expression.

Aldosterone and arterial hypertension

In the setting of primary aldosteronism, elevated aldosterone levels are associated with increased blood pressure. Aldosterone concentrations within the normal range, however, can also alter blood pressure. Furthermore, the aldosterone-to-renin ratio, an indicator of aldosterone excess, is associated with hypertension, even in patients without excessive absolute aldosterone levels. In this Review we assess the data on the role of aldosterone in the development and maintenance of hypertension. We provide an overview of the complex crosstalk between genetic and environmental factors, and about aldosterone-mediated arterial hypertension and target organ damage. The discussion is organized according to major targets of aldosterone action: the collecting duct in the kidney, the vasculature and the central nervous system. The antihypertensive efficacy of mineralocorticoid-receptor blockers, even in patients with aldosterone values in the normal range, supports the evidence that aldosterone plays a part in blood pressure elevation in the absence of primary aldosteronism.

Aldosterone-receptor antagonism in hypertension

The role of the renin-angiotensin-aldosterone system (RAAS) in hypertension has since long been recognized and aldosterone has been acknowledged as one of the key hormones in the pathophysiology, not only in primary aldosteronism but also in essential hypertension and drug-resistant hypertension. Aldosterone-receptor antagonists (ARAs) are increasingly used in patients with resistant hypertension, often with impressive results. However, definitive evidence for the benefit of ARAs in these patients from randomized, controlled trials is lacking. This review gives an overview of the current data on this topic. Future studies should focus on the identification of factors that are able to predict the response to treatment, as to select patients who will benefit most from treatment with ARAs. On the basis of the current knowledge, we recommend prescription of ARAs to patients with primary aldosteronism, resistant hypertension and patients with hypertension and hypokalemia.

A novel-1364A/C aquaporin 5 gene promoter polymorphism influences the responses to salt loading of the renin-angiotensin-aldosterone system and of blood pressure in young healthy men

BACKGROUND

The family of aquaporin water channels contributes to water and salt homeostasis. AQP5 is a ubiquitously expressed exocrine-type water channel. Functional single nucleotide polymorphisms in AQP5 which alter gene transcription have not yet been described. We, therefore, sequenced the human AQP5 promoter to detect novel sequence variants which could impact upon AQP5 expression and contribute to the phenotypic variability of the renin-angiotensin-aldosterone system (RAAS).

METHOD AND RESULTS

Sequencing of the whole AQP5 promoter revealed a novel-1364A/C polymorphism. Substitution of C for A was associated with increased transcription factor binding as tested by electrophoretic mobility shift assay, but significantly reduced transcriptional activation of the AQP5 gene by cAMP and serum. The C allele was associated with significantly decreased mRNA in human heart and with decreased protein expression in erythrocyte membranes. Finally, we associated AQP5 genotypes with the variability of the RAAS in two independent study cohorts. First, we studied the phenotypic variability of the RAAS in 103 young (26 +/- 3 years) healthy males under an increased dietary salt intake. Increasing salt intake decreased plasma angiotensin II by 25% in AC/CC genotypes but only by 2% in AA genotypes (P = 0.012), and it decreased serum aldosterone by 34% in subjects with AC/CC genotypes but only by 19% in the AA genotypes (P = 0.005). Both genotypes had increased blood pressure under salt diet (P < 0.01), which was significantly more pronounced in AA genotypes (P = 0.029). Second, we investigated associations with variables of the RAAS in 96 old patients (68 +/- 10 years) with coronary artery disease scheduled for coronary artery bypass grafting. Aldosterone serum concentrations were 2-fold (P < 0.001) and angiotensin II plasma concentrations were 4-fold higher in AA genotypes than in AC/CC genotypes while ADH plasma concentrations did not differ.

CONCLUSION

A novel single nucleotide polymorphism in the AQP5 gene promoter alters AQP5 expression in different in vitro systems and cells, and is associated with alterations of variables of the RAAS both in young healthy males and in patients with coronary artery disease.

