Cellular mechanism of endothelin-1 release by angiotensin and vasopressin

Endothelial dysfunction and persistent inflammation in severe post-COVID-19 patients: implications for gas exchange

BACKGROUND

Understanding the enduring respiratory consequences of severe COVID-19 is crucial for comprehensive patient care. This study aims to evaluate the impact of post-COVID conditions on respiratory sequelae of severe acute respiratory distress syndrome (ARDS).

METHODS

We examined 88 survivors of COVID-19-associated severe ARDS six months post-intensive care unit (ICU) discharge. Assessments included clinical and functional evaluation as well as plasma biomarkers of endothelial dysfunction, inflammation, and viral response. Additionally, an in vitro model using human umbilical vein endothelial cells (HUVECs) explored the direct impact of post-COVID plasma on endothelial function.

RESULTS

Post-COVID patients with impaired gas exchange demonstrated persistent endothelial inflammation marked by elevated ICAM-1, IL-8, CCL-2, and ET-1 plasma levels. Concurrently, systemic inflammation, evidenced by NLRP3 overexpression and elevated levels of IL-6, sCD40-L, and C-reactive protein, was associated with endothelial dysfunction biomarkers and increased in post-COVID patients with impaired gas exchange. T-cell activation, reflected in CD69 expression, and persistently elevated levels of interferon-β (IFN-β) further contributed to sustained inflammation. The in vitro model confirmed that patient plasma, with altered levels of sCD40-L and IFN-β proteins, has the capacity to alter endothelial function.

CONCLUSIONS

Six months post-ICU discharge, survivors of COVID-19-associated ARDS exhibited sustained elevation in endothelial dysfunction biomarkers, correlating with the severity of impaired gas exchange. NLRP3 inflammasome activity and persistent T-cell activation indicate on going inflammation contributing to persistent endothelial dysfunction, potentially intensified by sustained viral immune response.

Mechanism of protective actions of sparsentan in the kidney: lessons from studies in models of chronic kidney disease

Simultaneous inhibition of angiotensin II AT1 and endothelin ETA receptors has emerged as a promising approach for treatment of chronic progressive kidney disease. This therapeutic approach has been advanced by the introduction of sparsentan, the first dual AT1 and ETA receptor antagonist. Sparsentan is a single molecule with high affinity for both receptors. It is US Food and Drug Administration approved for immunoglobulin A nephropathy (IgAN) and is currently being developed as a treatment for rare kidney diseases, such as focal segmental glomerulosclerosis. Clinical studies have demonstrated the efficacy and safety of sparsentan in these conditions. In parallel with clinical development, studies have been conducted to elucidate the mechanisms of action of sparsentan and its position in the context of published evidence characterizing the nephroprotective effects of dual ETA and AT1 receptor inhibition. This review summarizes this evidence, documenting beneficial anti-inflammatory, antifibrotic, and hemodynamic actions of sparsentan in the kidney and protective actions in glomerular endothelial cells, mesangial cells, the tubulointerstitium, and podocytes, thus providing the rationale for the use of sparsentan as therapy for focal segmental glomerulosclerosis and IgAN and suggesting potential benefits in other renal diseases, such as Alport syndrome.

An endothelial regulatory module links blood pressure regulation with elite athletic performance

The control of transcription is crucial for homeostasis in mammals. A previous selective sweep analysis of horse racing performance revealed a 19.6 kb candidate regulatory region 50 kb downstream of the Endothelin3 (EDN3) gene. Here, the region was narrowed to a 5.5 kb span of 14 SNVs, with elite and sub-elite haplotypes analyzed for association to racing performance, blood pressure and plasma levels of EDN3 in Coldblooded trotters and Standardbreds. Comparative analysis of human HiCap data identified the span as an enhancer cluster active in endothelial cells, interacting with genes relevant to blood pressure regulation. Coldblooded trotters with the sub-elite haplotype had significantly higher blood pressure compared to horses with the elite performing haplotype during exercise. Alleles within the elite haplotype were part of the standing variation in pre-domestication horses, and have risen in frequency during the era of breed development and selection. These results advance our understanding of the molecular genetics of athletic performance and vascular traits in both horses and humans.

