Abnormal renal sodium handling in essential hypertension. Relation to failure of renal and adrenal modulation of responses to angiotensin II

Normative values of renin and aldosterone in clinically stable preterm neonates

BACKGROUND

There is a paucity of literature on the normative levels of plasma renin concentration (PRC) and serum aldosterone (SA) in premature neonates. This study aims to provide normative data on PRC and SA levels in preterm neonates in the first 2 weeks after birth and explore associations with maternal, perinatal, or postnatal factors.

METHODS

Neonates born at 26- to 34-week gestation were recruited from two neonatal intensive care units in Canada and Australia. The direct renin assay PRC and SA were analyzed on day 1 and days 14-21 after birth to compare across categorical variables and to produce normative values.

RESULTS

A total of 262 subjects were enrolled from the Canadian (29%) and Australian (71%) sites. The mean gestational age was 30 weeks, with a mean birth weight of 1457 g. The normative values of PRC and SA for neonates born between 26 + 0 and 29 + 6 weeks and 30 + 0 and 34 + 0 weeks of gestation were produced for day 1 and day 14-21 after birth. Both PRC and SA increased from day 1 to day 14-21. The more premature neonates reached a higher PRC on days 14-21 after birth but exhibited lower SA levels on day 1 after birth. When comparing gender, birth weight, and maternal risk factor categories, no statistical differences in PRC or SA were found. A small but significant decrease in PRC, but not SA, was noted for neonates with placental pathology.

CONCLUSIONS

This study produced normative values of PRA and SA in clinically stable preterm neonates that can be referenced for use in clinical practice. A higher resolution version of the Graphical abstract is available as Supplementary information.

Blunted natriuretic response to saline loading in sheep with hypertensive kidney disease following radiofrequency catheter-based renal denervation

Renal sympathetic nerves contribute to renal excretory function during volume expansion. We hypothesized that intact renal innervation is required for excretion of a fluid/electrolyte load in hypertensive chronic kidney disease (CKD) and normotensive healthy settings. Blood pressure, kidney hemodynamic and excretory response to 180 min of isotonic saline loading (0.13 ml/kg/min) were examined in female normotensive (control) and hypertensive CKD sheep at 2 and 11 months after sham (control-intact, CKD-intact) or radiofrequency catheter-based RDN (control-RDN, CKD-RDN) procedure. Basal blood pressure was ~ 7 to 9 mmHg lower at 2, and 11 months in CKD-RDN compared with CKD-intact sheep. Saline loading did not alter glomerular filtration rate in any group. At 2 months, in response to saline loading, total urine and sodium excretion were ~ 40 to 50% less, in control-RDN and CKD-RDN than intact groups. At 11 months, the natriuretic and diuretic response to saline loading were similar between control-intact, control-RDN and CKD-intact groups but sodium excretion was ~ 42% less in CKD-RDN compared with CKD-intact at this time-point. These findings indicate that chronic withdrawal of basal renal sympathetic activity impairs fluid/electrolyte excretion during volume expansion. Clinically, a reduced ability to excrete a saline load following RDN may contribute to disturbances in body fluid balance in hypertensive CKD.

Sex-specific differences in endoplasmic reticulum aminopeptidase 1 modulation influence blood pressure and renin-angiotensin system responses

Salt sensitivity of blood pressure (SSBP) and hypertension are common, but the underlying mechanisms remain unclear. Endoplasmic reticulum aminopeptidase 1 (ERAP1) degrades angiotensin II (ANGII). We hypothesized that decreasing ERAP1 increases BP via ANGII-mediated effects on aldosterone (ALDO) production and/or renovascular function. Compared with WT littermate mice, ERAP1-deficient (ERAP1+/-) mice had increased tissue ANGII, systolic and diastolic BP, and SSBP, indicating that ERAP1 deficiency leads to volume expansion. However, the mechanisms underlying the volume expansion differed according to sex. Male ERAP1+/- mice had increased ALDO levels and normal renovascular responses to volume expansion (decreased resistive and pulsatility indices and increased glomerular volume). In contrast, female ERAP1+/- mice had normal ALDO levels but lacked normal renovascular responses. In humans, ERAP1 rs30187, a loss-of-function gene variant that reduces ANGII degradation in vitro, is associated with hypertension. In our cohort from the Hypertensive Pathotype (HyperPATH) Consortium, there was a significant dose-response association between rs30187 risk alleles and systolic and diastolic BP as well as renal plasma flow in men, but not in women. Thus, lowering ERAP1 led to volume expansion and increased BP. In males, the volume expansion was due to elevated ALDO with normal renovascular function, whereas in females the volume expansion was due to impaired renovascular function with normal ALDO levels.

Association between preterm birth and the renin-angiotensin system in adolescence: influence of sex and obesity

OBJECTIVES

Preterm birth appears to contribute to early development of cardiovascular disease, but the mechanisms are unknown. Prematurity may result in programming events that alter the renin-angiotensin system. We hypothesized that prematurity is associated with lower angiotensin-(1-7) in adolescence and that sex and obesity modify this relationship.

METHODS

We quantified angiotensin II and angiotensin-(1-7) in the plasma and urine of 175 adolescents born preterm and 51 term-born controls. We used generalized linear models to estimate the association between prematurity and the peptides, controlling for confounding factors and stratifying by sex and overweight/obesity.

RESULTS

Prematurity was associated with lower plasma angiotensin II (β: -5.2 pmol/l, 95% CI: -10.3 to -0.04) and angiotensin-(1-7) (-5.2 pmol/l, 95% CI: -8.4 to -2.0) but overall higher angiotensin II:angiotensin-(1-7) (3.0, 95% CI: 0.9-5.0). The preterm-term difference in plasma angiotensin-(1-7) was greater in women (-6.9 pmol/l, 95% CI: -10.7 to -3.1) and individuals with overweight/obesity (-8.0 pmol/l, 95% CI: -12.2 to -3.8). The preterm-term difference in angiotensin II:angiotensin-(1-7) was greater among those with overweight/obesity (4.4, 95% CI: 0.6-8.1). On multivariate analysis, prematurity was associated with lower urinary angiotensin II:angiotensin-(1-7) (-0.13, 95% CI: -0.26 to -0.003), especially among the overweight/obesity group (-0.38, 95% CI: -0.72 to -0.04).

CONCLUSION

Circulating angiotensin-(1-7) was diminished whereas urinary angiotensin-(1-7) was increased relative to angiotensin II in adolescents born preterm, suggesting prematurity may increase the risk of cardiovascular disease by altering the renin-angiotensin system. Perinatal renin-angiotensin system programming was more pronounced in women and individuals with overweight/obesity, thus potentially augmenting their risk of developing early cardiovascular disease.

Genetics of Human Primary Hypertension: Focus on Hormonal Mechanisms

Increasingly, primary hypertension is being considered a syndrome and not a disease, with the individual causes (diseases) having a common sign-an elevated blood pressure. To determine these causes, genetic tools are increasingly employed. This review identified 62 proposed genes. However, only 21 of them met our inclusion criteria: (i) primary hypertension, (ii) two or more supporting cohorts from different publications or within a single publication or one supporting cohort with a confirmatory genetically modified animal study, and (iii) 600 or more subjects in the primary cohort; when including our exclusion criteria: (i) meta-analyses or reviews, (ii) secondary and monogenic hypertension, (iii) only hypertensive complications, (iv) genes related to blood pressure but not hypertension per se, (v) nonsupporting studies more common than supporting ones, and (vi) studies that did not perform a Bonferroni or similar multiassessment correction. These 21 genes were organized in a four-tiered structure: distant phenotype (hypertension); intermediate phenotype [salt-sensitive (18) or salt-resistant (0)]; subintermediate phenotypes under salt-sensitive hypertension [normal renin (4), low renin (8), and unclassified renin (6)]; and proximate phenotypes (specific genetically driven hypertensive subgroup). Many proximate hypertensive phenotypes had a substantial endocrine component. In conclusion, primary hypertension is a syndrome; many proposed genes are likely to be false positives; and deep phenotyping will be required to determine the utility of genetics in the treatment of hypertension. However, to date, the positive genes are associated with nearly 50% of primary hypertensives, suggesting that in the near term precise, mechanistically driven treatment and prevention strategies for the specific primary hypertension subgroups are feasible.

Obesity is Associated with Higher Blood Pressure and Higher Levels of Angiotensin II but Lower Angiotensin-(1-7) in Adolescents Born Preterm

OBJECTIVES

To evaluate if obesity is associated with increased angiotensin II (Ang II) and decreased angiotensin-(1-7) or Ang-(1-7) in the circulation and urine among adolescents born prematurely.