Effects of enalapril, tempol, and eplerenone on salt-induced hypertension in dahl salt-sensitive rats

The renin-angiotensin-aldosterone system (RAAS) has been implicated in the pathophysiology of salt-induced hypertension. Angiotensin converting enzyme inhibitors, angiotensin II-type 1 receptor blockers, and aldosterone receptor blockers are used to treat hypertension and congestive heart disease. In addition to their blood pressure lowering effects, they appear to protect against myocardial, renal, and vascular damage. In various models of hypertension, generation of reactive oxygen species is increased in the vasculature and that treatment with antioxidants or superoxide dismutase mimetics (e.g., tempol) improves vascular function and structure and reduces blood pressure. The purpose of this study was to examine the effects of enalapril, an angiotensin II converting enzyme inhibitor; eplerenone, a selective aldosterone receptor antagonist; and tempol, a superoxide dismutase mimetic, on salt-induced hypertension in Dahl Salt-Sensitive rats. The rats were placed on a high salt (HS; 8%) diet for 3 weeks prior to switching to a normal salt (0.3%) diet for an additional 3 weeks. While on the normal salt (NS) diet, rats were treated with enalapril (30 mg/kg/day in the drinking water), eplerenone (100 mg/kg/day by gavage), tempol (1 mM/day in the drinking water), eplerenone + enalapril, eplerenone + enalapril + tempol, or without drug treatment (control). After 3 weeks on HS diet, systolic blood pressure rose from 127 +/- 7 to 206 +/- 11 mm Hg and remained elevated when switched to NS diet. Subsequently, treatment with eplerenone alone or in combination with enalapril and tempol produced a stepwise reduction in systolic blood pressure reaching -80 mm Hg; however, enalapril and tempol alone produced more modest pressure reduction (approximately -35 mmHg). Plasma levels of prostacyclin and nitric oxide were elevated in rats treated with enalapril and eplerenone alone or in combination. Enalapril and eplerenone alone and in combination reduced heart and kidney levels of angiotensin II and aldosterone when compared with control. Renal and heart levels of reduced glutathione were diminished by eplerenone alone; however, enalapril tended to attenuate the effect of eplerenone on reduced glutathione levels in the heart. The findings from this study suggest that eplerenone reduces salt-induced hypertension by increasing endothelium-derived relaxing factors, inhibiting RAAS components and oxidative stress. (353words).

Alterations in aldosterone and angiotensin II levels in salt-induced hypertension

Several studies have demonstrated that plasma renin-angiotensin activity is reduced in rats administered a high salt diet. We evaluated changes in plasma and tissue levels of aldosterone (ALDO) and angiotensin II (A-II), as well as the reduced-to-oxidized glutathione ratio. Male Dahl salt-sensitive (SS) rats were placed on either a high-salt (8% NaCl; HS) or a normal-salt (0.3% NaCl; NS) diet for 3 weeks. Prior to and weekly on the diets, systolic blood pressure was measured by tail cuff plethysmography. Levels of A-II and ALDO in plasma, heart, and kidney were analyzed by enzyme immunoassay. Reduced and oxidized gluthatione were simultaneously measured by HPLC fluorescence detection. Heart and kidney tissues were prepared for histological analysis. Systolic blood pressure in animals on a HS diet was significantly elevated above that of those on a NS diet. High salt caused a reduction in both plasma A-II and ALDO levels; while their levels in the heart and kidney were increased. Exposure to a high-salt diet led to the enlargement of both heart and kidney. The reduced-to-oxidized glutathione ratio in plasma, heart and kidney was lowered by exposure to a HS diet. Kidneys from animals on a high-salt diet showed fibroid necrosis associated with wrinkling and thickening of the glomerular capillary wall, while hearts were hypertrophic. Taken together, high dietary salt induces inappropriate activation of the local renin-angiotensin-aldosterone systems. Tissue levels of angiotensin II and aldosterone may be more reflective of the severity of vascular maladaptations than are plasma levels, and may play a greater role in the maintenance of hypertension.

??-Adrenoceptor-mediated, nitric-oxide-dependent vasodilatation is abnormal in early hypertension

BACKGROUND

It is unknown whether beta-adrenoceptor-mediated vasodilatation is altered in early hypertension and whether it can be modulated by L-arginine.