Angiotensin II Directly Increases Endothelial Calcium and Nitric Oxide in Kidney and Brain Microvessels In Vivo With Reduced Efficacy in Hypertension

BACKGROUND

The vasoconstrictor effects of angiotensin II via type 1 angiotensin II receptors in vascular smooth muscle cells are well established, but the direct effects of angiotensin II on vascular endothelial cells (VECs) in vivo and the mechanisms how VECs may mitigate angiotensin II-mediated vasoconstriction are not fully understood. The present study aimed to explore the molecular mechanisms and pathophysiological relevance of the direct actions of angiotensin II on VECs in kidney and brain microvessels in vivo.

METHODS AND RESULTS

Changes in VEC intracellular calcium ([Ca2+]i) and nitric oxide (NO) production were visualized by intravital multiphoton microscopy of cadherin 5-Salsa6f mice or the endothelial uptake of NO-sensitive dye 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, respectively. Kidney fibrosis by unilateral ureteral obstruction and Ready-to-use adeno-associated virus expressing Mouse Renin 1 gene (Ren1-AAV) hypertension were used as disease models. Acute systemic angiotensin II injections triggered >4-fold increases in VEC [Ca2+]i in brain and kidney resistance arterioles and capillaries that were blocked by pretreatment with the type 1 angiotensin II receptor inhibitor losartan, but not by the type 2 angiotensin II receptor inhibitor PD123319. VEC responded to acute angiotensin II by increased NO production as indicated by >1.5-fold increase in 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate fluorescence intensity. In mice with kidney fibrosis or hypertension, the angiotensin II-induced VEC [Ca2+]i and NO responses were significantly reduced, which was associated with more robust vasoconstrictions, VEC shedding, and microthrombi formation.

CONCLUSIONS

The present study directly visualized angiotensin II-induced increases in VEC [Ca2+]i and NO production that serve to counterbalance agonist-induced vasoconstriction and maintain residual organ blood flow. These direct and endothelium-specific angiotensin II effects were blunted in disease conditions and linked to endothelial dysfunction and the development of vascular pathologies.

Endothelin-1 in Health and Disease

Discovered almost 40 years ago, the potent vasoconstrictor peptide endothelin-1 (ET-1) has a wide range of roles both physiologically and pathologically. In recent years, there has been a focus on the contribution of ET-1 to disease. This has led to the development of various ET receptor antagonists, some of which are approved for the treatment of pulmonary arterial hypertension, while clinical trials for other diseases have been numerous yet, for the most part, unsuccessful. However, given the vast physiological impact of ET-1, it is both surprising and disappointing that therapeutics targeting the ET-1 pathway remain limited. Strategies aimed at the pathways influencing the synthesis and release of ET-1 could provide new therapeutic avenues, yet research using cultured cells in vitro has had little follow up in intact ex vivo and in vivo preparations. This article summarises what is currently known about the synthesis, storage and release of ET-1 as well as the role of ET-1 in several diseases including cardiovascular diseases, COVID-19 and chronic pain. Unravelling the ET-1 pathway and identifying therapeutic targets has the potential to treat many diseases whether through disease prevention, slowing disease progression or reversing pathology.

Endothelin type A receptor blockade attenuates aorto-caval fistula-induced heart failure in rats with angiotensin II-dependent hypertension

OBJECTIVE

Evaluation of the effect of endothelin type A (ET A ) receptor blockade on the course of volume-overload heart failure in rats with angiotensin II-dependent hypertension.

METHODS

Ren-2 renin transgenic rats (TGR) were used as a model of hypertension. Heart failure was induced by creating an aorto-caval fistula (ACF). Selective ET A receptor blockade was achieved by atrasentan. For comparison, other rat groups received trandolapril, an angiotensin-converting enzyme inhibitor (ACEi). Animals first underwent ACF creation and 2 weeks later the treatment with atrasentan or trandolapril, alone or combined, was applied; the follow-up period was 20 weeks.