STUDY DESIGN

In a cross-sectional analysis of 175 14-year-olds born preterm with very low birth weight, we quantified plasma and urinary Ang II and Ang-(1-7) and compared their levels between subjects with overweight/obesity (body mass index ≥85th percentile, n = 61) and those with body mass index <85th percentile (n = 114) using generalized linear models, adjusted for race and antenatal corticosteroid exposure.

RESULTS

Overweight/obesity was associated with higher systolic blood pressure and a greater proportion with high blood pressure. After adjustment for confounders, overweight/obesity was associated with an elevated ratio of plasma Ang II to Ang-(1-7) (β: 0.57, 95% CI 0.23-0.91) and higher Ang II (β: 0.21 pmol/L, 95% CI 0.03-0.39) but lower Ang-(1-7) (β: -0.37 pmol/L, 95% CI -0.7 to -0.04). Overweight/obesity was associated with a higher ratio of urinary Ang II to Ang-(1-7) (β: 0.21, 95% CI -0.02 to 0.44), an effect that approached statistical significance.

CONCLUSIONS

Among preterm-born adolescents, overweight/obesity was associated with increased Ang II but reduced Ang-(1-7) in the circulation and the kidney as well as higher blood pressure. Obesity may compound the increased risk of hypertension and cardiovascular disease in individuals born prematurely by further augmenting the prematurity-associated imbalance in the renin-angiotensin system.

Biological Sex Modulates the Adrenal and Blood Pressure Responses to Angiotensin II

The relationship between biological sex and aldosterone on blood pressure (BP) is unclear. We hypothesized that sex would modify the interaction between aldosterone and vascular responses to salt intake and angiotensin II (AngII). To test this hypothesis, in 1592 subjects from the well-controlled Hypertensive Pathotype cohort, we compared responses of women and men to chronic (BP and aldosterone levels in response to dietary salt) and acute (BP, renal plasma flow, and aldosterone responses to AngII infusion) manipulations. Women had a 30% higher salt sensitivity of BP than men (P<0.0005) regardless of age or hypertension status, a greater BP response to AngII, and a 15% greater aldosterone response to AngII on both restricted and liberal salt diets (P<0.005). Furthermore, there was an interaction (P=0.003) between sex and aldosterone on BP response to AngII. Women also had a greater (P<0.01) increment in renal plasma flow in response to AngII than men. To assess potential mechanisms for this sex effect, we compared aldosterone responses to AngII or potassium from rat zona glomerulosa cells and observed greater aldosterone production in female than male zona glomerulosa cells basally and in response to both agonists (P<0.0001). In a rodent model of aldosterone-mediated cardiovascular disease induced by increased AngII and low NO, circulating aldosterone levels (P<0.01), myocardial damage (P<0.001), and proteinuria (P<0.05) were greater in female than male rats despite having similar BP responses. Thus, increased aldosterone production likely contributes to sex differences in cardiovascular disease, suggesting that women may be more responsive to mineralocorticoid receptor blockade than men.

Race, obesity, and the renin-angiotensin-aldosterone system: treatment response in children with primary hypertension

BACKGROUND

Pediatric primary hypertension (HTN) is increasingly recognized, but the effect of patient characteristics such as obesity and race on treatment outcomes is not well described. The renin-angiotensin-aldosterone system (RAAS) may also contribute to HTN. We hypothesized patient parameters of these factors, including baseline RAAS, influence blood pressure (BP) response to pharmacological treatment in HTN.

METHODS

This was a retrospective cohort of 102 consecutive patients with HTN. Primary outcomes were changes per year in systolic and diastolic BP (SBP, DBP). Secondary outcome was change per year in left ventricular mass index (LVMI). We evaluated whether baseline plasma renin activity (PRA), aldosterone, renin-to-aldosterone ratio, overweight/obesity, race, initial drug choice, and multidrug therapy were associated with the outcomes using general linear regression models adjusted for confounding variables.

RESULTS

Racially diverse (43% Hispanic, 28% black, 25% white) and predominantly overweight/obese (75%) patients were studied. Median length of follow-up was 14.5 months. Higher baseline aldosterone was associated with decreased SBP (-1.03 mmHg/year), DBP (-0.95 mmHg/year), and DBP z score (-0.07/year) during the study period. Higher baseline PRA was associated with decreased SBP z score (-0.04/year) and LVMI (-2.89 g/m^2.7/year). Stratified analyses revealed the relationships between baseline aldosterone and PRA, and annual reductions in outcomes were strengthened in nonobese and white patients.

CONCLUSIONS

Pretreatment aldosterone and PRA predicted short-term follow-up BP and LVMI, especially in nonobese and white patients. The RAAS profile could guide treatment of HTN and suggests consideration of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers as first-line treatment options.

Oxidative stress causes imbalance of renal renin angiotensin system (RAS) components and hypertension in obese Zucker rats

Background

Oxidative stress plays an important role in the pathogenesis of hypertension, especially in obesity‐related hypertension. The natriuretic and antinatriuretic components of the renal renin angiotensin system (RAS) maintain sodium homeostasis and blood pressure. Here, we test the hypothesis that increased oxidative stress leads to the imbalance of RAS components and hypertension in obese Zucker rats.

Methods and Results

Lean and obese rats received vehicle or tempol, a superoxide dismutase mimetic in the drinking water for 4 weeks. Compared with vehicle‐treated lean rats, vehicle‐treated obese rats exhibited higher blood pressure and increased renal oxidative stress, accompanied by increased diuretic and natriuretic responses to AT₁R antagonist (Candesartan) and AT₂R agonist (CGP‐42112A) and reduced diuretic and natriuretic response to MasR agonist (Ang‐[1 to 7]). Moreover, obese rats had higher ACE, AT₁R and AT₂R, lower ACE2 and MasR expressions in the kidney. All of the above‐mentioned abnormalities were reversed to some degree by tempol treatment. In primary cultures of renal proximal tubular (RPT) cells from lean and obese rats, tempol treatment also increased AT₂R, ACE2, and MasR expressions but decreased AT₁R and ACE expressions in obese rats.

Conclusions

Taken together, our study indicated that the imbalance of renal RAS components was associated with increased oxidative stress in obese rats. Furthermore, antioxidant treatment with tempol reversed the imbalance of renal RAS components and led to diuresis and natriuresis, which, at least in part, explains the blood pressure‐lowering effect of antioxidant supplementation in obesity‐related hypertension.

Role of mineralocorticoid receptor antagonists in cardiovascular disease

Aldosterone exerts its best known sodium homeostasis actions by controlling sodium excretion at the level of the distal tubules via activation of the apical epithelial sodium channel and the basolateral Na(+)/K(+)ATPase pump. Recently, this mineralocorticoid hormone has been demonstrated to act on the heart and blood vessels. Excess release of aldosterone in relation to the salt status induces both genomic and nongenomic effects that by promoting endothelial dysfunction, and vascular and cardiorenal adverse remodeling, contribute to the target organ damage found in hypertension, heart failure, myocardial infarction, and chronic renal failure. Mineralocorticoid receptor blockers have been shown to be highly effective in resistant hypertension and to slow down heart failure progression, and in experimental animals, the development of atherosclerosis. Blockade of the action of aldosterone and potentially other mineralocorticoid steroids has been increasingly demonstrated to be an extremely beneficial therapy in different forms of cardiovascular disease. This review provides a summary of the knowledge that exists on aldosterone actions in the cardiovascular system and, in providing the translational impact of this knowledge to the clinical arena, illustrates how much more needs to be achieved in exploring the use of mineralocorticoid receptor blockers in less advanced stages of heart, renal, and vascular disease.

Loss of a kidney during fetal life: long-term consequences and lessons learned

Epidemiological studies reveal that children born with a solitary functioning kidney (SFK) have a greater predisposition to develop renal insufficiency and hypertension in early adulthood. A congenital SFK is present in patients with unilateral renal agenesis or unilateral multicystic kidney dysplasia, leading to both structural and functional adaptations in the remaining kidney, which act to mitigate the reductions in glomerular filtration rate and sodium excretion that would otherwise ensue. To understand the mechanisms underlying the early development of renal insufficiency in children born with a SFK, we established a model of fetal uninephrectomy (uni-x) in sheep, a species that similar to humans complete nephrogenesis before birth. This model results in a 30% reduction in nephron number rather than 50%, due to compensatory nephrogenesis in the remaining kidney. Similar to children with a congenital SFK, uni-x sheep demonstrate a progressive increase in arterial pressure and a loss of renal function with aging. This review summarizes the compensatory changes in renal hemodynamics and tubular sodium handling that drive impairments in renal function and highlights the existence of sex differences in the functional adaptations following the loss of a kidney during fetal life.

