Renal sympathetic activity: A key modulator of pressure natriuresis in hypertension

Silent Effects of High Salt: Risks Beyond Hypertension and Body's Adaptation to High Salt

Hypertension is a major contributor to heart disease, renal failure, and stroke. High salt is one of the significant risk factors associated with the onset and persistence of hypertension. Experimental and observational studies have confirmed cardiovascular and non-cardiovascular detrimental effects associated with chronic intake of high salt. Because of convenience and present urban lifestyles, consumption of fast food has led to daily salt intake above the recommended level by the World Health Organization. This study provides an understanding of the body regulatory mechanisms that maintain sodium homeostasis under conditions of high salt intake, without health consequences, and how these mechanisms adapt to chronic high salt load, leading to adverse cardiovascular, renal, and non-cardiovascular outcomes. Recent research has identified several mechanisms through which high sodium intake contributes to hypertension. Of them, heightened renin-angiotensin-aldosterone and sympathetic activity associated with impaired pressure diuresis and natriuresis and decreased renal excretory response are reported. Additionally, there is the possibility of endothelial and nitric oxide dysfunction leading to vascular remodeling. These changes raise cardiac output and peripheral vascular resistance. Knowing how these collective mechanisms adapt to chronic intakes of high salt helps develop effective therapeutic policies to fight salt-induced hypertension.

Reactive oxygen species in hypertension

Hypertension is a leading risk factor for stroke, heart disease and chronic kidney disease. Multiple interacting factors and organ systems increase blood pressure and cause target-organ damage. Among the many molecular elements involved in the development of hypertension are reactive oxygen species (ROS), which influence cellular processes in systems that contribute to blood pressure elevation (such as the cardiovascular, renal, immune and central nervous systems, or the renin-angiotensin-aldosterone system). Dysregulated ROS production (oxidative stress) is a hallmark of hypertension in humans and experimental models. Of the many ROS-generating enzymes, NADPH oxidases are the most important in the development of hypertension. At the cellular level, ROS influence signalling pathways that define cell fate and function. Oxidative stress promotes aberrant redox signalling and cell injury, causing endothelial dysfunction, vascular damage, cardiovascular remodelling, inflammation and renal injury, which are all important in both the causes and consequences of hypertension. ROS scavengers reduce blood pressure in almost all experimental models of hypertension; however, clinical trials of antioxidants have yielded mixed results. In this Review, we highlight the latest advances in the understanding of the role and the clinical implications of ROS in hypertension. We focus on cellular sources of ROS, molecular mechanisms of oxidative stress and alterations in redox signalling in organ systems, and their contributions to hypertension.

Renal nerves in physiology, pathophysiology and interoception

Sympathetic efferent renal nerves have key roles in the regulation of kidney function and blood pressure. Increased renal sympathetic nerve activity is thought to contribute to hypertension by promoting renal sodium retention, renin release and renal vasoconstriction. This hypothesis led to the development of catheter-based renal denervation (RDN) for the treatment of hypertension. Two RDN devices that ablate both efferent and afferent renal nerves received FDA approval for this indication in 2023. However, in animal models, selective ablation of afferent renal nerves resulted in comparable anti-hypertensive effects to ablation of efferent and afferent renal nerves and was associated with a reduction in sympathetic nerve activity. Selective afferent RDN also improved kidney function in a chronic kidney disease model. Notably, the beneficial effects of RDN extend beyond hypertension and chronic kidney disease to other clinical conditions that are associated with elevated sympathetic nerve activity, including heart failure and arrhythmia. These findings suggest that the kidney is an interoceptive organ, as increased renal sensory nerve activity modulates sympathetic activity to other organs. Future studies are needed to translate this knowledge into novel therapies for the treatment of hypertension and other cardiorenal diseases.

Blood Pressure Stability and Plasma Aldosterone Reduction: The Effects of a Sodium and Bicarbonate-Rich Water - A Randomized Controlled Intervention Study

Objective: Hypertension is a recognized risk factor for cardiovascular disease (CVD), and dietary sodium intake has been linked to its development. However, mineral water high in bicarbonate and sodium does not appear to have adverse effects on blood pressure.This study examines the effects of consuming a mineral water high in bicarbonate and sodium (HBS) compared to a low bicarbonate and sodium (LBS) mineral water on blood pressure and related factors.Methods: A randomized controlled intervention was conducted with 94 healthy participants, consuming 1,500 - 2,000 mL daily of either mineral water high in bicarbonate and sodium (HBS water, n = 49) or low in bicarbonate and sodium (LBS water, n = 45). Blood pressure, anthropometrics, and urinary calcium and sodium excretion were assessed at baseline and after 28 days. 3-day food protocols were assessed to evaluate possible dietary changes.Results: Blood pressure changes did not differ between the groups. Both normotensive and hypertensive subjects showed similar changes in systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) in response to the different test waters. Serum aldosterone decreased significantly in both groups, with a greater reduction in the HBS group. Urinary calcium excretion significantly decreased (p = 0.002) and sodium excretion increased in the HBS group. Multiple linear regression analyses indicated no association between urinary sodium excretion and systolic blood pressure increase in the HBS group (B = 0.046, p = 0.170). Changes in urinary sodium excretion did not correlate with changes in serum aldosterone in the same group (r=-0.146, p = 0.350).Conclusions: The study revealed no significant differences in blood pressure changes between individuals consuming HBS water and LBS water. Notably, the additional sodium intake from the test water was effectively excreted.Trial registration: This trial was registered in the German Clinical Trials Register (DRKS00025341, https://drks.de/search/en).

Linear Correlation Between Mean Arterial Pressure and Urine Output in Critically Ill Patients

OBJECTIVE

Mean arterial pressure (MAP) plays a significant role in regulating tissue perfusion and urine output (UO). The optimal MAP target in critically ill patients remains a subject of debate. We aimed to explore the relationship between MAP and UO.