RESULTS

Eighteen days after creating ACF, untreated TGR began to die, and none was alive by day 79. Both atrasentan and trandolapril treatment improved the survival rate, ultimately to 56% (18 of 31 animals) and 69% (22 of 32 animals), respectively. Combined ACEi and ET A receptor blockade improved the final survival rate to 52% (17 of 33 animals). The effects of the three treatment regimens on the survival rate did not significantly differ. All three treatment regimens suppressed the development of cardiac hypertrophy and lung congestion, decreased left ventricle (LV) end-diastolic volume and LV end-diastolic pressure, and improved LV systolic contractility in ACF TGR as compared with their untreated counterparts.

CONCLUSION

The treatment with ET A receptor antagonist delays the onset of decompensation of volume-overload heart failure and improves the survival rate in hypertensive TGR with ACF-induced heart failure. However, the addition of ET A receptor blockade did not enhance the beneficial effects beyond those obtained with standard treatment with ACEi alone.

Peptidergic G Protein-Coupled Receptor Regulation of Adrenal Function: Bench to Bedside and Back

An altered secretion of adrenocortical and adrenomedullary hormones plays a role in the clinical syndromes of primary aldosteronism (PA), Cushing, and pheochromocytoma. Moreover, an altered production of adrenocortical hormones and/or an abnormal release of factors by the adrenal medulla are involved in several other diseases, including high blood pressure, congestive heart failure, liver cirrhosis, nephrotic syndrome, primary reninism, renovascular hypertension, Addison disease, Bartter, Gitelman, and virilization syndromes. Understanding the regulation of adrenal function and the interactions between adrenal cortex and medulla is, therefore, the prerequisite for mechanistic understanding of these disorders. Accumulating evidence indicates that the modulation of adrenal hormone biosynthesis is a process far more complex than originally thought, as it involves several factors, each cooperating with the other. Moreover, the tight vascular and neural interconnections between the adrenal cortex and medulla underlie physiologically relevant autocrine/paracrine interactions involving several peptides. Besides playing a pathophysiological role in common adrenal diseases, these complex mechanisms could intervene also in rare diseases, such as pheochromocytoma concomitant with adrenal Cushing or with PA, and PA co-occurring with Cushing, through mechanisms that remain to be fully understood at the molecular levels. Heterodimerization of G protein-coupled receptors (GPCRs) induced by peptide signaling is a further emerging new modulatory mechanism capable of finely tuning adrenal hormones synthesis and release. In this review we will examine current knowledge on the role of peptides that act via GPCRs in the regulation of adrenal hormone secretion with a particular focus on autocrine-paracrine signals.

Vasoplegic Syndrome after Cardiopulmonary Bypass in Cardiovascular Surgery: Pathophysiology and Management in Critical Care

Vasoplegic syndrome (VS) is a common complication following cardiovascular surgery with cardiopulmonary bypass (CPB), and its incidence varies from 5 to 44%. It is defined as a distributive form of shock due to a significant drop in vascular resistance after CPB. Risk factors of VS include heart failure with low ejection fraction, renal failure, pre-operative use of angiotensin-converting enzyme inhibitors, prolonged aortic cross-clamp and left ventricular assist device surgery. The pathophysiology of VS after CPB is multi-factorial. Surgical trauma, exposure to the elements of the CPB circuit and ischemia-reperfusion promote a systemic inflammatory response with the release of cytokines (IL-1β, IL-6, IL-8, and TNF-α) with vasodilating properties, both direct and indirect through the expression of inducible nitric oxide (NO) synthase. The resulting increase in NO production fosters a decrease in vascular resistance and a reduced responsiveness to vasopressor agents. Further mechanisms of vasodilation include the lowering of plasma vasopressin, the desensitization of adrenergic receptors, and the activation of ATP-dependent potassium (KATP) channels. Patients developing VS experience more complications and have increased mortality. Management includes primarily fluid resuscitation and conventional vasopressors (catecholamines and vasopressin), while alternative vasopressors (angiotensin 2, methylene blue, hydroxocobalamin) and anti-inflammatory strategies (corticosteroids) may be used as a rescue therapy in deteriorating patients, albeit with insufficient evidence to provide any strong recommendation. In this review, we present an update of the pathophysiological mechanisms of vasoplegic syndrome complicating CPB and discuss available therapeutic options.