Lysine-specific demethylase-1 modifies the age effect on blood pressure sensitivity to dietary salt intake

How interactions of an individual's genetic background and environmental factors, such as dietary salt intake, result in age-associated blood pressure elevation is largely unknown. Lysine-specific demethylase-1 (LSD1) is a histone demethylase that mediates epigenetic regulation and modification of gene transcription. We have shown previously that hypertensive African-American minor allele carriers of the LSD1 single nucleotide polymorphism (rs587168) display blood pressure salt sensitivity. Our goal was to further examine the effects of LSD1 genotype variants on interactions between dietary salt intake, age, and blood pressure. We found that LSD1 single nucleotide polymorphism (rs7548692) predisposes to increasing salt sensitivity during aging in normotensive Caucasian subjects. Using a LSD1 heterozygous knockout mouse model, we compared blood pressure values on low (0.02 % Na(+)) vs. high (1.6 % Na(+)) salt intake. Our results demonstrate significantly increased blood pressure salt sensitivity in LSD1-deficient compared to wild-type animals with age, confirming our findings of salt sensitivity in humans. Elevated blood pressure in LSD1(+/-) mice is associated with total plasma volume expansion and altered renal Na(+) excretion. In summary, our human and animal studies demonstrate that LSD1 is a genetic factor that interacts with dietary salt intake modifying age-associated blood pressure increases and salt sensitivity through alteration of renal Na(+) handling.

Blunted sodium excretion in response to a saline load in 5 year old female sheep following fetal uninephrectomy

Previously, we have shown that fetal uninephrectomy (uni-x) causes hypertension in female sheep by 2 years of age. Whilst the hypertension was not exacerbated by 5 years of age, these uni-x sheep had greater reductions in renal blood flow (RBF). To further explore these early indications of a decline in renal function, we investigated the renal response to a saline load (25 ml/kg/40 min) in 5-year old female uni-x and sham sheep. Basal mean arterial pressure was ∼15 mmHg greater (P(Group)<0.001), and sodium excretion (∼50%), glomerular filtration rate (∼30%, GFR) and RBF (∼40%) were all significantly lower (P(Group)<0.01) in uni-x compared to sham animals. In response to saline loading, sodium excretion increased significantly in both groups (P(Time)<0.001), however this response was blunted in uni-x sheep (P(GroupxTime)<0.01). This was accompanied with an attenuated increase in GFR and fractional sodium excretion (both P(GroupxTime)<0.05), and reduced activation of the renin-angiotensin system (both P<0.05), as compared to the sham group. The reduction in sodium excretion was associated with up-regulations in the renal gene expression of NHE3 and Na(+)/K(+) ATPase α and β subunits in the kidney cortex of the uni-x compared to the sham animals (P<0.05). Notably, neither group completely excreted the saline load within the recovery period, but the uni-x retained a higher percentage of the total volume (uni-x: 48±7%; sham: 22±9%, P<0.05). In conclusion, a reduced ability to efficiently regulate extracellular fluid homeostasis is evident in female sheep at 5 years of age, which was exacerbated in animals born with a congenital nephron deficit. Whilst there was no overt exacerbation of hypertension and renal insufficiency with age in the uni-x sheep, these animals may be more vulnerable to secondary renal insults.

Nonmodulation as the mechanism for salt sensitivity of blood pressure in individuals with hypertension and type 2 diabetes mellitus

CONTEXT

It is assumed that in individuals with type 2 diabetes mellitus (T2DM), blood pressure sensitivity to salt intake and the frequency of a low renin state are both increased compared with the nondiabetic population. However, studies supporting these assumptions may have been confounded by participant inclusion criteria, and study results may reflect target organ damage.

OBJECTIVE

The objective of this study was to examine in a cohort of T2DM 1) the frequency of salt sensitivity of blood pressure and 2) whether alterations of the renin-angiotensin-aldosterone system (RAAS) contribute to salt sensitivity in this population.

DESIGN, PATIENTS, AND METHODS

Within participants of the HyperPATH cohort, four groups were analyzed: 1) T2DM with hypertension (HTN), n=51; 2) T2DM without HTN, n=30; 3) HTN only, n=451; and 4) normotensive, n=209. Phenotype studies were conducted after participants completed two dietary phases: liberal sodium (200 mmol/d) and low sodium (10 mmol/d) for 7 d each. Participants were admitted overnight to a clinical research center after each diet, and supine measurements of the RAAS before and after a 60-min angiotensin II infusion (3 ng/kg·min) were obtained.

RESULTS

Multivariate regression analysis demonstrated that T2DM status (all individuals with T2DM vs. individuals without T2DM) was not associated with the change in mean arterial pressure between the low and liberal sodium diets after accounting for age, gender, body mass index, race, and baseline blood pressure (T2DM status, P=0.5). Furthermore, two intermediate phenotypes of altered RAAS, low renin, and nonmodulation (NMOD), were associated with salt-sensitive blood pressure but occurred at different frequencies in the T2DM-HTN and HTN groups (low renin, 12% T2DM-HTN vs. 29% HTN; NMOD, 41% T2DM-HTN vs. 27% HTN; P=0.01).

CONCLUSION

The frequency of NMOD in participants with T2DM was significantly higher compared with HTN, suggesting that the salt sensitivity often seen in T2DM is driven by NMOD.

Oxidative stress alters renal D1 and AT1 receptor functions and increases blood pressure in old rats

Aging is associated with an increase in oxidative stress and blood pressure (BP). Renal dopamine D1 (D1R) and angiotensin II AT1 (AT1R) receptors maintain sodium homeostasis and BP. We hypothesized that age-associated increase in oxidative stress causes altered D1R and AT1R functions and high BP in aging. To test this, adult (3 mo) and old (21 mo) Fischer 344 × Brown Norway F1 rats were supplemented without/with antioxidant tempol followed by determining oxidative stress markers (urinary antioxidant capacity, proximal tubular NADPH-gp91phox, and plasma 8-isoprostane), D1R and AT1R functions, and BP. The D1R and AT1R functions were determined by measuring diuretic and natriuretic responses to D1R agonist (SKF-38393; 1 μg·kg(-1)·min(-1) iv) and AT1R antagonist (candesartan; 10 μg/kg iv), respectively. We found that the total urinary antioxidant capacity was lower in old rats, which increased with tempol treatment. In addition, tempol decreased the elevated NADPH-gp91phox and 8-isoprostane levels in old rats. Systolic, diastolic, and mean arterial BPs were higher in old rats and were reduced by tempol. Although SKF-38393 produced diuresis in both adult and old rats, urinary sodium excretion (UNaV) increased only in adult rats. While candesartan increased diuresis and UNaV in adult and old rats, the magnitude of response was greater in old rats. Tempol treatment in old rats reduced candesartan-induced increase in diuresis and UNaV. Our results demonstrate that diminished renal D1R and exaggerated AT1R functions are associated with high BP in old rats. Furthermore, oxidative stress may cause altered renal D1R and AT1R functions and high BP in old rats.

Reduced nephron endowment due to fetal uninephrectomy impairs renal sodium handling in male sheep

Reduced nephron endowment is associated with development of renal and cardiovascular disease. We hypothesized this may be attributable to impaired sodium homoeostasis by the remaining nephrons. The present study investigated whether a nephron deficit, induced by fetal uninephrectomy at 100 days gestation (term=150 days), resulted in (i) altered renal sodium handling both under basal conditions and in response to an acute 0.9% saline load (50 ml.kg-1 of body weight.30 min-1); (ii) hypertension and (iii) altered expression of renal channels/transporters in male sheep at 6 months of age. Uninephrectomized animals had significantly elevated arterial pressure (90.1+/-1.6 compared with 77.8+/-2.9 mmHg; P<0.001), while glomerular filtration rate and renal blood flow (per g of kidney weight) were 30% lower than that of the sham animals. Total kidney weight was similar between the groups. Renal gene expression of apical NHE3 (type 3 Na+/H+ exchanger), ENaC (epithelium Na+ channel) beta and gamma subunits and basolateral Na+/K+ ATPase beta and gamma subunits were significantly elevated in uninephrectomized animals, while ENaC alpha subunit expression was reduced. Urine flow rate and sodium excretion increased in both groups in response to salt loading, but this increase in sodium excretion was delayed by approximately 90 min in the uninephrectomized animals, while total sodium output was 12% in excess of the infused load (P<0.05). In conclusion, the present study shows that animals with a congenital nephron deficit have alterations in tubular sodium channels/transporters and cannot rapidly correct for variations in sodium intake probably contributing to the development of hypertension. This suggests that people born with a nephron deficit should be monitored for early signs of renal and cardiovascular disease.

