Regulation Of Arterial Blood Pressure Research Articles

Regulation of Na+ excretion and arterial blood pressure by purinergic signalling intrinsic to the distal nephron: consequences and mechanisms.

Discretionary control of Na(+) excretion is a key component of the regulation of arterial blood pressure in mammals. Sodium excretion is fine-tuned in the aldosterone-sensitive distal nephron by the activity of the epithelial Na(+) channel (ENaC). Here, ENaC functions as a final effector of the renin-angiotensin-aldosterone system (RAAS) during negative feedback control of blood pressure. Mutations affecting ENaC activity and abnormal regulation of this channel affect blood pressure through pathological changes to Na(+) excretion. Recent evidence demonstrates that powerful signalling pathways function in parallel with the RAAS to modulate ENaC activity and blood pressure. An inclusive paradigm is emerging with respect to regulation of blood pressure where ENaC serves as a critical point of convergence for several important signalling systems that affect renal Na(+) excretion. A robust inhibitory purinergic signalling system intrinsic to the distal nephron dynamically regulates ENaC through paracrine ATP signalling via the metabotropic P2Y2 purinergic receptor to properly match urinary Na(+) excretion to dietary Na(+) intake. This enables blood pressure to be maintained within a normal range despite broad changes in dietary Na(+) consumption. Loss of purinergic inhibition of ENaC increases blood pressure by causing inappropriate Na(+) excretion. In contrast, stimulation of the P2Y2 receptor promotes natriuresis and a decrease in blood pressure. Such observations identify purinergic signalling in the distal nephron as possibly causative, when dysfunctional, for certain forms of elevated blood pressure, and as a possible therapeutic target for the treatment of elevated blood pressure particularly that associated with salt sensitivity.

Abstract 335: Prostaglandin I 2 Receptor Blockade Contracts Rat Renal Arteries and Facilitates Endothelium-Dependent Contractions.

Endothelium-dependent contractions are augmented in human hypertension and in isolated preparations, including renal arteries, from hypertensive animals. Renal vasomotor tone is essential in the regulation of arterial blood pressure and renal arteries are highly sensitive to vasoconstrictor prostanoids including prostacyclin, identified as endothelium-derived contracting factor (EDCF) activating thromboxane prostanoid (TP) receptors. However, the mechanisms underlying increased EDCF responses in hypertension are not completely resolved. Isometric tension was measured, in wire myographs, in renal arterial rings from spontaneously hypertensive (SHR) and age (38-52 weeks)-matched Wistar Kyoto (WKY) rats. Responses were compared under control conditions and after incubation with indomethacin (10 -5 mol/L, cyclooxygenase inhibitor), ketanserin (10 -6 mol/L, 5-HT 2 receptor antagonist), CAY10441 (10 -6 mol/L, prostaglandin I 2 [IP] receptor antagonist), and S18886 (10 -7 mol/L, TP receptor antagonist). All experiments were performed in the presence of L-NAME (3 x 10 -4 mol/L) to exclude effects of endothelium-derived NO. Surprisingly, CAY10441 (10 -10 to 10 -6 mol/L) contracted renal arterial rings from both strains; the contraction at the highest concentration was significantly larger in SHR (15±0.7 mN) than in WKY (10±1.5 mN) preparations ( n =10, P <0.05). This phenomenon was blunted by indomethacin, ketanserin, but not S18886. After washout and re-incubation, EDCF responses to acetylcholine (10 -8 to 10 -4 mol/L) were similar between SHR and WKY preparations in the presence of CAY10441 ( E max 72.6±5.3% and 67.4±3.8% KCl, n =8), but significantly larger than under control conditions ( n =4-8, P <0.05). S18886 prevented EDCF responses in the absence but not in the presence of CAY10441. Contractions to prostacyclin [in the presence of indomethacin] were facilitated by CAY10441 in rings from both strains and no longer prevented by S18886, although the TP receptor antagonist abolished contractions to U46619 (10 -11 to 3 x 10 -6 mol/L). These data suggest that: a) inhibitory IP receptors reduce renal vasomotor tone; b) IP and TP receptors form heterodimers; and c) endogenous serotonin contributes to the action of prostacyclin in rat renal arteries.

Vascular endothelial function and blood pressure regulation in afferent autonomic failure.