METHODS AND DESIGN

We measured changes in forearm blood flow by plethysmography in response to acetylcholine (9 and 37 microg/min), sodium nitroprusside (200 and 800 ng/min) and the beta-receptor agonist, isoproterenol (50 and 200 ng/min) in 12 patients with essential hypertension (group EH) and in healthy volunteers with (group PFH; n = 14) and without (group NFH; n = 14) a family history of essential hypertension, before and during concomitant infusion of L-arginine (10 micromol/min). In five individuals from each group, infusion of acetylcholine and isoproterenol was repeated during the concurrent blockade of nitric oxide synthesis by N-monomethyl-L-arginine (L-NMMA; 4 micromol/min).

RESULTS

The response to acetylcholine was reduced in groups EH and PFH compared with group NFH (both P < 0.05), whereas the vasodilator effects of isoproterenol and sodium nitroprusside were similar in all three groups. Acetylcholine- and isoproterenol-induced vasodilatation did not change during infusion of the nitric oxide precursor, L-arginine, in group NFH, but were significantly enhanced by L-arginine in groups PFH and EH [forearm blood flow before and after isoproterenol 200 ng/min: group PFH 11.8 +/- 1.02 and 13.3 +/- 1.08 ml/min, respectively (P < 0.05); group EH: 11.3 +/- 1.57 and 14.9 +/- 1.91 ml/min, respectively (P < 0.01)]. Co-infusion of L-NMMA blunted the response to acetylcholine and isoproterenol in group NFH (P < 0.05), but did not significantly modify vasodilatation in groups PFH and EH.

CONCLUSIONS

Although beta-adrenergic vasodilatation seemed to be unaltered in early hypertension, L-arginine enhanced the response to isoproterenol, whereas concomitant inhibition of nitric oxide synthase by L-NMMA had no significant effect. These findings suggest that the nitric oxide component of isoproterenol-mediated vasodilatation is impaired in early hypertension and possibly compensated by increased beta-adrenoceptor responsiveness of smooth muscle cells. In this setting, supplementation of the nitric oxide precursor, L-arginine, enhances the vasodilator response to beta-adrenergic stimulation.

Effects of truncated angiotensins in humans after double blockade of the renin system

Angiotensins different from ANG II exhibit biological activities, possibly mediated via receptors other than ANG II receptors. We studied the effects of 3-h infusions of ANG III, ANG-(1-7), and ANG IV in doses equimolar to physiological amounts of ANG II (3 pmol. kg-1. min-1), in six men on low-sodium diet (30 mmol/day). The subjects were acutely pretreated with canrenoate and captopril to inhibit aldosterone actions and ANG II synthesis, respectively. ANG II infusion increased plasma angiotensin immunoreactivity to 53 +/- 6 pg/ml (+490%), plasma aldosterone to 342 +/- 38 pg/ml (+109%), and blood pressure by 27%. Glomerular filtration rate decreased by 16%. Concomitantly, clearance of endogenous lithium fell by 66%, and fractional proximal reabsorption of sodium increased from 77 to 92%; absolute proximal reabsorption rate of sodium remained constant. ANG II decreased sodium excretion by 70%, potassium excretion by 50%, and urine flow by 80%, whereas urine osmolality increased. ANG III also increased plasma aldosterone markedly (+45%), however, without measurable changes in angiotensin immunoreactivity, glomerular filtration rate, or renal excretion rates. During vehicle infusion, plasma renin activity decreased markedly ( approximately 700 to approximately 200 mIU/l); only ANG II enhanced this decrease. ANG-(1-7) and ANG IV did not change any of the measured variables persistently. It is concluded that 1) ANG III and ANG IV are cleared much faster from plasma than ANG II, 2) ANG II causes hypofiltration, urinary concentration, and sodium and potassium retention at constant plasma concentrations of vasopressin and atrial natriuretic peptide, and 3) a very small increase in the concentration of ANG III, undetectable by usual techniques, may increase aldosterone secretion substantially.

Reduced activity of the kallikrein-kinin system predominates over renin-angiotensin system overactivity in all conditions of sodium balance in essential hypertensives and family-related hypertension

OBJECTIVE

To study the renin-angiotensin-aldosterone and kallikrein-kinin systems in essential hypertensives and offspring of hypertensive parents during different sodium loads, and to explore their possible influence on renal hemodynamics.