Renal response to angiotensin II is blunted in sodium-sensitive normotensive men

BACKGROUND

In hypertension, sodium sensitivity (SS) of blood pressure is associated with renal hemodynamic abnormalities related to increased activity of the renal renin-angiotensin aldosterone system (RAAS). The renal mechanisms of SS in normotensives are unknown. Therefore, we studied whether SS is related to renal hemodynamics and renal responsiveness to angiotensin II (AngII) in young healthy adults.

METHODS

Blood pressure (mean arterial pressure (MAP)) and renal function were measured in 34 healthy men after 1-week low-sodium diet (LS; 50 mmol Na(+)/24 h), 1-week high-sodium diet (HS; 200 mmol Na(+)/24h), and 1-week HS-ACEi (enalapril 20 mg/day). The responses of effective renal plasma flow (ERPF; (131)I-Hippuran clearance) to graded infusion of AngII were assessed during each condition.

RESULTS

The sodium-induced change in MAP ranged from -7 to +14 mm Hg. SS (a sodium-induced increase in MAP >3 mm Hg) was present in 13 subjects. ERPF was lower in SS subjects during LS and during HS-ACEi. The AngII-induced decrease in ERPF was blunted in SS on LS (-25 +/- 6 vs. -29 +/- 7% in sodium-resistant (SR) subjects, P < 0.05) and on HS (-30 +/- 5 vs. -35 +/- 6%, P < 0.05). The blunting was corrected by angiotensin-converting enzyme inhibitors (ACEi) (-36 +/- 6 vs. -37 +/- 7%).

CONCLUSION

SS normotensive subjects have a blunted renal response to exogenous AngII. This is ameliorated by ACEi, supporting a role for inappropriately high intrarenal RAAS activity. As these findings cannot be attributed to subclinical renal hypertensive damage, high intrarenal RAAS activity and altered renal hemodynamics may be primary phenomena underlying SS.

The influence of dietary sodium on blood pressure

The goal of this essay is to examine the evidence relating salt intake to blood pressure in humans. Despite studies involving many thousands of subjects and patients performed in many hundreds of centers the issue remains controversial-indeed far more controversial than seems appropriate. There is little disagreement that in some animal models and in some patients with hypertension salt intake can exert a rather substantial influence. There is more controversy on the responsible mechanisms. The greatest controversy, by far, involves whether or not policy should involve a mandatory reduction in salt intake in all members of the community. The available evidence shows that the influence of salt intake is too inconsistent and generally too small to mandate policy decisions at the community level. At the level of the individual patient and that patient's physician, it is important to recognize that salt intake can make a substantial contribution to hypertension. That contribution is more likely if the patient is old rather than young, obese rather than lean, black rather than white, has diabetes mellitus with hypertension, or has evidence of renal injury. Unfortunately, tools for assessing the sodium and chloride intake in the individual and for assessing its contribution to BP in the individual are inadequate. On the bright side, prognosis is improved substantially by the array of antihypertensive drugs available today.

Dietary sodium intake modulates myocardial relaxation responsiveness to angiotensin II

Dietary sodium alters renovascular responsiveness to angiotensin II (Ang II) in normal subjects. Evidence supports a connection among dietary sodium, the rennin-angiotensin system, and myocardial function. The authors hypothesized that a similar relationship would exist in the heart, and that the pattern of responses would be qualitatively similar to the renal vasculature. Thirteen healthy volunteers (aged 38.6 +/- 4 years) entered a 2 week crossover design study (week 1, high sodium diet [HS] > 200 mmol Na/day; week 2, low sodium diet [LS], < 10 mmol Na/day) to investigate the influence of dietary sodium and Ang II on myocardial relaxation and renal blood flow (RBF). At the end of each study week, the authors assessed diastolic function (myocardial relaxation velocities [E'] using tissue Doppler imaging) and RBF (para-aminohippurate clearance) at baseline and after infusion of Ang II (3 ng/kg/min x 45 min). On HS diet, E' and RBF were higher than on LS diet (E' 14.0 +/- 1.2 vs 12.6 +/- 1.0 cm/s, P = 0.02; RBF 596 +/- 24 vs 563 +/- 26 mL/min, P = 0.02). Dietary sodium significantly modulated E' and RBF responsiveness to Ang II infusion in like manner. HS was associated with increased responsiveness compared with a blunted LS response (HS DeltaE' -1.4 +/- 0.4 cm/s vs LS DeltaE' -0.1 +/- 0.3 cm/s, P = 0.02; HS DeltaRBF -135.2 +/- 13.2 vs LS DeltaRBF -62.5 +/- 10.1 mL/min, P < 0.01). The authors describe for the first time that dietary sodium modulates myocardial relaxation and responsiveness to Ang II. It is important to consider dietary sodium intake when assessing diastolic function. Ang II may play a role in the interaction between dietary sodium and myocardial relaxation. Future research will investigate whether abnormalities in these mechanisms play a role in disorders of diastolic function.

Nonmodulation and essential hypertension

Nonmodulation is a process in which there is a disorder in angiotensin-dependent control of the renal circulation and adrenal aldosterone release. The abnormalities are associated with an inability to handle a sodium load and salt-sensitive hypertension. All of the features are corrected by angiotensin-converting enzyme inhibition. A striking family history of hypertension and concordance of responses to angiotensin II in sibling pairs have suggested a familial factor. Genes governing renin substrate (angiotensinogen) production showed gene polymorphisms in nonmodulators. As nonmodulation occurs in approximately 40% of patients with essential hypertension, clearly other genes must contribute.

Prevalence of primary hyperaldosteronism in mild to moderate hypertension without hypokalaemia

Screening for primary hyperaldosteronism (PHA) is often indicated in individuals with resistant hypertension or hypokalaemia. However, in the far larger subset of the hypertensive population who do not fit into these criteria, the evidence for screening is conflicting and dependent on the disease prevalence. The purpose of this study was to examine the prevalence of PHA in a large population with mild to moderate hypertension and without hypokalaemia using a carefully controlled study protocol including a normotensive control population. Hypertensive subjects underwent medication washout and both hypertensive and normotensive subjects placed on a high-sodium diet prior to biochemical and haemodynamic testing. Study specific cutoff values were based on results from the normotensive population studied under identical conditions. A screening test (serum aldosterone/PRA ratio [ARR]>25 with a serum aldosterone level >8 ng/dl) was followed by a confirmatory test (urine aldosterone excretion rate [AER] >17 microg/24 h) to demonstrate evidence of PHA. An elevated ARR with a concomitant elevated serum aldosterone was present in 26 (7.5%) individuals. Of these, 11 (3.2%) had an elevated AER, consistent with evidence of PHA. Individuals with PHA had higher blood pressure and lower serum potassium levels while on a high-sodium diet. Sodium restriction neutralized these differences between PHA and essential hypertensives. The prevalence of PHA in this mild to moderate hypertensive population without hypokalaemia is at most 3.2%, a rate that might lead to excessive false positives with random screening in comparable populations. Hyperaldosteronism, when present, is responsive to sodium restriction.

Failure of angiotensin II to suppress plasma renin activity in normotensive subjects with a positive family history of hypertension

The renin-angiotensin system is implicated in the pathophysiology of hypertension. Renin release is regulated by a number of factors, including circulating Ang II (angiotensin II), the so-called short feedback loop. The aim of the present study was to investigate the responsiveness of circulating Ang II on PRA (plasma renin activity) in normotensive subjects with a PFH or NFH (positive or negative family history of hypertension respectively). PRA, renal haemodynamics and urinary sodium excretion were measured during infusion of Ang II without and with pretreatment with the AT1 (Ang II type 1) receptor blocker irbesartan. Normotensive men with a PFH (n=13) and NFH (n=10), with a mean age of 38 years, were given on different occasions intravenous Ang II infusions of 0.1, 0.5 and 1.0 ng.kg-1 of body weight.min-1 before and after pretreatment with 150 mg of irbesartan once a day for 5 consecutive days. RPF (renal plasma flow) and GFR (glomerular filtration rate) were also measured. Before Ang II infusion, the PFH and NFH groups did not differ with respect to BP (blood pressure), body mass index, PRA, RBF (renal blood flow) or urinary sodium. There was no difference in BP or renal haemodynamic response to the highest Ang II dose between the groups. PRA declined with the highest Ang II dose (P<0.01) in subjects with a NFH, but not in subjects with a PFH. After treatment with irbesartan when Ang II had no effect on BP in either group, Ang II also suppressed PRA in subjects with a PFH (P<0.01), and the difference between the groups at baseline was thus eliminated. In conclusion, these findings indicate that subjects with a PFH have a defective Ang II suppression of PRA, which is corrected by AT1 receptor blockade.