Familial dysautonomia (FD) is a rare hereditary disease characterized by loss of afferent autonomic neural fiber signaling and consequent profound impairment of arterial baroreflex function and blood pressure regulation. Whether vascular endothelial dysfunction contributes to defective vasomotor control in this form of afferent autonomic failure is not known. We assessed blood pressure response to orthostatic stress and vascular endothelial function with brachial artery reactivity testing in 34 FD subjects with afferent autonomic failure and 34 healthy control subjects. Forty-four percent of the afferent autonomic failure subjects had uncontrolled hypertension at supine rest (median systolic blood pressure = 148mm Hg, interquartile range (IQR) = 144-155mm Hg; median diastolic blood pressure = 83mm Hg, IQR = 78-105mm Hg), and 88% had abnormal response to orthostatic stress (median decrease in systolic blood pressure after upright tilt = 48mm Hg, IQR = 29-61mm Hg). Flow-mediated brachial artery reactivity did not differ in subjects with afferent autonomic failure vs. healthy control subjects (median = 6.00%, IQR = 1.86-11.77%; vs. median = 6.27%, IQR = 4.65-9.34%; P = 0.75). In afferent autonomic failure subjects, brachial artery reactivity was not associated with resting blood pressure or the magnitude of orthostatic hypotension but was decreased in association with reduced glomerular filtration rate (r = 0.62; P < 0.001). Brachial artery reactivity was preserved in subjects with afferent autonomic failure despite the presence of marked blood pressure dysregulation. Comorbid renal dysfunction was associated with reduced brachial artery reactivity.

Systemic and renal oxidative stress in the pathogenesis of hypertension: modulation of long-term control of arterial blood pressure by resveratrol.

Hypertension affects over 25% of the global population and is associated with grave and often fatal complications that affect many organ systems. Although great advancements have been made in the clinical assessment and treatment of hypertension, the cause of hypertension in over 90% of these patients is unknown, which hampers the development of targeted and more effective treatment. The etiology of hypertension involves multiple pathological processes and organ systems, however one unifying feature of all of these contributing factors is oxidative stress. Once the body's natural anti-oxidant defense mechanisms are overwhelmed, reactive oxygen species (ROS) begin to accumulate in the tissues. ROS play important roles in normal regulation of many physiological processes, however in excess they are detrimental and cause widespread cell and tissue damage as well as derangements in many physiological processes. Thus, control of oxidative stress has become an attractive target for pharmacotherapy to prevent and manage hypertension. Resveratrol (trans-3,5,4′-Trihydroxystilbene) is a naturally occurring polyphenol which has anti-oxidant effects in vivo. Many studies have shown anti-hypertensive effects of resveratrol in different pre-clinical models of hypertension, via a multitude of mechanisms that include its function as an anti-oxidant. However, results have been mixed and in some cases resveratrol has no effect on blood pressure. This may be due to the heavy emphasis on peripheral vasodilator effects of resveratrol and virtually no investigation of its potential renal effects. This is particularly troubling in the arena of hypertension, where it is well known and accepted that the kidney plays an essential role in the long term regulation of arterial pressure and a vital role in the initiation, development and maintenance of chronic hypertension. It is thus the focus of this review to discuss the potential of resveratrol as an anti-hypertensive treatment via amelioration of oxidative stress within the framework of the fundamental physiological principles of long term regulation of arterial blood pressure.

Estrogen status and the renin angiotensin aldosterone system.

The renin-angiotensin-aldosterone system (RAAS) is integrally involved in multiple cardiovascular physiological processes including arterial blood pressure (BP) regulation. Over activity of the RAAS has been implicated in the pathogenesis of a number of cardiovascular disease entities, including hypertension. Several lines of evidence suggest estrogen favorably modulates the RAAS. Conversely, estrogen deficiency due to menopause may contribute to over activity of the RAAS. Of importance, estrogen deficiency in women is not exclusive to the postmenopausal period. Functional hypothalamic amenorrhea is a reversible cause of premenopausal hypoestrogenemia. In contrast to postmenopausal women (PMW), premenopausal women with exercise-associated functional hypothalamic amenorrhea demonstrate decreased, not increased, resting BP compared with their estrogen-replete eumenorrheic counterpart. In this review we briefly examine the effects of estrogen status on the RAAS and present the hypothesis that the RAAS is altered in physically active women with functional hypothalamic amenorrhea.