METHODS

Forty-five essential hypertensives (35 +/- 4 years old, 25 males), 30 offspring of hypertensive parents (26 +/- 8 years old, 16 males) and 30 normotensive controls (28 +/- 5 years old, 20 males) were submitted to three different sodium loads (high, 250 mmol/l; normal, 140 mmol/l; and low, 20 mmol/l). Blood pressure, plasma renin activity, serum aldosterone, total kallikrein and urinary kallikrein-like activity were measured after each period. Effective renal plasma flow and glomerular filtration rate were also measured. In essential hypertensive subjects, renal hemodynamic and hormonal parameters were also measured after 3 days of 20 mg enalapril administration.

RESULTS

Plasma renin activity and serum aldosterone were higher in normotensives, essential hypertensives and offspring of hypertensive parents only during low sodium intake, whereas urinary kallikrein activity was lower in hypertensive offspring and essential hypertensives, compared with normotensives, during the three diet conditions. Effective renal plasma flow was found to be reduced in hypertensives and normotensive offspring, while the glomerular filtration rated was similar in the three groups. Angiotensin converting enzyme inhibitor (ACEI) administration to essential hypertensives for 3 days normalized effective renal plasma flow, increased plasma renin activity and decreased aldosterone and urinary kallikrein activity.

CONCLUSIONS

Our observations confirmed the presence of a hormonal imbalance between the renin-angiotensin-aldosterone system and the kallikrein-kinin system, not only in essential hypertensives but also in the offspring of hypertensive parents. This imbalance probably affects the renal circulation and sodium homeostasis, since there was reduced effective renal plasma flow in both populations compared with normotensive subjects. The positive effect of ACEI, resulting in normalization of the effective renal plasma flow in essential hypertensive patients, suggests the involvement of both systems in impaired renal circulation.

Dietary salt and hypertension: a scientific issue or a matter of faith?

Many workers have an overly simplistic view of the relationship between salt intake and hypertension. This article attempts a critical evaluation of some of the evidence.

Aldosterone: a risk factor for vascular disease

Blockade of the renin-angiotensin-aldosterone system with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor antagonists has resulted in beneficial effects in essential hypertensive patients. However, occurrence of cardiovascular events has not been appropriately controlled beyond a certain percentage. One reason could be the effects of aldosterone, the final component of the system. The aldosterone escape phenomenon could explain undesirable outcomes observed in hypertensive patients even under treatment with ACE inhibitors or angiotensin antagonists. Aldosterone has direct effects on the vasculature and has been associated with vascular smooth muscle cell hypertrophy, endothelial dysfunction, cardiac fibrosis, proteinuria, and renal vascular injury. Animal models and clinical trials have proven the benefit of aldosterone receptor antagonism. With increased recognition of the prevalence of hyperaldosteronism in patients thought to have "essential" hypertension, the use of drugs that block aldosterone action may become more widespread and protect the vasculature from the deleterious effects of aldosterone.

Functional relevance of aldosterone for the determination of left ventricular mass

In experimental studies, the importance of aldosterone for the development of left ventricular (LV) hypertrophy has been demonstrated. In 120 healthy Caucasian men (aged 25 +/- 3 years; blood pressure, 134 +/- 15/86 +/- 12 mm Hg), we determined LV mass (2-dimensionally guided M-mode echocardiography), urinary aldosterone concentration, and the response of aldosterone to angiotensin II infusion (3.0 ng/kg/min). Seventy-six volunteers took part in a follow-up visit after 2 years when urinary aldosterone concentration and LV mass were determined again. At follow-up, LV mass increased in 42 subjects (by 33 +/- 26 g), whereas in 34 subjects LV mass decreased (by 27 +/- 22 g). Between the 2 groups, only the change in urinary aldosterone concentration over time was significantly different (group with increased LV mass had an increase in urinary aldosterone concentration by 2.5 +/- 5.4 microg/day; group with decreased LV mass had a decrease in urinary aldosterone concentration by 0.7 +/- 4.6; p <0.01 between groups). In accordance, we found significant correlations between changes in LV mass and changes in urinary aldosterone concentration (r = 0.29, p <0.05) and between changes in LV mass and the response of aldosterone to angiotensin II at baseline (r = 0.25, p <0.05). Both changes in aldosterone concentration over time and the response of aldosterone to angiotensin II were related to changes in LV mass over time. These data underscore the importance of aldosterone for the development of LV hypertrophy. This process is already evident in young subjects with apparently small changes in LV mass over a mean follow-up period of 2 years.