Genetic factors associated with volume-sensitive hypertension

Defining the genetic basis of essential hypertension is most informative when the blood pressure regulation is correlated with physiologic mechanisms, e.g., responses of the renin-angiotensin aldosterone system (RAAS) in hypertensive subjects. The aldosterone response to angiotensin II (Ang II) on a low salt diet is influenced by gender, plasma renin activity, and most significantly, familial resemblance, but only in males and in post-menopausal females. There is familial aggregation of low-renin hypertension, no association with candidate genes of the RAAS, but, a highly significant association with polymorphisms in the alpha-adducin gene. Finally, angiotensinogen (AGT) genotype effects renal and adrenal responses to Ang II in patients with hypertension. These results strongly suggest that in contrast to population-based studies that use hypertension as the phenotype, classifying patients by the variability in physiologic, mechanistic traits enhances the probability of identifying the genetic factors influencing a rise in blood pressure.

Controlled analysis of blood pressure sensitivity to sodium intake: interactions with hypertension type

OBJECTIVE

The contribution of salt intake to the pathogenesis of hypertension holds longstanding interest. Recent studies employed the sensitivity of blood pressure (BP) to salt intake as an intermediate phenotype. The validity of this approach relative to the homogeneity of sodium-sensitive hypertension was investigated while simultaneously controlling multiple putative factors.

METHODS

Blood pressure responses to shifts in salt intake were measured in 274 individuals with essential hypertension in steady-state sodium balance on high (200 mEq) and low (10 mEq) sodium intakes. Univariate and multivariate analyses predicted systolic and diastolic sodium sensitivity based on interactions among demographic factors (age, gender, race, body mass index) and hypertensive type [low-renin (LR), modulator (M), non-modulator (NM)].

RESULTS

The influence of hypertension type on systolic salt sensitivity (SSS) depended on gender (P = 0.03). In females, highest SSS was in LR (21, 14, 13 mmHg for LR, M, NM, P = 0.02), while in males highest SSS was in NM (11, 10, 16 mmHg for LR, M, NM, P = 0.07). Age predicted SSS without interacting with other factors, producing a 2.4 mmHg increase per decade (P = 0.02). Hypertension type affected diastolic salt sensitivity (DSS) (P = 0.002) without interacting with other factors. M had less DSS (6 mmHg) than LR (9 mmHg) and NM (11 mmHg) (P < 0.01).

CONCLUSIONS

For subjects in sodium balance, the distributions of SSS and DSS were unimodal and the mechanisms mediating SSS and DSS were different. Controlling for multiple demographic factors, at least two hypertensive types have largest BP responses to sodium intake, reducing the usefulness of blood pressure sensitivity to salt intake as an intermediate phenotype.

Renal perfusion in blacks: alterations caused by insuppressibility of intrarenal renin with salt

We have reported that an increased intrarenal renin-angiotensin system activity may be responsible for the reduction in renal plasma flow (RPF) in apparently healthy blacks in comparison to healthy whites during high salt balance. To ascertain whether these differences only exist in the high salt state, we performed the following study, concentrating on the manipulation of the renin system during low salt intake. We measured in 19 healthy blacks and 22 healthy whites para-aminohippurate and inulin clearances as an indication of RPF and glomerular filtration rate, respectively, on both high (200 mmol/d) and low (10 mmol/d) salt balance in random order. A subset of 11 blacks and 12 whites additionally received an angiotensin II infusion while in low salt balance (3 ng/kg per minute for 45 minutes) and captopril to assess differences in RPF response to a converting enzyme inhibitor. The 19 whites had significantly higher RPF when compared with blacks (P=0.033) when studied on high salt. However, during low salt balance, the RPFs were comparable in the 2 groups. Plasma renin activity was similar in the 2 groups on both diets. In the subset that received angiotensin II and captopril while in low salt balance, the renal vascular response was not different in whites and blacks. These data provide additional support for the concept that the intrarenal tissue renin system is more active in blacks than whites on a typical (high salt) diet and that the difference reflects primarily incomplete tissue renin suppression with an increase in salt intake. The mechanism involved may contribute to the increased susceptibility to renal injury in blacks.

Essential hypertension of Caribbean Hispanics: sodium, renin, and response to therapy

Little is known about essential hypertension in Hispanic Americans, despite the fact that they are the fastest-growing minority in the United States and have a disproportionate degree of hypertensive target organ damage. The authors studied 89 Caribbean Hispanic hypertensive patients who participated in six double-blind, randomized trials of antihypertensive agents. Demographics, laboratory data, sodium excretion, plasma renin activity, and atrial natriuretic peptide were obtained after 3-4 weeks on placebo. Blood pressure responses to angiotensin-converting enzyme (ACE) inhibitors, beta blockers, calcium channel blockers, hydrochlorothiazide (HCTZ), and fixed combinations of ACE inhibitors and HCTZ, were compared to the placebo values after 8-12 weeks of treatment. Patients had a multiple risk factor profile (obesity and diabetes) and a wide spectrum of blood pressure elevation, left ventricular hypertrophy, and hypertensive renal damage. Urine sodium excretion rates indicated inability to comply with salt restriction in 65% of patients. Plasma renin activity was lower than that of Hispanic normotensive controls, and 62% of patients had low-renin essential hypertension by renin profiling to sodium excretion. On analysis of variance, blood pressure reductions by calcium channel blockers, HCTZ, and ACE inhibitor/HCTZ combinations were significantly greater than that with placebo, while those of ACE inhibitors and beta blockers as monotherapy were not. The authors conclude that essential hypertension of Caribbean Hispanics is associated with multiple risk factors and is largely of the low-renin type. Responses to therapy are consistent with those observed in other populations with the low-renin phenotype and suggest salt-sensitivity of blood pressure in this population. Confirmation of the latter has implications for prevention and treatment of essential hypertension in Hispanics.

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

OBJECTIVE

An increased sensitivity to angiotensin II (Ang II) has been observed in patients with established hypertension. In the current study we tested whether young normotensive subjects with positive family history of arterial hypertension exhibit an increased sensitivity to Ang II, thereby potentially contributing to the pathogenesis of essential hypertension in these subjects.

METHODS AND DESIGN

Normotensive young men (25 +/- 2 years) with positive family history (PFH) (n = 28) and negative family history (NFH) (n = 60) of arterial hypertension were investigated to study aldosterone response, and systemic and renal haemodynamic changes (p-aminohippurate- and inulin-clearance) to Ang II infusion (0.5 and 3.0 ng/min per kg). In addition, aldosterone response to salt loading (5 g/day for 1 week) was analysed.

RESULTS

Ambulatory blood pressure (ABP) (mean: 84 +/- 4 versus 83 +/- 4 mmHg; NS), body mass index (23.5 +/- 2.5 versus 24.1 +/- 2.4 kg/m(2); NS), and urinary sodium excretion (191 +/- 55 versus 170 +/- 73 mmol/24 h; NS) did not differ between PFH and NFH at baseline. Changes in BP, urinary sodium and potassium excretion were similar between PFH and NFH in response to salt loading. However, salt loading did not result in an adequate suppression of aldosterone in PFH compared with NFH (8 +/- 62 versus -32 +/- 39 pg/ml; P < 0.001). Baseline values and changes in mean arterial BP (NFH: +13.4 +/- 7.6; PFH: +14.4 +/- 5.3 mmHg; NS), renal plasma flow (NFH: - 113 +/- 68; PFH: - 122 +/- 64 ml/min; NS) and glomerular filtration rate (NFH: +5.0 +/- 5.3; PFH: +4.2 +/- 8.3 ml/min; NS) in response to Ang II (3.0 ng/min per kg) were similar between the two groups. In contrast, the increases in serum aldosterone (PFH: 63.6 +/- 70.1 versus NFH: 37.7 +/- 46.8 pg/ml; P < 0.05) and urinary potassium excretion (PFH: 0.05 +/- 0.1 versus NFH: -0.01 +/- 0.07 mmol/min; P < 0.05) 30 min after stopping Ang II infusion were more pronounced and prolonged in PFH than in NFH.

CONCLUSIONS

Our findings suggest that young normotensive subjects with parental history of arterial hypertension are characterized by an inadequate suppression of aldosterone production in response to salt loading and an exaggerated and prolonged hyper-responsiveness of aldosterone secretion in response to Ang II. This might contribute to the increased risk for the development of essential hypertension in subjects with positive family history of arterial hypertension.