Pulmonary Hypertension in Wild Type Mice and Animals with Genetic Deficit in KCa2.3 and KCa3.1 Channels

ObjectiveIn vascular biology, endothelial KCa2.3 and KCa3.1 channels contribute to arterial blood pressure regulation by producing membrane hyperpolarization and smooth muscle relaxation. The role of KCa2.3 and KCa3.1 channels in the pulmonary circulation is not fully established. Using mice with genetically encoded deficit of KCa2.3 and KCa3.1 channels, this study investigated the effect of loss of the channels in hypoxia-induced pulmonary hypertension.Approach and ResultMale wild type and KCa3.1−/−/KCa2.3T/T(+DOX) mice were exposed to chronic hypoxia for four weeks to induce pulmonary hypertension. The degree of pulmonary hypertension was evaluated by right ventricular pressure and assessment of right ventricular hypertrophy. Segments of pulmonary arteries were mounted in a wire myograph for functional studies and morphometric studies were performed on lung sections. Chronic hypoxia induced pulmonary hypertension, right ventricular hypertrophy, increased lung weight, and increased hematocrit levels in either genotype. The KCa3.1−/−/KCa2.3T/T(+DOX) mice developed structural alterations in the heart with increased right ventricular wall thickness as well as in pulmonary vessels with increased lumen size in partially- and fully-muscularized vessels and decreased wall area, not seen in wild type mice. Exposure to chronic hypoxia up-regulated the gene expression of the KCa2.3 channel by twofold in wild type mice and increased by 2.5-fold the relaxation evoked by the KCa2.3 and KCa3.1 channel activator NS309, whereas the acetylcholine-induced relaxation - sensitive to the combination of KCa2.3 and KCa3.1 channel blockers, apamin and charybdotoxin - was reduced by 2.5-fold in chronic hypoxic mice of either genotype.ConclusionDespite the deficits of the KCa2.3 and KCa3.1 channels failed to change hypoxia-induced pulmonary hypertension, the up-regulation of KCa2.3-gene expression and increased NS309-induced relaxation in wild-type mice point to a novel mechanism to counteract pulmonary hypertension and to a potential therapeutic utility of KCa2.3/KCa3.1 activators for the treatment of pulmonary hypertension.

Smooth muscle specific Rac1 deficiency induces hypertension by preventing p116RIP3-dependent RhoA inhibition.

BackgroundIncreasing evidence implicates overactivation of RhoA as a critical component of the pathogenesis of hypertension. Although a substantial body of work has established that Rac1 functions antagonize RhoA in a broad range of physiological processes, the role of Rac1 in the regulation of vascular tone and blood pressure is not fully elucidated.Methods and ResultsTo define the role of Rac1 in vivo in vascular smooth muscle cells (vSMC), we generated smooth muscle (SM)‐specific Rac1 knockout mice (SM‐Rac1‐KO) and performed radiotelemetric blood pressure recordings, contraction measurements in arterial rings, vSMC cultures and biochemical analyses. SM‐Rac1‐KO mice develop high systolic blood pressure sensitive to Rho kinase inhibition by fasudil. Arteries from SM‐Rac1‐KO mice are characterized by a defective NO‐dependent vasodilation and an overactivation of RhoA/Rho kinase signaling. We provide evidence that Rac1 deletion‐induced hypertension is due to an alteration of cGMP signaling resulting from the loss of Rac1‐mediated control of type 5 PDE activity. Consequently, cGMP‐dependent phosphorylation and binding of RhoA with its inhibitory partner, the phosphatase‐RhoA interacting protein (p116RIP3), are decreased.ConclusionsOur data reveal that the depletion of Rac1 in SMC decreases cGMP‐dependent p116RIP3/RhoA interaction and the subsequent inhibition of RhoA signaling. Thus, we unveil an in vivo role of Rac1 in arterial blood pressure regulation and a new pathway involving p116RIP3 that contributes to the antagonistic relationship between Rac1 and RhoA in vascular smooth muscle cells and their opposite roles in arterial tone and blood pressure.

Vascular relaxation induced by C-type natriuretic peptide involves the ca2+/NO-synthase/NO pathway.