Contrasting associations between aldosterone synthase gene polymorphisms and essential hypertension in blacks and in whites

BACKGROUND

Genetic variability in the gene for aldosterone synthase--a key enzyme in the production of aldosterone--can affect sodium homeostasis and thereby blood pressure. The possibility of impaired aldosterone production for the development of hypertension is of particular relevance in black Afro-Caribbeans exposed to a high dietary sodium intake.

OBJECTIVES

To compare the frequency of three variants (-344C/T, intron 2 conversion, and the K173R polymorphism) of the aldosterone synthase gene in blacks and whites, and to determine any association of the variants with hypertension.

DESIGN AND METHODS

We made case-control comparisons of the three gene variants in relation to ethnic background and to essential hypertension in 193 white (51% hypertensive) and 245 black individuals (59% hypertensive) living in south London.

RESULTS

The frequency of each of the variants was significantly different between the two ethnic groups. The T and the K alleles were more frequent in the black participants (79 compared with 50% for the -344T allele and 81 compared with 50% for K173 allele), whereas the frequency of the intron 2 conversion allele was much lower in that group (8 compared with 38%). None of these variants was associated with essential hypertension in the black participants. In contrast, in the white participants there was a significant and graded association between the intron 2 conversion allele and essential hypertension (odds ratio 1.86, 95% confidence interval 1.16 to 2.98; = 0.01). Moreover, among the white population, the presence of homozygosity both of the T allele and of the intron 2 conversion alleles was associated with a much greater frequency of hypertension (71 compared with 43%; chi(2) = 0.03).

CONCLUSIONS

The contrasting associations between these variants and essential hypertension do not necessarily exclude the possibility that other, as yet undefined, variants of the aldosterone synthase gene could be linked with hypertension in black people. Nonetheless, the strong association between the intron 2 conversion allele and essential hypertension in the white population reinforces the view that the increased blood pressure may be due, at least in part, to abnormal expression of enzymes involved in the metabolism of adrenal mineralocorticoids.

Resistance artery mechanics and composition in angiotensin II-infused rats: effects of aldosterone antagonism

BACKGROUND

Angiotensin (Ang) II stimulates aldosterone production, which may mediate some of the effects of Ang II.

OBJECTIVE

To test whether Ang II-induced structural and mechanical changes in resistance arteries may be prevented by the non-selective aldosterone receptor blocker, spironolactone, independently of reduction in blood pressure.

METHODS

Male Sprague-Dawley rats received Ang II [120 ng/kg per min subcutaneously (s.c.)] with or without spironolactone or hydralazine (25 mg/kg per day). Two additional groups received aldosterone (750 ng/h s.c.) with or without spironolactone. After 2 weeks, third-order mesenteric arteries were dissected and studied by pressurized myograph. Deposition of collagen type I/III in the vascular wall was evaluated by confocal immunofluorescence microscopy.

RESULTS

Ang II increased blood pressure significantly (P <0.01); this was partially prevented by spironolactone (P <0.01) and nearly normalized by hydralazine (P <0.01). Media thickness, media:lumen ratio and media cross-sectional area of mesenteric resistance arteries increased under Ang II or aldosterone (P <0.01) and this was partially prevented by spironolactone (P <0.01), but not by hydralazine. Compared with the control or Ang II + spironolactone groups, rats treated with Ang II with or without hydralazine presented stiffer vessels, with leftward shift of the stress-strain relationship and a raised slope of the incremental elastic modulus-stress relationship (P <0.05). Confocal microscopy demonstrated enhanced deposition of collagen type I/III in the media of arteries from rats infused with Ang II or aldosterone, an effect that was prevented partially by spironolactone but unaffected by hydralazine.

CONCLUSION

Ang II-induced vascular alterations in structure, mechanics and composition were partially prevented by spironolactone, independently of blood pressure reduction, providing further evidence that some actions of Ang II on resistance arteries are mediated by aldosterone.