Angiotensinogen gene core promoter variants and non-modulating hypertension

Non-modulation has been suggested as a possible intermediate phenotype defining a subgroup of genetic hypertension. The trait is characterized by an attenuated response of renal blood flow and/or aldosterone to angiotensin (Ang) II. We tested the hypothesis that functional polymorphisms of the core promoter of the angiotensinogen gene are associated with non-modulation. Fifty-six young, white, male, untreated hypertensive patients and 65 age-matched normotensive volunteers were genotyped for 3 known functional variants of the angiotensinogen core promoter. All subjects were infused with 2 doses (0.5 and 3 ng/kg per minute) of Ang II while they were on a high sodium diet (250 mmol/d). The blood pressure, renal plasma flow, and aldosterone responses to Ang II were not affected by the -6 G/A polymorphism. The -20 A/C variant had no significant effects on the blood pressure or renal hemodynamic response to Ang II. However, the aldosterone response to both doses of Ang II was significantly decreased in -20 C allele carriers compared with -20 AA homozygotes in a multivariate analysis. The -18 T allele was not detected in our population, and there was a linkage dysequilibrium between -20 C and -6 A: -20 C almost exclusively occurred on the -6 A allele. Haplotype analysis indicated that the -20 C/-6 A haplotype but not the -20 A/-6 A haplotype was associated with a decreased aldosterone response to Ang II. We conclude that the -20 C variant or the -20 C/-6 A haplotype of the angiotensinogen core promoter is associated with a blunted aldosterone response to Ang II and may thus contribute to the non-modulating phenotype.

Salt sensitivity in genetically hypertensive rats of the Lyon strain

BACKGROUND

Genetically hypertensive (LH) rats of the Lyon strain exhibit a blunted pressure-natriuresis function when compared, in acute conditions, with their normotensive (LN) and low blood pressure (LL) controls. The present work was aimed to determine whether LH rats were salt sensitive in chronic conditions. In addition, a protocol was developed to determine the renal function curve in freely moving rats.

METHODS

Fourteen-week-old rats either untreated or orally treated since weaning with perindopril (3 mg/kg/24 h), an angiotensin-converting enzyme inhibitor, or with valsartan (15 mg/kg/24 h), an angiotensin II subtype 1 receptor antagonist, so as to eliminate the influence of endogenous changes in angiotensin formation were used. Blood pressure (BP) and urinary sodium excretion were measured before, during an oral salt load (2% NaCl in drinking water), and during a two-week aldosterone infusion (50 microg/kg/24 h subcutaneously).

RESULTS

NaCl induced a greater BP increase in untreated LH rats than in LN and LL controls. Perindopril normalized the BP of LH rats but not its elevation during a salt load. Aldosterone slightly increased BP in LH and LL rats either untreated or treated with valsartan. Finally, the combination of telemetric BP measurement with 24-hour urine collection when salt was added to drinking water allowed accurate determination of the slope of the chronic renal function curve in freely moving rats.

CONCLUSION

The present work demonstrates that LH rats are salt sensitive. This characteristic manifests despite the lack of an active renin-angiotensin system and is not explained by a hypersensitivity to aldosterone.

Steroid metabolism in metabolic syndrome X

Preceding chapters in this volume describe relatively rare conditions associated with qualitative rather than quantitative changes in enzymes involved in steroid synthesis and metabolism. In this chapter, several examples show how more subtle variations in activities of the same enzymes may be important in the pathophysiology of common diseases of complex aetiology. This chapter reviews evidence for deranged steroid metabolism in patients with the 'insulin resistance syndrome'. In summary, patients with essential hypertension may have subtle 11beta-hydroxylase or 11beta-hydroxysteroid dehydrogenase type 2 deficiency resulting in mild mineralocorticoid excess. Patients with obesity, and/or associated hirsutism or hyperglycaemia, have evidence of altered peripheral metabolism of androgens (increased 5alpha-reductase) and glucocorticoids (altered 11beta-hydroxysteroid dehydrogenase type 1, resulting in enhanced cortisol levels in adipose tissue). Some of these changes in steroid metabolism lend themselves to therapeutic manipulation which may provide novel strategies to reduce cardiovascular risk.

Sodium sensitivity related to albuminuria appearing before hypertension in type 2 diabetic patients

OBJECTIVE

To find whether sodium sensitivity of blood pressure appears before hypertension and whether the sensitivity is related to diabetic nephropathy, we examined type 2 diabetic patients with normal levels of serum creatinine.

RESEARCH DESIGN AND METHODS

A total of 32 patients were divided into three age-matched groups: 11 patients had normoalbuminuria, 12 had microalbuminuria, and 9 had macroalbuminuria. Patients stayed on a diet with ordinary sodium levels for 1 week and a sodium-restricted diet for 1 week, in random order. Urinary excretion of sodium and albumin and systemic blood pressure were measured daily. A pressure-natriuresis curve was drawn by linkage of the two datum points obtained in the steady state during the different diets. We calculated the sodium sensitivity index as the reciprocal of the slope of this curve.

RESULTS

The median sodium sensitivity index and the mean blood pressure were higher in micro- and macroalbuminuric patients than in normoalbuminuric patients. Eighteen patients were without hypertension (<140/90 mmHg); of these, 10 had blood pressure readings <130/85 mmHg with ordinary sodium levels. Urinary albumin was correlated with the index but not with blood pressure. For these 10 patients, the index in those with albuminuria was higher than in those with normoalbuminuria. In such patients with albuminuria, sodium restriction decreased albuminuria and blood pressure.

CONCLUSIONS

In type 2 diabetic patients with albuminuria but normal levels of serum creatinine, sodium sensitivity of blood pressure appears before hypertension and is related to albuminuria; sodium restriction is one treatment for diabetic nephropath, even without hypertension.

Enhanced antinatriuresis in response to angiotensin II in essential hypertension

Angiotensin II regulates sodium homeostasis by modulating aldosterone secretion, renal vascular response, and tubular sodium reabsorption. We hypothesized that the antinatriuretic response to angiotensin II is enhanced in human essential hypertension. We therefore studied 48 white men with essential hypertension (defined by ambulatory blood pressure measurement) and 72 normotensive white control persons, and measured mean arterial pressure, sodium excretion, renal plasma flow, glomerular filtration rate, and aldosterone secretion in response to angiotensin II infusion (0.5 and 3.0 ng/kg/min). Hypertensive subjects exhibited a greater increase of mean arterial pressure (16.7+/-8.2 mm Hg v 13.4+/-7.1 mm Hg in normotensives, P < .05) and a greater decrease of renal plasma flow (-151.5+/-73.9 mL/ min v -112.6+/-68.0 mL/min in controls, P < .01) when 3.0 ng/kg/min angiotensin II was infused. The increase of glomerular filtration rate and serum aldosterone concentration was similar in both groups. Sodium excretion in response to 3.0 ng/kg/min angiotensin II was diminished in both groups (P < .01). However, the decrease in sodium excretion was more pronounced in hypertensives than in normotensives (-0.18+/-0.2 mmol/min v -0.09+/-0.2 mmol/min, P < .05), even if baseline mean arterial pressure and body mass index were taken into account (P < .05). We conclude that increased sodium retention in response to angiotensin II exists in subjects with essential hypertension, which is unrelated to changes in glomerular filtration rate and aldosterone concentration. Our data suggest a hyperresponsiveness to angiotensin II in essential hypertension that could lead to increased sodium retention.

Adrenocortical responses to psychological stress and risk for hypertension

Excessive and prolonged stress-induced cortisol changes may contribute to or be a marker of essential hypertension. Cortisol is a central component of the stress response, and it interacts with sympathetic and renal mechanisms contributing to increased blood pressure (BP). Although research in individuals with already established hypertension failed to show consistent abnormalities in adrenocortical output, cortisol responses to psychological stress are greater and more persistent in persons at high risk for hypertension relative to low-risk normotensives. Considering the heterogeneous and multifactorial polygenic nature of hypertension and the fact that cortisol affects several BP related processes, and regulates expression of genes involved in BP, it is possible that this hormone is involved in at least a sub-type of hypertension. Recent studies evaluating cortisol tissue sensitivity, cortisol production and cortisol metabolic rate in hypertension-prone persons support the possibility that cortisol may serve as an intermediate phenotype of hypertension. In this review, we discuss components of the stress responses, factors influencing the adrenocortical response, adrenocortical activity in hypertension, and we propose pathways that mediate effects of stress-induced cortisol on BP.