AimsC-type natriuretic peptide (CNP) and nitric oxide (NO) are endothelium-derived factors that play important roles in the regulation of vascular tone and arterial blood pressure. We hypothesized that NO produced by the endothelial NO-synthase (NOS-3) contributes to the relaxation induced by CNP in isolated rat aorta via activation of endothelial NPR-C receptor. Therefore, the aim of this study was to investigate the putative contribution of NO through NPR-C activation in the CNP induced relaxation in isolated conductance artery.Main MethodsConcentration-effect curves for CNP were constructed in aortic rings isolated from rats. Confocal microscopy was used to analyze the cytosolic calcium mobilization induced by CNP. The phosphorylation of the residue Ser1177 of NOS was analyzed by Western blot and the expression and localization of NPR-C receptors was analyzed by immunohistochemistry.Key FindingsCNP was less potent in inducing relaxation in denuded endothelium aortic rings than in intact ones. L-NAME attenuated the potency of CNP and similar results were obtained in the presence of hydroxocobalamin, an intracellular NO0 scavenger. CNP did not change the phosphorylation of Ser1177, the activation site of NOS-3, when compared with control. The addition of CNP produced an increase in [Ca2+]c in endothelial cells and a decrease in [Ca2+]c in vascular smooth muscle cells. The NPR-C-receptors are expressed in endothelial and adventitial rat aortas.SignificanceThese results suggest that CNP-induced relaxation in intact aorta isolated from rats involves NO production due to [Ca2+]c increase in endothelial cells possibly through NPR-C activation expressed in these cells. The present study provides a breakthrough in the understanding of the close relationship between the vascular actions of nitric oxide and CNP.

Pharmacologic Role of Vitamin D Natural Products

Vitamin D is essential for maintaining a healthy mineral and bone metabolism. It stimulates calcium and phosphate absorption by the intestine, regulates bone metabolism, and negatively controls PTH secretion through the endocrine action of its active metabolite calcitriol. Vitamin D also possesses a variety of effects unrelated with mineral and bone metabolism, including the regulation of arterial blood pressure and the prevention of cardiovascular complications, modulation of immunological responses, regulation of insulin production and prevention against diabetes, protection against certain cancers, renoprotection, and other beneficial actions. This article provides an update review of the sources and pharmacological characteristics of natural vitamin D compounds, their most clinical uses, and their most important clinical results.

Influence of the baroreflex on the evolution of ventriculo arterial coupling (681.3)

The Baroreflex is a negative feedback mechanism that controls arterial blood pressure, as sensed by the baroreceptors, increasing or decreasing sympathetic and parasympathetic activity to restore arterial blood pressure. It is an important component of arterial blood pressure and circulatory regulation and therefore a fundamental mechanism in the pathogenesis of Hypertension and Congestive Heart Failure, that is further stressed by the multiple therapeutic approaches designed to influence it. As the Baroreflex influences the heart rate, cardiac contractility and vascular resistance, we hypothesised that it must influence the mechanical interaction between the left ventricle and the arterial tree as well as cardiac energy consumption and efficiency.The ventriculoarterial coupling was evaluated on a beat‐per‐beat basis, upon the application of a left‐carotid sinus baroreflex stimulus in rabbits. The left ventricle end‐systolic elastance and arterial elastance were calculated and the coupling ratio was then related to the indexes of cardiac energetics. Upon the application of the baroreflex, the coupling ratio showed an approximately linear increase, attributed to the rise in ventricular elastance. Stroke work and cardiac efficiency both increased, indicating that not only was the stroke work greater, but it was obtained at a lower oxygen cost. The coupling ratio increased indicating that it was moving towards an optimal stroke work.In conclusion the baroreflex is a control mechanism of the cardiovascular system that exerts a feedback modulation on the arterial pressure through a balanced increase in cardiac contractility and arterial input impedance which results in an improvement in ventriculo arterial coupling, mechanical and energetic efficiency.This approach can now be applied to test acute interventions on the circulatory system, including the short term reflexes as mechano reflexes and chemoreflexes, diseases such as myocardial infarction, drug and device therapy.Grant Funding Source: Fundaçao Ciencia e Tecnologia

Increased carotid‐cardiac response latency during whole‐body heat stress does not impair arterial blood pressure regulation (852.7)