DESIGN

A retrospective observational study.

SETTING

A general ICU in a tertiary medical center.

PATIENTS

All critically ill patients admitted to the ICU for more than 10 hours.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

MAP values and hourly UO were collected in 5,207 patients. MAP levels were categorized into 10 groups of 5 mm Hg (from MAP < 60 mm Hg to MAP > 100 mg Hg), and 656,423 coupled hourly mean MAP and UO measurements were analyzed. Additionally, we compared the UO of individual patients in each MAP group with or without norepinephrine (NE) support or diuretics, as well as in patients with acute kidney injury (AKI).Hourly UO rose incrementally between MAP values of 65-100 mm Hg. Among 2,226 patients treated with NE infusion, mean UO was significantly lower in the MAP less than 60 mm Hg group (53.4 mL/hr; 95% CI, 49.3-57.5) compared with all other groups (p < 0.001), but no differences were found between groups of 75 less than or equal to MAP. Among 2500 patients with AKI, there was a linear increase in average UO from the MAP less than 60 mm Hg group (57.1 mL/hr; 95% CI, 54.2-60.0) to the group with MAP greater than or equal to 100 mm Hg (89.4 mL/hr; 95% CI, 85.7-93.1). When MAP was greater than or equal to 65 mm Hg, we observed a statistically significant trend of increased UO in periods without NE infusion.

CONCLUSIONS

Our analysis revealed a linear correlation between MAP and UO within the range of 65-100 mm Hg, also observed in the subgroup of patients treated with NE or diuretics and in those with AKI. These findings highlight the importance of tissue perfusion to the maintenance of diuresis and achieving adequate fluid balance in critically ill patients.

Epigenetics of hypertension as a risk factor for the development of coronary artery disease in type 2 diabetes mellitus

Hypertension, a multifaceted cardiovascular disorder influenced by genetic, epigenetic, and environmental factors, poses a significant risk for the development of coronary artery disease (CAD) in individuals with type 2 diabetes mellitus (T2DM). Epigenetic alterations, particularly in histone modifications, DNA methylation, and microRNAs, play a pivotal role in unraveling the complex molecular underpinnings of blood pressure regulation. This review emphasizes the crucial interplay between epigenetic attributes and hypertension, shedding light on the prominence of DNA methylation, both globally and at the gene-specific level, in essential hypertension. Additionally, histone modifications, including acetylation and methylation, emerge as essential epigenetic markers linked to hypertension. Furthermore, microRNAs exert regulatory influence on blood pressure homeostasis, targeting key genes within the aldosterone and renin-angiotensin pathways. Understanding the intricate crosstalk between genetics and epigenetics in hypertension is particularly pertinent in the context of its interaction with T2DM, where hypertension serves as a notable risk factor for the development of CAD. These findings not only contribute to the comprehensive elucidation of essential hypertension but also offer promising avenues for innovative strategies in the prevention and treatment of cardiovascular complications, especially in the context of T2DM.

Primary Role of the Kidney in Pathogenesis of Hypertension

Previous transplantation studies and the concept of 'nephron underdosing' support the idea that the kidney plays a crucial role in the development of essential hypertension. This suggests that there are genetic factors in the kidney that can either elevate or decrease blood pressure. The kidney normally maintains arterial pressure within a narrow range by employing the mechanism of pressure-natriuresis. Hypertension is induced when the pressure-natriuresis mechanism fails due to both subtle and overt kidney abnormalities. The inheritance of hypertension is believed to be polygenic, and essential hypertension may result from a combination of genetic variants that code for renal tubular sodium transporters or proteins involved in regulatory pathways. The renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS) are the major regulators of renal sodium reabsorption. Hyperactivity of either the RAAS or SNS leads to a rightward shift in the pressure-natriuresis curve. In other words, hypertension is induced when the activity of RAAS and SNS is not suppressed despite increased salt intake. Sodium overload, caused by increased intake and/or reduced renal excretion, not only leads to an expansion of plasma volume but also to an increase in systemic vascular resistance. Endothelial dysfunction is caused by an increased intracellular Na+ concentration, which inhibits endothelial nitric oxide (NO) synthase and reduces NO production. The stiffness of vascular smooth muscle cells is increased by the accumulation of intracellular Na+ and subsequent elevation of cytoplasmic Ca++ concentration. In contrast to the hemodynamic effects of osmotically active Na+, osmotically inactive Na+ stimulates immune cells and produces proinflammatory cytokines, which contribute to hypertension. When this occurs in the gut, the microbiota may become imbalanced, leading to intestinal inflammation and systemic hypertension. In conclusion, the primary cause of hypertension is sodium overload resulting from kidney dysregulation.

A narrative review of the mechanisms and consequences of intermittent hypoxia and the role of advanced analytic techniques in pediatric autonomic disorders

Disorders of autonomic functions are typically characterized by disturbances in multiple organ systems. These disturbances are often comorbidities of common and rare diseases, such as epilepsy, sleep apnea, Rett syndrome, congenital heart disease or mitochondrial diseases. Characteristic of many autonomic disorders is the association with intermittent hypoxia and oxidative stress, which can cause or exaggerate a variety of other autonomic dysfunctions, making the treatment and management of these syndromes very complex. In this review we discuss the cellular mechanisms by which intermittent hypoxia can trigger a cascade of molecular, cellular and network events that result in the dysregulation of multiple organ systems. We also describe the importance of computational approaches, artificial intelligence and the analysis of big data to better characterize and recognize the interconnectedness of the various autonomic and non-autonomic symptoms. These techniques can lead to a better understanding of the progression of autonomic disorders, ultimately resulting in better care and management.