Angiotensin II and sympathetic activity in sodium-restricted essential hypertension

Association of Obesity, Sarcopenia, and Sarcopenic Obesity With Hypertension in Adults: A Cross-Sectional Study From Ravansar, Iran During 2014-2017

BACKGROUND AND AIMS

Hypertension may lead to disability and death by increasing the risk of cardiovascular disease, kidney failure, and dementia. This study aimed to determine the association between obesity, sarcopenia and sarcopenic obesity, and hypertension in adults resident in Ravansar, a city in the west of Iran.

METHODS

This cross-sectional study was conducted on 4,021 subjects from the baseline data of the Ravansar Non-Communicable Disease (RaNCD) cohort study, in the west region of Iran, from October 2014 up to February 2017. Body composition was categorized into obese, sarcopenia, sarcopenic obese, and normal based on measurements of muscle strength, skeletal muscle mass, and waist circumference. Univariate and multiple logistic regression models were used to examine the relationships, using the STATA 15 software.

RESULTS

The mean age of the participant was 47.9 years (SD: 8.4), the body mass index (BMI) was 26.84 kg/m² (SD: 4.44), and the prevalence of hypertension was 15.12%. The prevalence of obesity, sarcopenia, and sarcopenic obesity were 24.37, 22.01, and 6.91%, respectively. Body composition groups had significant differences in age, total calorie intake, BMI, skeletal muscle mass, and muscle strength (P-value ≤ 0.001). In crude model, the obese (OR = 2.64; 95% CI: 2.11-3.30), sarcopenic (OR = 2.45; 95% CI: 1.94-3.08), and sarcopenic obese (OR = 3.83; 95% CI: 2.81-5.22) groups had a higher odds of hypertension. However, in adjusted models, only the obese group had a higher likelihood of hypertension (OR = 2.18; 95% CI: 1.70-2.80).

CONCLUSION

This study showed that obesity was associated with hypertension, whereas sarcopenia and sarcopenic obesity had no significant relationship with hypertension.

Mechanisms of decreased tubular flow-induced nitric oxide in Dahl salt-sensitive rat thick ascending limbs

Dahl salt-sensitive (SS) rat kidneys produce less nitric oxide (NO) than those of salt-resistant (SR) rats. Thick ascending limb (TAL) NO synthase 3 (NOS3) is a major source of renal NO, and luminal flow enhances its activity. We hypothesized that flow-induced NO is reduced in TALs from SS rats primarily due to NOS uncoupling and diminished NOS3 expression rather than scavenging. Rats were fed normal-salt (NS) or high-salt (HS) diets. We measured flow-induced NO and superoxide in perfused TALs and performed Western blots of renal outer medullas. For rats on NS, flow-induced NO was 35 ± 6 arbitrary units (AU)/min in TALs from SR rats but only 11 ± 2 AU/min in TALs from SS (P < 0.008). The superoxide scavenger tempol decreased the difference in flow-induced NO between strains by about 36% (P < 0.020). The NOS inhibitor N-nitro-l-arginine methyl ester (l-NAME) decreased flow-induced superoxide by 36 ± 8% in TALs from SS rats (P < 0.02) but had no effect in TALs from SR rats. NOS3 expression was not different between strains on NS. For rats on HS, the difference in flow-induced NO between strains was enhanced (SR rats: 44 ± 10 vs. SS: 9 ± 2 AU/min, P < 0.005). Tempol decreased the difference in flow-induced NO between strains by about 37% (P < 0.012). l-NAME did not significantly reduce flow-induced superoxide in either strain. HS increased NOS3 expression in TALs from SR rats but not in TALs from SS rats (P < 0.003). We conclude that 1) on NS, flow-induced NO is diminished in TALs from SS rats mainly due to NOS3 uncoupling such that it produces superoxide and 2) on HS, the difference is enhanced due to failure of TALs from SS rats to increase NOS3 expression.NEW & NOTEWORTHY The Dahl rat has been used extensively to study the causes and effects of salt-sensitive hypertension. Our study suggests that more complex processes other than simple scavenging of nitric oxide (NO) by superoxide lead to less NO production in thick ascending limbs of the Dahl salt-sensitive rat. The predominant mechanism involved depends on dietary salt. Impaired flow-induced NO production in thick ascending limbs most likely contributes to the Na+ retention associated with salt-sensitive hypertension.