Reduced orthostatic tolerance during whole‐body heating (WBH) is well‐documented. However, the impact of WBH on dynamic blood pressure regulation [e.g., carotid baroreflex (CBR) function] is not completely understood. Increased latency of carotid‐cardiac responses (i.e., time‐to‐peak of the heart rate responses) during WBH has been reported. However, the consequence of increased carotid‐cardiac latency on arterial blood pressure regulation has not been studied. We tested the hypothesis that changes in carotid‐cardiac latency during WBH would not impair arterial blood pressure regulation. Ten subjects underwent multiple 5‐sec trials of neck pressure (NP: +45 Torr, simulated hypotension) and neck suction (NS: ‐80 Torr, simulated hypertension) at rest during normothermia and passive WBH conditions (tube‐lined perfusion suit, ∆ core temp ~1 °C). CBR latency was determined by summing the r‐r intervals from the onset of the respective stimuli to the initial r wave of the cardiac cycle associated with the peak heart rate responses. Carotid‐cardiac latency to NP was increased during WBH (4.1±0.4) compared to normothermia (2.8±0.5sec, P&lt;0.05). Carotid‐cardiac latency to NS was not different between thermal conditions (P=0.40). To determine if the greater latency in response to NP impaired CBR control of blood pressure, the mean arterial pressure (MAP) at the time of the peak HR response during normothermia was compared to the MAP that occurred at the same time‐point of the WBH trials. As hypothesized, the MAP accompanying the peak HR response during normothermia (5.6±4.4) was not different than the increase in blood pressure at the same time‐point during WBH (4.0±3.6mm Hg, P=0.25). Despite the increased carotid‐cardiac latency during WBH in response to simulated hypotension, CBR control of blood pressure was not negatively influenced. It does not appear that changes in carotid‐cardiac responsiveness are responsible for the reduced orthostatic tolerance during whole‐body heat stress.

T-type Ca2+ channels facilitate NO-formation, vasodilatation and NO-mediated modulation of blood pressure

Voltage-gated calcium channels are involved in the vascular excitation-contraction mechanism and regulation of arterial blood pressure. It was hypothesized that T-type channels promote formation of nitric oxide from the endothelium. The present experiments determine the involvement of T-type channels in depolarization-dependent dilatation of mesenteric arteries and blood pressure regulation in Cav3.1 knock-out mice. Nitric oxide-dependent vasodilatation following depolarization-mediated vasoconstriction was reduced significantly in mesenteric arteries from Cav3.1(-/-) compared to wild type mice. Four days of systemic infusion of a nitric oxide (NO)-synthase-inhibitor to conscious wild type elicited a significant increase in mean arterial blood pressure that was absent in Cav3.1(-/-) mice. Immunoprecipitation and immunofluorescence labeling showed co-localization of Cav3.1 and endothelial nitric oxide synthase (eNOS) in arteries from wild type mice. Nitric oxide release measured as DAF fluorescence and cGMP levels were significantly lower in depolarized Cav3.1(-/-) compared to wild type arteries. In summary, the absence of T-type Cav3.1 channels attenuates NO-dependent dilatation in mesenteric arteries in vitro, as well as the hypertension after L-NAME infusion in vivo. Furthermore, Cav3.1 channels cluster with eNOS and promote formation of nitric oxide by the endothelium. The present findings suggest that this mechanism is important for the systemic impact of NO on peripheral resistance.

Leptin in Association With Common Variants of MC3R Mediates Hypertension

Recent research illustrates the role of central melanocortin signaling and leptin in the regulation of arterial blood pressure in animal models. Unraveling the genetic basis of interactions between melanocortin and leptin in humans will provide new insight into the regulation of arterial pressure. Our study population consisted of 332 Kuwaiti natives. Polymorphisms from exons of leptin, MC3R, and MC4R genes were identified by Sanger sequencing. MC3R expression and leptin levels were determined. Linear regression models, adjusted for age, gender, antihypertensive medication, and body mass index, were used to perform statistical association tests. We observed a significant association between the MC3R missense variant (rs3827103 [Val81 Ile]) and systolic blood pressure (SBP; P = 0.01, β = 4.9). The N-terminus variant (rs3746619 [Thr6→Lys]) is in linkage disequilibrium (r2 = 0.65) with the rs3827103 variant. The AA haplotype of rs3746619-rs3827103 is significantly associated with SBP (P = 0.005, β=5.03). Minor allele frequencies of these two variants in the Kuwaiti population are twice those seen in European population. In individuals who harbor these variants, we found that the plasma leptin levels were positively correlated with SBP and that the expression of MC3R was downregulated. Leptin levels correlated with obesity traits irrespective of the genotypes at the variant positions. An increase in leptin levels is known to increase sympathetic nerve activity that, in turn, increases blood pressure. Thus, it is possible that the observed MC3R variants in association with leptin levels are involved in regulation of blood pressure in humans.