Angiotensin peptides in the regulation of adrenal cortical function

The adrenal cortex plays a key role in the regulation of metabolism, salt and water homeostasis and sex differentiation by synthesizing glucocorticoid, mineralocorticoid and androgen hormones. Evidence exists that angiotensin II regulates adrenocortical function and it has been contended that angiotensin peptides of the non-canonical branch of the renin angiotensin system (RAS) might also modulate steroidogenesis in adrenals. Thus, the aim of this review is to examine the role of the RAS, and particularly of the angiotensin peptides and their receptors, in the regulation of adrenocortical hormones with particular focus on aldosterone production.

The growth hormone and insulin-like growth factor 1 axis in cattle during the peri-ovulatory period activates the synthesis and release of oviductal contraction related substances

Growth hormone (GH) and insulin-like growth factor 1 (IGF1) are crucial for female reproductive functions. The cyclic regulation of the local GH/IGF1 axis in the oviduct and its involvement in oviductal contraction in cattle has not been investigated. Thus, the messenger RNA (mRNA) expression for GH receptor (GHR), IGF1, IGF1 receptor (IGF1R) in the whole oviducts, as well as in cultured bovine oviductal epithelial cells (BOECs) were evaluated. The GHR, IGF1, and IGF1R mRNA expression was significantly higher during postovulatory phase. The luteinizing hormone (LH), estradiol-17β (E2), and LH + E2 treatments significantly increased GHR and IGF1 mRNA expression in cultured BOECs. Further, GH and combination of GH with LH and E2 upregulated IGF1 mRNA expression in the BOECs. Moreover, IGF1 + LH and combined IGF1 + LH + E2 treatments significantly increased prostaglandin synthesis cascade enzyme mRNA expression in the BOECs. An ex vivo microdialysis assay revealed that GH and IGF1 induced the release of oviductal contraction related prostaglandins, endothelin-1, and angiotensin II in follicular and postovulatory phases. Together, the findings strongly suggest that the presence of the active GH/IGF1 axis during the peri-ovulatory period, regulating the local system for the release of oviductal contraction related substances, which may provide the optimal oviductal environment for gametes and early embryo.

Polarized Proteins in Endothelium and Their Contribution to Function

Protein localization in endothelial cells is tightly regulated to create distinct signaling domains within their tight spatial restrictions including luminal membranes, abluminal membranes, and interendothelial junctions, as well as caveolae and calcium signaling domains. Protein localization in endothelial cells is also determined in part by the vascular bed, with differences between arteries and veins and between large and small arteries. Specific protein polarity and localization is essential for endothelial cells in responding to various extracellular stimuli. In this review, we examine protein localization in the endothelium of resistance arteries, with occasional references to other vessels for contrast, and how that polarization contributes to endothelial function and ultimately whole organism physiology. We highlight the protein localization on the luminal surface, discussing important physiological receptors and the glycocalyx. The protein polarization to the abluminal membrane is especially unique in small resistance arteries with the presence of the myoendothelial junction, a signaling microdomain that regulates vasodilation, feedback to smooth muscle cells, and ultimately total peripheral resistance. We also discuss the interendothelial junction, where tight junctions, adherens junctions, and gap junctions all convene and regulate endothelial function. Finally, we address planar cell polarity, or axial polarity, and how this is regulated by mechanosensory signals like blood flow.