Effect of ACE inhibition on pressor, renal vascular, and adrenal responses to infusion of angiotensin I in normal subjects eating a low-salt diet

To examine the influence of angiotensin-converting enzyme (ACE) on pressor, renal vascular, and adrenal responses during angiotensin I (Ang I) infusion, we studied 10 normotensive, healthy men. Each was in balance with a 10-mEq sodium, 100-mEq potassium intake and was studied before and during ACE inhibition with enalapril. Ang I (3, 10, and 30 ng/kg/min) was infused in each subject. Then ACE inhibition was instituted with enalapril for 3 days, which induced the anticipated fall in blood pressure, plasma Ang II, and aldosterone concentration, and rise in renal plasma flow. During ACE inhibition only the 30-ng/kg/min Ang I dose raised plasma Ang II levels. There was a spectrum, however, in the end-organ response to Ang I during ACE inhibition. Responses of plasma aldosterone concentration and blood pressure were in excellent accord with the reduction in Ang II formation. On the other hand, responses of the renal blood supply were substantially less inhibited than anticipated. Under the conditions of this study, ACE inhibition led to nonuniform changes in the response to exogenous Ang I, suggesting intrarenal conversion of Ang I to Ang II.

Aldosterone stimulation by angiotensin II : influence of gender, plasma renin, and familial resemblance

The aldosterone response to infused angiotensin II (Ang II) in patients receiving a low-salt diet has been described as an important phenotype for genetic studies on human hypertension. The objectives of the present study were to determine the parameters that influence this intermediate phenotype as a quantitative trait and to assess the importance of its familial resemblance in hypertensive sibling pairs. Two hundred one white hypertensive subjects (95 families: 84 pairs and 11 trios) were selected in 3 centers. The patients followed the same protocol, which included a 4-week withdrawal period of antihypertensive therapy, a 1-week period on a low-salt diet, and a 30-minute infusion of Ang II. The increase in the aldosterone level was greater in women than in men (29.1+/-16.2 versus 18.2+/-9.6 ng/dL, P<0.0001). A strong relationship was found with age (r=-0.54, P<10(-4)) and plasma renin activity (r=0.32, P<10(-4)) in women but not in men. Weak correlations of the aldosterone response to Ang II were observed for the whole set of sibling pairs (r=0.11, NS). Conversely, strong sibling correlations were found among brother-brother pairs (r=0.40, n=36) and among sister-sister pairs as soon as age or menopausal status was considered. Similar results were obtained when the Ang I-aldosterone response was analyzed as a qualitative trait (kappa=0. 35, P<0.008 in brother-brother pairs). We conclude that age, gender, and plasma renin are strong determinants of the aldosterone response to Ang II, with strong sibling correlations in men and postmenopausal women. These relationships will have to be considered in future linkage and association studies.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Relation between the renin-angiotensin-aldosterone system and left ventricular structure and function in young normotensive and mildly hypertensive subjects

BACKGROUND

High angiotensin II levels in relation to the corresponding urinary sodium excretion have been found to modulate left ventricular (LV) structure in middle-aged hypertensive patients. To analyze whether such a relation between the renin-angiotensin-aldosterone system and left ventricular structure is already present in young individuals, we examined the changes of angiotensin II and aldosterone in response to increased salt intake and their relations to LV structure and function.

METHODS

In 119 young (aged 26 +/- 3 years) patients with normal or mildly elevated blood pressure, we determined LV structure and function (2-dimensional guided M-mode echocardiography and pulse wave Doppler sonography) and 24-hour ambulatory blood pressure (SpaceLabs 90207). Dietary sodium intake as estimated by 24-hour urinary sodium excretion, plasma renin activity, angiotensin II, and aldosterone concentrations were measured first on a normal diet and second at high salt intake to determine the extent of the resulting suppression of the renin-angiotensin-aldosterone system.

RESULTS

Body mass index (r = 0.43, P <.001) and both systolic (r = 0.24, P <. 01) and diastolic (r = 0.19, P <.05) 24-hour ambulatory blood pressure correlated with LV mass. No straightforward relation was found between LV structure and baseline angiotensin II or aldosterone concentration. The increase of sodium excretion at high salt intake was related to a physiologically expected decrease of angiotensin II and aldosterone levels in normotensive (r = -0.36, P <.01 and r = -0.32; P =.016, respectively) but not in hypertensive patients. Changes in angiotensin II or aldosterone concentration were not related to LV structure in either hypertensive or normotensive young individuals. However, changes in aldosterone secretion correlated with diastolic filling parameters in hypertensive patients (velocity-time integrals of the A over E wave: r = 0.32, P =.03; atrial contribution of LV filling: r = 0.33, P =. 025) but not in normotensive individuals.

CONCLUSION

In contrast to middle-aged hypertensive patients, neither angiotensin II, aldosterone, nor their suppression in response to high salt intake were related to LV structure in young hypertensive patients. However, inadequate suppression of aldosterone after salt intake was associated with diastolic filling abnormalities in our young hypertensive patients, which may represent early changes in hypertensive heart disease and precede potential structural alterations.

Impaired renal vascular response to a D1-like receptor agonist but not to an ACE inhibitor in conscious spontaneously hypertensive rats

The natriuretic response to a dopamine 1-like receptor agonist is blunted in spontaneously hypertensive rats (SHRs). Whether the renal vasodilator response to D1-like receptor stimulation in SHRs is defective also is unclear. To determine whether the renal hemodynamic response to a D1-like receptor is impaired in SHR, we examined the effect of a continuous infusion of the D1-like receptor agonist fenoldopam (2 microg/kg/min) on systemic and renal hemodynamics in conscious SHRs and Wistar-Kyoto (WKY) rats. As an active control, we used an equivalent antihypertensive dosage of captopril (10 mg/kg). Fenoldopam significantly increased effective renal plasma flow (ERPF) in WKY rats (+22 +/- 5%; p < 0.01), whereas this response was absent in SHRs (+7 +/- 3%; NS). Mean arterial pressure (MAP) was significantly reduced in SHRs (-11 +/- 2%; p < 0.001), demonstrating a systemic vasodilator response to fenoldopam in SHRs. The reduction in renal vascular resistance (RVR) was more pronounced in WKY rats (-24 +/- 2%) than in SHRs (-13 +/- 4%; p < 0.05). Captopril significantly increased ERPF in SHRs (+16 +/- 3%; p < 0.001), demonstrating a preserved renal vasodilatory capacity in SHRs. The blunting of the renal vasodilatory response to fenoldopam in SHRs is present during a high as well as a low sodium intake. In conscious SHRs, the renal vasodilatory response to a D1-like receptor agonist is impaired, whereas the blood pressure response is more pronounced. The preserved renal vasodilatory response to captopril indicates that the defective vasodilatory response in SHRs is functional rather than due to altered structural properties of the renal vascular bed.

The cellular ionic basis of hypertension and allied clinical conditions

Two central concepts of human hypertensive disease remain poorly understood: (1) elevated blood pressure as merely one component of an underlying systemic condition, characterized by multiple defects in diverse tissues (eg, "Syndrome X"), and (2) the heterogeneity of hypertension, in which different and even opposite clinical responses to different dietary and drug therapies are routinely observed among equally hypertensive subjects. To help explain these clinical phenomena, a unifying "ionic hypothesis" is proposed, in which steady-state elevations of cytosolic free calcium and suppressed intracellular free magnesium levels, characteristic features of all hypertension, concomitantly alter the function of many tissues. In blood vessels this causes vasoconstriction, arterial stiffness, and/or hypertension; in the heart, cardiac hypertrophy; in platelets, increased aggregation and thrombosis; in fat and skeletal muscle, insulin resistance; in pancreatic beta cells, other endocrine tissues, and sympathetic neurons, potentiated stimulus-secretion coupling resulting in hyperinsulinemia, increased sympathetic nerve activity, and so on. Furthermore, an analysis of cellular biochemical, dietary-nutrient, and hormonal factors that normally regulate steady-state levels of these intracellular ions suggests an ionic equivalent to Laragh's volume-vasoconstriction analysis of hypertension. This provides a cellular-based explanation for the heterogeneity of hypertension and a rational basis for individualizing dietary and drug recommendations among different hypertensive subjects.

Dietary salt reduction in hypertension--what is the evidence and why is it still controversial?

The link between sodium intake and hypertension remains controversial because of inconsistency between early epidemiologic studies, which showed a strong positive relationship between salt intake and blood pressure/incidence of hypertension, and more recent studies, which showed only modest decreases in blood pressure with sodium reduction, particularly in the normotensive population. In addition, there is clinical evidence that sodium is related to target organ damage such as left ventricular hypertrophy and renal disease. Although the evidence available linking sodium intake and blood pressure in the general population is weak, sodium reduction has been shown to be useful in hypertensive patients, particularly salt-sensitive patients. Whether dietary sodium reduction should be recommended for the general population remains questionable because of marginal benefit and the suggestion of possible deleterious effects on cardiovascular outcomes independent of blood pressure. This paper will review the definition and methods used in determining salt sensitivity, the evidence linking sodium intake and target organ damage, and modern studies of salt and blood pressure.