Blood borne hormones in a cross-talk between peripheral and brain mechanisms regulating blood pressure, the role of circumventricular organs

Accumulating evidence suggests that blood borne hormones modulate brain mechanisms regulating blood pressure. This appears to be mediated by the circumventricular organs which are located in the walls of the brain ventricular system and lack the blood–brain barrier. Recent evidence shows that neurons of the circumventricular organs express receptors for the majority of cardiovascular hormones. Intracerebroventricular infusions of hormones and their antagonists is one approach to evaluate the influence of blood borne hormones on the neural mechanisms regulating arterial blood pressure. Interestingly, there is no clear correlation between peripheral and central effects of cardiovascular hormones. For example, angiotensin II increases blood pressure acting peripherally and centrally, whereas peripherally acting pressor catecholamines decrease blood pressure when infused intracerebroventricularly. The physiological role of such dual hemodynamic responses has not yet been clarified.In the paper we review studies on hemodynamic effects of catecholamines, neuropeptide Y, angiotensin II, aldosterone, natriuretic peptides, endothelins, histamine and bradykinin in the context of their role in a cross-talk between peripheral and brain mechanisms involved in the regulation of arterial blood pressure.

Renalase mRNA levels in the brain, heart, and kidneys of spontaneously hypertensive rats with moderate and high hypertension

BackgroundRenalase is a recently discovered secretory protein involved in regulation of arterial blood pressure in humans and animals. Results of animal experiments from independent laboratories indicate that administration of human recombinant renalase decreases blood pressure and some genetically predisposed hypertensive rats have lowered renalase levels.Material/MethodsThe levels of renalase mRNA expression in brain hemispheres, heart, and kidneys of spontaneously hypertensive rats (SHR) with moderate (140–180 mm Hg) or high (>180 mm Hg) hypertension and of control Wistar-Kyoto (WKY) rats were analyzed using real-time PCR.ResultsSpontaneously hypertensive rats with high hypertension (>180 mm Hg) had a lower renalase mRNA level in brain hemispheres, and higher heart and kidney renalase mRNA levels compared with control WKY rats. In SHR with a moderate increase in arterial blood pressure (140–180 mm Hg), the tissue renalase mRNA changed in the same direction but did not reach the level of statistical significance as compared with control rats.ConclusionsThe results indicate that the development of hypertension in SHR is accompanied by altered expression of the renalase gene in the examined organs as compared with control WKY rats. The brain and peripheral tissues renalase mRNA levels demonstrate opposite trends, which are obviously crucial for impaired regulation of blood pressure in SHR.

Dual actions of ANP on endothelial permeability

Atrial natriuretic peptide (ANP), via its cGMP-forming guanylyl cyclase-A (GC-A) receptor, is critically involved in the regulation of arterial blood pressure and intravascular volume. To elucidate the role of the endothelial effects of ANP, we generated mice with conditional, endothelium (EC)-restricted ablation of the GC-A gene. Our observations in these and control mice demonstrated that ANP, via GC-A, mildly stimulates systemic transendothelial albumin transport in the microvasculature of skeletal muscle and skin. These and other studies indicate that concerted renal diuretic/natriuretic and mild endothelial hyperpermeability actions of ANP are essential to adjust intravascular fluid volume. However, this notion apparently contradicts published in vitro and in vivo studies showing that ANP can strenghen the pulmonary barrier under inflammatory conditions, suggesting that the hormone either acts differently on pulmonary vs systemic endothelium, or it exerts opposite effects on quiescent endothelia (enhanced permeability) and an inflammation-activated endothelium (barrier stabilization). Endothelial hyperpermeability is characteristic of many systemic diseases, such as allergic responses, edema, and sepsis. In particular, histamine markedly and acutely enhances endothelial permeability. Activation of endothelial Gq-coupled H1 receptors activates phospholipase C and elevates intracellular [Ca2+], ultimately leading to actin-myosin contraction and paracellular leakiness. Here we combined studies in microvascular endothelial cells and intravital microscopy of vascular permeability in the m. cremaster microcirculation to study whether ANP counteracts not only pulmonary but also systemic inflammation, i.e. histamine-induced hyperpermeability. Our observations reveal that transient receptor potential canonical (TRPC) 6 channels mediate the inflammatory effects of histamine. Most importantly, they characterize a regulatory pathway by which histamine-induced activation of TRPC6 channels and subsequent calcium-dependent acute endothelial hyperpermeability are prevented by ANP/GC-A-induced, cGMP-dependent protein kinase I (cGKI) - mediated inhibitory phosphorylation of these channels.