Cardiovascular Risk in Patients with Prehypertension and the Metabolic Syndrome

Prehypertension (pHTN) and metabolic syndrome (MetS) are both lifestyle diseases that are potentiated by increased adiposity, as both disease processes are closely related to weight. In the case of pHTN, increased adiposity causes dysregulation of the renin-angiotensin-aldosterone-system (RAAS) as well as adipokine- and leptin-associated increases in adrenergic tone. In MetS, excess weight potentiates hyperglycemia and insulin resistance which causes positive feedback into the RAAS system, activates an inflammatory cascade that potentiates atherosclerosis, and causes lipid dysregulation which together contribute to cardiovascular disease, especially coronary heart disease (CHD) and heart failure (HF). The relationship with all-cause mortality is not as clear-cut in part because of some protective effects associated with the obesity paradox in chronic diseases such as CHD and HF. However, in healthy populations, the absence of excess weight and its associated effects on prehypertension and MetS are associated with a longer absolute and disease-free lifespan.

Obesity and hypertension

The imbalance between energy intake and expenditure is the main cause of excessive overweight and obesity. Technically, obesity is defined as the abnormal accumulation of ≥20% of body fat, over the individual's ideal body weight. The latter constitutes the maximal healthful value for an individual that is calculated based chiefly on the height, age, build and degree of muscular development. However, obesity is diagnosed by measuring the weight in relation to the height of an individual, thereby determining or calculating the body mass index. The National Institutes of Health have defined 30 kg/m² as the limit over which an individual is qualified as obese. Accordingly, the prevalence of obesity in on the increase in children and adults worldwide, despite World Health Organization warnings. The growth of obesity and the scale of associated health issues induce serious consequences for individuals and governmental health systems. Excessive overweight remains among the most neglected public health issues worldwide, while obesity is associated with increasing risks of disability, illness and death. Cardiovascular diseases, the leading cause of mortality worldwide, particularly hypertension and diabetes, are the main illnesses associated with obesity. Nevertheless, the mechanisms underlying obesity-associated hypertension or other associated metabolic diseases remains to be adequately investigated. In the present review, we addressed the association between obesity and cardiovascular disease, particularly the biological mechanisms linking obesity and hypertension.

Blood pressure in Afghan male immigrants to Denmark

PURPOSE

Immigration from a Third-World society to a Western society can be associated with higher blood pressure and salt sensitivity. We therefore tested whether immigrants from Afghanistan to Denmark compared with non-immigrant Danes exhibit a (i) higher 24-h ambulatory blood pressure (24-h ABP) and (ii) blunted renin response to a change in salt intake.

METHODS

Twenty-four-hour ABP was measured in 40 men of Afghan (Afghans) and 40 men of Danish (Danes) origin. Each group was divided into young (20-30 years, n = 20) and middle aged (40-60 years, n = 20). A 3-day low (70 mmol per 24-h) and a 3-day high (250 mmol per 24-h) salt intake were in addition instituted in subgroups of the young groups (n = 18).

RESULTS

Young and middle-aged Afghans exhibited a lower 24-h mean arterial pressure (24-h MAP) than the same respective age groups of Danes (83 ± 1 versus 90 ± 1 mm Hg, P<0·05, and 89 ± 2 versus 100 ± 1 mm Hg, P<0·05). 24-h ABP did not change in any of the young groups during increased salt intake, whereas the Danes exhibited a greater decrease in plasma renin activity (PRA) (P<0·05). Plasma noradrenaline (PNA ) was significantly higher among the young Afghans.

CONCLUSIONS

Afghan immigrants to Denmark exhibit a lower 24-h ABP than Danes. In young Afghans, PRA is less sensitive to changes in salt intake, while PNA is higher and may reflect their lower systolic blood pressure and/or arterial pulse pressure. Whether these hormonal differences can explain the lower 24-h ABP in Afghans should be further explored.

Sympathetic regulation of vascular function in health and disease

The sympathetic nervous system (SNS) is known to play a pivotal role in short- and long-term regulation of different functions of the cardiovascular system. In the past decades increasing evidence demonstrated that sympathetic neural control is involved not only in the vasomotor control of small resistance arteries but also in modulation of large artery function. Sympathetic activity and vascular function, both of which are key factors in the development and prognosis of cardiovascular events and disease, are linked at several levels. Evidence from experimental studies indicates that the SNS is critically influenced, at the central and also at the peripheral level, by the most relevant factors regulating vascular function, such as nitric oxide (NO), reactive oxygen species (ROS), endothelin (ET), the renin-angiotensin system. Additionally, there is indirect evidence of a reciprocal relationship between endothelial function and activity of the SNS. A number of cardiovascular risk factors and diseases are characterized both by increased sympathetic outflow and decreased endothelial function. In healthy subjects, muscle sympathetic nerve activity (MSNA) appears to be related to surrogate markers of endothelial function, and an acute increase in sympathetic activity has been associated with a decrease in endothelial function in healthy subjects. However, direct evidence of a cause-effect relationship from human studies is scanty. In humans large artery stiffness has been associated with increased sympathetic discharge, both in healthy subjects and in renal transplant recipients. Peripheral sympathetic discharge is also able to modulate wave reflection. On the other hand, large artery stiffness can interfere with autonomic regulation by impairing carotid baroreflex sensitivity.