Differential role of specific cardiovascular neuropeptides in pain regulation: Relevance to cardiovascular diseases

In many instances, the perception of pain is disproportionate to the strength of the algesic stimulus. Excessive or inadequate pain sensation is frequently observed in cardiovascular diseases, especially in coronary ischemia. The mechanisms responsible for individual differences in the perception of cardiovascular pain are not well recognized. Cardiovascular disorders may provoke pain in multiple ways engaging molecules released locally in the heart due to tissue ischemia, inflammation or cellular stress, and through neurogenic and endocrine mechanisms brought into action by hemodynamic disturbances. Cardiovascular neuropeptides, namely angiotensin II (Ang II), angiotensin-(1-7) [Ang-(1-7)], vasopressin, oxytocin, and orexins belong to this group. Although participation of these peptides in the regulation of circulation and pain has been firmly established, their mutual interaction in the regulation of pain in cardiovascular diseases has not been profoundly analyzed. In the present review we discuss the regulation of the release, and mechanisms of the central and systemic actions of these peptides on the cardiovascular system in the context of their central and peripheral nociceptive (Ang II) and antinociceptive [Ang-(1-7), vasopressin, oxytocin, orexins] properties. We also consider the possibility that they may play a significant role in the modulation of pain in cardiovascular diseases. The rationale for focusing attention on these very compounds was based on the following premises (1) cardiovascular disturbances influence the release of these peptides (2) they regulate vascular tone and cardiac function and can influence the intensity of ischemia - the factor initiating pain signals in the cardiovascular system, (3) they differentially modulate nociception through peripheral and central mechanisms, and their effect strongly depends on specific receptors and site of action. Accordingly, an altered release of these peptides and/or pharmacological blockade of their receptors may have a significant but different impact on individual sensation of pain and comfort of an individual patient.

Dysfunction of the endothelium and constriction of the isolated rat's middle cerebral artery in low sodium environment in the presence of vasopressin

Hyponatraemia, a water-electrolyte disorder diagnosed in patients with subarachnoid haemorrhage (SAH), increases a risk of persistent vasospasm. In majority of cases, hyponatraemia results from inappropriate secretion of vasopressin (AVP). The effect of AVP-associated hyponatraemia on cerebral vasculature is unknown. The present study aimed to elucidate the role of AVP in the response of the middle cerebral artery (MCA) of the rat to hyponatraemia. Isolated, cannulated, and pressurized rat MCAs were perfused/superfused with physiological (Na⁺  = 144 mmol/L) buffer or low-sodium (Na⁺  = 121 mmol/L) buffer containing either AVP or angiotensin II (ANG II). ANG II was used to check if the effect of low plasma sodium concentration combined with AVP on the MCA tone is unique to vasopressin. At physiological Na⁺ concentration, vasopressin (1.4 × 10^-11  mol/L) or angiotensin II (10^-9  mol/L) resulted in relaxation of the MCA. Substitution of low-sodium for the normal sodium buffer with the same concentration of AVP, resulted in the constriction of the MCA. This effect was absent after removal of the endothelium, administration of vasopressin V₁ receptor antagonist or concomitant inhibition of endothelin-1 receptors and synthesis of thromboxane A_2. In contrast, no constriction of the MCA in low-sodium buffer was observed when AVP was replaced with ANG II. Our data suggest that presence of vasopressin and low sodium ion concentration results in the change of endothelium phenotype from pro-vasodilatory to pro-vasoconstrictory. This phenomenon may be an overlooked factor contributing to vasospasm in SAH patients with hyponatraemia caused by inappropriate antidiuretic hormone secretion (SIADH).