Hyper-responsiveness to angiotensin II is related to cardiac structural adaptation in hypertensive subjects

BACKGROUND

Angiotensin II has been found to be a growth stimulating factor for myocardial cells. In humans, angiotensin II infusion causes vasoconstriction in systemic and renal vasculature and leads to aldosterone secretion. Our hypothesis was that hyper-responsiveness to angiotensin II is related to left ventricular mass in human essential hypertension.

METHODS AND RESULTS

In 30 normotensive individuals and 30 subjects with mild essential hypertension (white men, mean age 26+/-3 years), the responsiveness to angiotensin II was assessed by measuring changes in mean arterial pressure, renal blood flow, glomerular filtration rate and aldosterone secretion in response to i.v. angiotensin II infusion (0.5 and 3.0 ng/kg per min). The provoked changes to angiotensin II infusion were similar in the normotensive and hypertensive group with the exception of an exaggerated increase in mean arterial pressure in hypertensives (14+/-5 versus 10+/-5 mm Hg, P<0.001 at 3.0 ng/kg per min angiotensin II). The increase in mean arterial pressure was correlated with left ventricular mass in hypertensive subjects (angiotensin II 0.5 ng/kg per min: r = 0.49, P<0.005; angiotensin II 3.0 ng/kg per min: r = 0.35, P<0.05); no such correlation was found in the normotensive group. After taking into account baseline mean arterial pressure and body mass index, the increase in mean arterial pressure to angiotensin II 0.5 ng/kg per min was still correlated with left ventricular mass (partial r = 0.50, P<0.01). Similarly, the change of glomerular filtration rate but not of renal blood flow in response to angiotensin II 0.5 ng/kg per min was correlated with left ventricular mass, (r = 0.42, P<0.02) in the hypertensive group but not in the normotensive one. This relationship remained significant even after taking baseline glomerular filtration rate, mean arterial pressure and body mass index into account (partial r = 0.43, P<0.05).

CONCLUSION

Hyper-responsiveness to angiotensin II is related to an increased left ventricular mass in hypertensive subjects independent of blood pressure.

NaCl-induced renal vasoconstriction in salt-sensitive African Americans: antipressor and hemodynamic effects of potassium bicarbonate

In 16 African Americans (blacks, 14 men, 2 women) with average admission mean arterial pressure (MAP, mm Hg) 99.9+/-3.5 (mean+/-SEM), we investigated whether NaCl-induced renal vasoconstriction attends salt sensitivity and, if so, whether supplemental KHCO3 ameliorates both conditions. Throughout a 3-week period under controlled metabolic conditions, all subjects ate diets containing 15 mmol NaCl and 30 mmol potassium (K+) (per 70 kg body wt [BW] per day). Throughout weeks 2 and 3, NaCl was loaded to 250 mmol/d; throughout week 3, dietary K+ was supplemented to 170 mmol/d (KHCO3). On the last day of each study week, we measured renal blood flow (RBF) and glomerular filtration rate (GFR) using renal clearances of PAH and inulin. Ten subjects were salt sensitive (SS) (DeltaMAP >+5%) and 6 salt resistant (SR). In NaCl-loaded SS but not SR subjects, RBF (mL/min/1.73 m2) decreased from 920+/-75 to 828+/-46 (P<0.05); filtration fraction (FF, %) increased from 19. 4+/- to 21.4 (P<0.001); and renal vascular resistance (RVR) (10(3)xmm Hg/[mL/min]) increased from 101+/-8 to 131+/-10 (P<0.001). In all subjects combined, DeltaMAP varied inversely with DeltaRBF (r =-0.57, P=0.02) and directly with DeltaRVR (r = 0.65, P=0.006) and DeltaFF (r = 0.59, P=0.03), but not with MAP before NaCl loading. When supplemental KHCO3 abolished the pressor effect of NaCl in SS subjects, RBF was unaffected but GFR and FF decreased. The results show that in marginally K+-deficient blacks (1) NaCl-induced renal vasoconstrictive dysfunction attends salt sensitivity; (2) the dysfunction varies in extent directly with the NaCl-induced increase in blood pressure (BP); and (3) is complexly affected by supplemented KHCO3, GFR and FF decreasing but RBF not changing. In blacks, NaCl-induced renal vasoconstriction may be a pathogenetic event in salt sensitivity.

Tubuloglomerular feedback: its physiological and pathophysiological significance

The mammalian nephron has a unique structure called juxtaglomerular apparatus (JGA); the primary function of the JGA includes tubuloglomerular feedback. Why is such a structure necessary? Analyses of available data strongly suggest that JGA has evolved to provide a fine tuning of the autoregulation of glomerular hemodynamics and high glomerular filtration rate in the face of very limited salt intake of our terrestrial environment, a function essential to allow a wide range of fluid and electrolyte intake with stable milieu interieur. Salt intake in excess is unique only to recent human cultures: salt intake is ordinarily less than 1 to 2 g per 60 kg of body weight in wildlife, including paleolithic humans. Any mutation or alteration of JGA function leading to renal salt conservation or maladaptive to high salt intake will not manifest in a low salt intake and thus would have been beneficial or inconsequential for survival in a natural environment, respectively. Thus, the mutation or alteration will be carried to subsequent generations. However, such altered function will result in essential hypertension or a maladaptation of JGA to high salt intake, which is a unique behavior of human civilizations of recent centuries. The kidney has not adapted to high salt intake through our evolution.

Salt sensitivity: concept and pathogenesis

Almost two decades ago, the existence of a subset of essential hypertensive patients, who were sensitive (according to the increase in blood pressure levels) to the intake of a diet with a high salt content, was described. These patients are characterized by an increase in blood pressure and in body weight when switched from a low to a high sodium intake. The increase in body weight is due to the incapacity of the kidneys to excrete the whole intake of sodium until renal perfusion pressure (mean blood pressure) attains a level that is able to restore pressure-natriuresis relationship to values that enable the kidney to excrete the salt ingested or administered intravenously. Salt sensitivity does not seem to depend on the existence of an intrinsic renal defect to handle sodium, but on the existence of subtle abnormalities in the regulation of the sympathetic nervous system, the renin-angiotensin system or endothelial function. It is also relevant that organ damage secondary to arterial hypertension, has been shown in animal models and in hypertensive humans sensitive to a high salt intake to be significantly higher when compared with that of salt-resistant animals or humans. Interestingly, in humans, salt sensitivity has been shown to correlate with microalbuminuria, an important predictor of cardiovascular morbidity and mortality, which correlates with most of the cardiovascular risk factors commonly associated with arterial hypertension. One of these factors is insulin resistance, that usually accompanies high blood pressure in overweight and obese hypertensives. Insulin resistance and hyperinsulinism are present in a significant percentage of hypertensive patients developing cardiovascular symptoms or death. For these reasons, therapy of arterial hypertension must be directed, not only to facilitate the lowering of BP level, but also, to halt the mechanisms underlying the increase in BP, when salt intake is increased. Furthermore, therapy must preferably improve the diminished insulin sensitivity present in salt-sensitive subjects that contribute independently to increased cardiovascular risk.

Antihypertensive efficacy of angiotensin converting enzyme inhibition and aspirin counteraction

OBJECTIVE

Blockade of bradykinin breakdown and enhancement of prostaglandin release probably participate in the antihypertensive activity of angiotensin converting enzyme (ACE) inhibitors. Cyclooxygenase blockers may attenuate the efficacy of ACE inhibitors by interfering with prostaglandin synthesis, and patients taking aspirin may not benefit from ACE inhibition. This study was designed to evaluate the incidence of the counteractive phenomenon and to define minimal aspirin dosage that causes an antagonistic effect.

METHODS

These were 26 patients with mild to moderate hypertension (group 1) and 26 patients with severe untreated primary hypertension (group 2). Enalapril (20 mg twice a day) was used as a single drug in group 1 and was added to the combination of long-acting nifedipine (30 mg/day) and atenolol (50 mg/day) in group 2. Aspirin was tested at doses of 100 and 300 mg/day, and an attenuation of more than 20% of the mean blood pressure decrease produced by enalapril was the criteria that defined antagonism.

RESULTS

The 100 mg dose was ineffective. However, 300 mg aspirin had an antagonistic effect in 57% of patients in group 1 and 50% of patients in group 2: mean arterial pressure was lowered by 63% and 91% less, respectively. Results were independent of the drug administration order. In "responders," aspirin significantly attenuated the renin rise associated with ACE inhibition.

CONCLUSIONS

These findings suggest that a number of ACE-inhibited patients are susceptible to 300 mg/day aspirin, regardless of hypertension severity. Antagonism may be mediated through prostaglandin inhibition according to predominance, in an individual patient, of prostaglandin activation (also as a renin secretory stimulus) or angiotensin blockade by enalapril.