Aldosterone-dependenttrans-activation and epigenetic derepression of ENaC: where is the balance?

the critical role of the kidney collecting duct and the epithelial Na+ channel (ENaC) in the regulation of arterial blood pressure has been recognized for many years (5). However, the factors that alter renal function and the pathways involved remain to be determined. The mineralocorticoid hormone aldosterone increases tubular sodium absorption in large part by increasing α-ENaC transcription. The pioneering demonstration of epigenetic regulation of ENaC was published by the Kone's laboratory several years ago, when it was reported that a complex containing the histone H3K79 methyltransferase disruptor of telomeric silencing-1 (Dot1) associates with and represses the α-ENaC promoter and that aldosterone and serum- and glucocorticoid-induced kinase-1 (Sgk1) act to disrupt this complex and its inhibitory effects (8, 9). Following studies indicated that either Af9 (in humans, encoded by MLLT3) or Sirt1 (encoded by SIRT1) directly binds to +78/+92 of α-ENaC and recruits Dot1a to repress basal and aldosterone-sensitive α-ENaC transcription (7, 10). Despite this epigenetic repression, basal α-ENaC transcription is still evident and physiologically necessary, indicating basal operation of positive regulators. In an issue of the American Journal of Physiology-Renal Physiology, Kone and associates (6) provide evidence that begins to clarify this gap in knowledge and show that Sp1 is one of such positive regulators. Sp1, a promoter-specific factor required for transcription of the SV40 early and late promoters, was the first cloned mammalian transcription factor (2). Sp1 clearly has functional importance, since gene disruption in mice is lethal (3). Sp1, a candidate transcription factor, chosen based on sequence analysis of the α-ENaC promoter, binds to the α-ENaC promoter at a single, specific transcription factor binding site (a cis-element at +222/+229). Thus, Sp1 represents the first described constitutive driver of α-ENaC transcription, which also contributes to maximal aldosterone trans-activation of α-ENaC. Importantly, presented data complement the previous observations of this group. Additional experiments were done to study the role of Sp1 into the context of Dot1a-mediated repression of transcription or aldosterone-mediated induction of α-ENaC transcription. The authors reported that Sp1 acts independently from and overcomes the Dot1a-Af9 repressor complex (Fig. 1). Thus, the model and studies reflect the balance of genetic and epigenetic factors: Sp1 acting on the promoter DNA being the former, and Dot1 acting on histones being the latter. Surprisingly, the authors did not try to place in the global picture regulation of the transcription of ENaC genes by Af17, which competes with Af9 for binding to Dot1a to upregulate transcription of α-ENaC (4) and regulate ENaC-mediated sodium reabsorption and blood pressure (1). Fig. 1. Simplified model for the aldosterone-sensitive regulation of α-epithelial Na+ channel (ENaC) expression. Af9 directly binds +78/+92 of the α-ENaC promoter and recruits Dot1a to this position to basally repress α-ENaC transcription. ... This manuscript presents direct evidence of regulation of α-ENaC by Sp1 and highlights the need for further investigation of mechanisms that initiate or repress transcription of genes encoding ENaC subunits. A few questions are raised from the current study. First, this study is focused on Sp1, but it cannot exclude the possibility that other related factors also interact with the GAGGGCGT boxes of the α-ENaC promoter. Sp1 is part of a large family of proteins, including other Sp factors and the extensive set of Kruppel-like factors. Some of these factors are expressed and functionally important in the cardiorenal system. These factors might have a greater influence than Sp1, either as coactivators, or dominant-negative competitors with Sp1, like Af17, which competes with AF9 for binding to Dot1a (4). Similarly, it is not clear whether Sp1 plays a unique role in regulation of maximal aldosterone-dependent trans-activation of α-ENaC and how other factors like SGK1 modulate this regulation. Furthermore, current studies are performed in cultured mouse inner medullary collecting duct 3 cells in vitro. It would be nice if these findings will be further confirmed in vivo, similar to a recent study where the mice with connecting tubule/cortical collecting duct-specific inactivation of Dot1a revealed greater α-ENaC mRNA levels compared with control (10). Moreover, the functional correlation would improve the physiological significance of these molecular studies. Additional experiments are required to determine whether the Sp1 is functionally important in regulating ENaC or not by overexpressing or knocking down Sp1 and measuring a channel's activity. In conclusion, this study by Yu et al. (6) implicates a key role for the transcription factor Sp1 in regulation of ENaC. The authors propose a mechanism whereby endogenous Sp1 factor is functionally involved in conferring constitutive expression and aldosterone regulation of α-ENaC gene. Sp1 has the potential to be a critical point for understanding the physiological control of ENaC gene expression in the kidney. Importantly, this study is one of the first steps in understanding of genetic and epigenetic regulation of ENaC and emphasizes the need for further investigation of this important area of research.