Mechanisms of obesity-induced hypertension

The relationship between obesity and hypertension is well established both in children and adults. The mechanisms through which obesity directly causes hypertension are still an area of research. Activation of the sympathetic nervous system has been considered to have an important function in the pathogenesis of obesity-related hypertension. The arterial-pressure control mechanism of diuresis and natriuresis, according to the principle of infinite feedback gain, seems to be shifted toward higher blood-pressure levels in obese individuals. During the early phases of obesity, primary sodium retention exists as a result of increase in renal tubular reabsorption. Extracellular-fluid volume is expanded and the kidney-fluid apparatus is resetted to a hypertensive level, consistent with a model of hypertension because of volume overload. Plasma renin activity, angiotensinogen, angiotensin II and aldosterone values display significant increase during obesity. Insulin resistance and inflammation may promote an altered profile of vascular function and consequently hypertension. Leptin and other neuropeptides are possible links between obesity and the development of hypertension. Obesity should be considered as a chronic medical condition, which is likely to require long-term treatment. Understanding of the mechanisms associated with obesity-related hypertension is essential for successful treatment strategies.

Salt, blood pressure and the renin-angiotensin system

Much evidence from epidemiological, migration, intervention, animal and genetic studies suggests that salt intake plays an important role in regulating blood pressure (BP). At the same time, many clinical trials have shown that reducing salt intake lowers BP. However, the magnitude of the fall in BP for a given reduction in salt intake varies with age, ethnic group and BP levels. This difference has been suggested to be related to the responsiveness of the renin-angiotensin system (RAS). However, the sympathetic nervous system, the kallikrein-kinin system, the nitric oxide system, and many eicosanoids may also play a role. In this article, we address the important role of the RAS in determining the fall in BP with salt reduction.

Relationship between the circulating and vascular renin-angiotensin system and the vasodilating effect of captopril in human hypertension

A vascular renin-angiotensin system (RAS) is present in the forearm vasculature of essential hypertensive patients and is closely related to the circulating renin profile. To test whether the haemodynamic effect of acute intrabrachial administration of captopril is related to the circulating and/or vascular RAS, 31 hypertensive patients were selected and divided into four groups according to their different circulating RAS profile (n = 7 hypertensive patients with primary aldosteronism and suppressed plasma renin activity; n = 7 low renin essential hypertensive patients; n = 8 normal renin essential hypertensive patients; n = 9 high renin renovascular hypertensive patients). The forearm net balance of active renin, plasma renin activity and angiotensin II, obtained by intrabrachial infusion of the beta-adrenergic receptor agonist isoproterenol (0.03, 0.1, 0.3 microg/100 ml/min) and calculated as the product of the venous-arterial plasma concentration gradient and forearm blood flow (FBF), was closely related to the circulating RAS. Captopril (0.25, 2.5, 25 microg/100 ml/min per 20 min each dose) unchanged basal FBF in the primary aldosteronism and low renin groups (FBF increase: from 3.9 +/- 0.4 to a maximum of 4.1 +/- 0.5 and from 3.8 +/- 0.3 to a maximum of 4.3 +/- 0.5 ml/100 ml/min, respectively), whereas it caused slight vasodilation in the normal renin group (from 3.9 +/- 0.3 to a maximum of 5.3 +/- 0.7 ml/100 ml/min), and pronounced vasodilation in the high renin group (from 4.0 +/- 0.4 to a maximum of 6.4 +/- 0.5 ml/100 ml/min). Captopril-induced vasodilation showed a significant direct correlation with the circulating and vascular RAS. The present data, while confirming the existence of a vascular RAS in the forearm of hypertensive patients indicate that the acute vasodilating effect of intrabrachial captopril is linked to a stimulated RAS, either circulating or vascular, supporting the evidence that, in acute conditions, ACE inhibitors exert their vasodilating effect through the RAS blockade.

Adenosine causes the release of active renin and angiotensin II in the coronary circulation of patients with essential hypertension

OBJECTIVES

The aim of the study was to evaluate whether adenosine infusion can induce production of active renin and angiotensin II in human coronary circulation.

BACKGROUND

Adenosine can activate angiotensin production in the forearm vessels of essential hypertensive patients.

METHODS

In six normotensive subjects and 12 essential hypertensive patients adenosine was infused into the left anterior descending coronary artery (1, 10, 100 and 1,000 microg/min x 5 min each) while active renin (radioimmunometric assay) and angiotensin II (radioimmunoassay after high performance liquid chromatography purification) were measured in venous (great cardiac vein) and coronary arterial blood samples. In five out of 12 hypertensive patients adenosine infusion and plasma samples were repeated during intracoronary angiotensin-converting enzyme inhibitor benazeprilat (25 microg/min) administration. Finally, in adjunctive hypertensive patients, the same procedure was applied during intracoronary sodium nitroprusside (n = 4) or acetylcholine (n = 4).

RESULTS

In hypertensive patients, but not in control subjects, despite a similar increment in coronary blood flow, a significant (p < 0.05) transient increase of venous active renin (from 10.7 +/- 1.4 [95% confidence interval 9.4 to 11.8] to a maximum of 13.8 +/- 2.1 [12.2 to 15.5] with a consequent drop to 10.9 +/- 1.8 [9.7 to 12.1] pg/ml), and angiotensin II (from 14.6 +/- 2.0 [12.7 to 16.5] to a maximum of 20.4 +/- 2.7 [18.7 to 22.2] with a consequent drop to 16.3 +/- 1.8 [13.9 to 18.7] pg/ml) was observed under adenosine infusion, whereas arterial values did not change. Calculated venous-arterial active renin and angiotensin II release showed a strong correlation (r = 0.78 and r = 0.71, respectively; p < 0.001) with circulating active renin. This adenosine-induced venous angiotensin II increase was significantly blunted by benazeprilat. Finally, both sodium nitroprusside and acetylcholine did not affect arterial and venous values of active renin and angiotensin II.

CONCLUSIONS

These data indicate that exogenous adenosine stimulates the release of active renin and angiotensin II in the coronary arteries of essential hypertensive patients, and suggest that this phenomenon is probably due to renin release from tissue stores of renally derived renin.

Regulation of peripheral vascular tone in patients with heart failure: contribution of angiotensin II

OBJECTIVE

To determine directly the contribution of angiotensin II to basal and sympathetically stimulated peripheral arteriolar tone in patients with heart failure.

DESIGN

Parallel group comparison.

SUBJECTS

Nine patients with New York Heart Association grade II-IV chronic heart failure, and age and sex matched controls.

INTERVENTIONS

Forearm plethysmography, lower body negative pressure, local intra-arterial administration of losartan, angiotensin II, and noradrenaline, and estimation of plasma hormone concentrations.

MAIN OUTCOME MEASURES

Forearm blood flow responses, plasma hormone concentrations.

RESULTS

Baseline blood pressure, heart rate, and forearm blood flow did not differ between patients and controls. In comparison with the non-infused forearm, losartan did not affect basal forearm blood flow (95% confidence interval -5.5% to +7.3%) or sympathetically stimulated vasoconstriction in controls. However, the mean (SEM) blood flow in patients increased by 13(5)% and 26(7)% in response to 30 and 90 micrograms/min of losartan respectively (p < 0.001). Lower body negative pressure caused a reduction in forearm blood flow of 20(5)% in controls (p = 0.008) and 13(5)% (p = 0.08) in patients (p = 0.007, controls v patients). Blood flow at 90 micrograms/min of losartan correlated with plasma angiotensin II concentration (r = 0.77; p = 0.03). Responses to angiotensin II and noradrenaline did not differ between patients and controls.

CONCLUSIONS

Losartan causes acute local peripheral arteriolar vasodilation in patients with heart failure but not in healthy control subjects. Endogenous angiotensin II directly contributes to basal peripheral arteriolar tone in patients with heart failure but does not augment sympathetically stimulated peripheral vascular tone.

Dietary sodium restriction impairs insulin sensitivity in noninsulin-dependent diabetes mellitus

Dietary sodium restriction has a variety of effects on metabolism, including activation of the renin-angiotensin system. Angiotensin II has complex metabolic and cardiovascular effects, and these may be relevant to the effects of both nonpharmacological and pharmacological interventions in noninsulin-dependent diabetes mellitus (NIDDM). We have assessed the effect of dietary sodium restriction on insulin sensitivity and endogenous glucose production in eight normotensive patients with diet-controlled NIDDM who underwent hyperinsulinemic clamp studies in a randomized, double-blind, placebo-controlled cross-over protocol after two 4-day periods on sodium replete (160 mmol/day) and sodium deplete (40 mmol/day) diets. Mean +/- SD 24-h urinary sodium was 197 +/- 76.0 mmol (replete) and 67 +/- 19.5 mmol (deplete), P = 0.03. Insulin sensitivity was 42.0 +/- 11.3 mumol/kg.min (replete) and 37.0 +/- 11.6 mumol/kg.min (deplete), P = 0.04 (a reduction of 12%). Blood pressure was 130 +/- 21/78 +/- 11 mmHg (replete) and 128 +/- 12/73 +/- 10 mmHg (deplete). Dietary sodium restriction may result in a decrease in peripheral insulin sensitivity in normotensive patients with NIDDM, possibly via an elevation in prevailing angiotensin II concentrations.