Hypothalamic mTORC1 Signaling Controls Sympathetic Nerve Activity and Arterial Pressure and Mediates Leptin Effects

The fundamental importance of the hypothalamus in the regulation of autonomic and cardiovascular functions is well established. However, the molecular processes involved are not well understood. Here, we show that the mammalian (or mechanistic) target of rapamycin (mTOR) signaling in the hypothalamus is tied to the activity of the sympathetic nervous system and to cardiovascular function. Modulation of mTOR complex 1 (mTORC1) signaling caused dramatic changes in sympathetic traffic, blood flow, and arterial pressure. Our data also demonstrate the importance of hypothalamic mTORC1 signaling in transducing the sympathetic and cardiovascular actions of leptin. Moreover, we show that the PI3K pathway links the leptin receptor to mTORC1 signaling and that changes in its activity impact sympathetic traffic and arterial pressure. These findings establish mTORC1 activity in the hypothalamus as a key determinant of sympathetic and cardiovascular regulation and suggest that dysregulated hypothalamic mTORC1 activity may influence the development of cardiovascular diseases.

Intracellular angiotensin II increases the total potassium current and the resting potential of arterial myocytes from vascular resistance vessels of the rat. Physiological and pathological implications

The influence of intracellular and extracellular administration of angiotensin II (Ang II; 10−9 M) on total potassium current of arterial myocytes isolated from mesenteric arteries of Sprague Dawley rats was investigated. Measurements of total potassium current were performed using the voltage clamp whole cell configuration while the effect of intracellular Ang II on the resting potential of arterial myocytes was measured using the current clamp configuration of pCLAMP. The results indicated that: 1) intracellular Ang II (10−9 M) increased the total potassium current by 73% ± 2.6% (n = 22; P < .05) within 5 minutes; 2) concurrently with the increment of potassium current, the resting potential was increased by 7 ± 1.5 mV (n = 23; P < .05); 3) extracellular administration of Ang II (10−9 M) reduced the total potassium current by 20% ± 1.6% (n = 21; P < .05) within 5 minutes and depolarized the smooth muscle cells by 9 ± 2.3 mV (n = 26; P < .05); 4) the effects of intracellular Ang II on potassium current and membrane potential were inhibited by dialyzing a PKA inhibitor (10-9 M) inside the cell together with Ang II (10−9 M; P > .05); 5) valsartan (10−9 M) dialyzed into the cell together with Ang II (10−9 M) abolished the effect of the peptide on potassium current and membrane potential. The presence of endogenous or internalized intracellular Ang II in vascular resistance vessels and its effect on potassium current and resting potential indicates that the peptide present inside the arterial myocytes plays an important role on the regulation of vascular tone and consequently on peripheral resistance, which is a determining factor in the regulation of arterial blood pressure.

Erratum to: Regulation of arterial blood pressure by Akt1-dependent vascular relaxation

In Fig. 2a, reporting data from immunohistochemistry, the image of total eNOS staining in the NT condition was published incorrectly. Specifically, it was duplicated from the PDGF condition by mistake. In the corrected version of Fig. 2a, the image was replaced appropriately. The authors claim that this correction does not affect the message and conclusion of this study, and would like to apologize for this oversight.