Endothelial cell-cardiomyocyte crosstalk in heart development and disease

The crosstalk between endothelial cells and cardiomyocytes has emerged as a requisite for normal cardiac development, but also a key pathogenic player during the onset and progression of cardiac disease. Endothelial cells and cardiomyocytes are in close proximity and communicate through the secretion of paracrine signals, as well as through direct cell-to-cell contact. Here, we provide an overview of the endothelial cell-cardiomyocyte interactions controlling heart development and the main processes affecting the heart in normal and pathological conditions, including ischaemia, remodelling and metabolic dysfunction. We also discuss the possible role of these interactions in cardiac regeneration and encourage the further improvement of in vitro models able to reproduce the complex environment of the cardiac tissue, in order to better define the mechanisms by which endothelial cells and cardiomyocytes interact with a final aim of developing novel therapeutic opportunities.

Measurement of plasma endothelin-1 concentration in healthy horses and horses with cardiac disease during rest and after exercise

Cardiac biomarkers are important tools for monitoring disease progress and can monitor progression of therapy. Endothelin-1 (ET-1) has been studied for its use as a cardiac biomarker in human and small animal medicine while in horses with cardiac disease it has not been evaluated yet. The objective of the present study was to determine the concentration of plasma ET-1 in healthy horses and compare it with ET-1 concentration in horses with cardiac disease during rest and after exercise. Fifty four horses admitted to the Equine Clinic of Free University of Berlin were used in the present study, of which 15 horses were clinically healthy with no evidence of cardiac disease (Group 1), 22 horses suffered from cardiac disease with normal heart dimensions (Group 2) and 17 horses with cardiac disease and enlarged heart diameters (Group 3). Clinical examination, electrocardiography and echocardiography were performed. Endothelin-1 concentration was determined using ET-1 ELISA kit. The concentration of plasma ET-1 was significantly increased in horses with cardiac disease and normal cardiac dimensions (Group 2) and in horses with cardiac disease and enlargement of the left atrium (Group 3) compared to its concentration in clinically healthy horses (Group 1). In addition, the concentration of plasma ET-1 after exercise was significantly increased in diseased horses compared to its concentration at rest. Detection of ET-1 plasma concentration in horses at rest may be useful for detecting horses with changes in left atrial cardiac dimensions.

Endothelins and Sarafotoxins: Peptides of Similar Structure and Different Function

Endothelins are endogenous vasoactive peptides that are considered among the most potent vasoconstrictor substances known. In addition to their vascular effects, endothelins and their receptors have been shown to be present in many organs and share plenty physiological and pathophysiological functions. Sarafotoxins are natural substances from the venom of snakes genus Atractaspis, structurally and pharmacologically near to endothelins. The current minireview focuses on the chemical and molecular aspects of endothelins and sarafotoxins, and their receptors in physiological and pathophysiological processes.

The Role of β-Adrenergic Overstimulation in the Early Stages of Renal Injury

BACKGROUND/AIMS

To assess the possible contribution of the β-adrenergic overstimulation in early stages of renal injury, the present study evaluated, in rats, the effects of the β-adrenoceptor agonist isoproterenol (ISO) on renal function and morphology, as well as the renal mRNA and protein expression of the NADPH oxidase isoform 4 (Nox 4) and subunit p22phox, endoplasmic reticulum (ER) stress, pro-inflammatory, pro-apoptotic and renin-angiotensin system (RAS) components.

METHODS

Wistar rats received ISO (0.3 mg.kg-1.day-1 s.c.) or vehicle (control) for eight days. At the end of the treatment, food and water intake, urine output and body weight gain were evaluated and renal function studies were performed. Renal tissue was used for the morphological, quantitative PCR and immunohistochemical studies.

RESULTS

ISO did not change metabolic parameters or urine output. However it induced a decrease in renal blood flow and an increase in the filtration fraction. These changes were accompanied by increased cortical mRNA and protein expression for the renal oxidative stress components including Nox 4 and p22phox; ER stress, pro-inflamatory, pro-apoptotic as well as RAS components. ISO also induced a significant increase in medullar renin protein expression.

CONCLUSION

These findings support relevant information regarding the contribution of specific β-adrenergic hyperactivity in early stage of renal injury, indicating the reactive oxygen species, ER stress and intrarenal RAS as important factors in this process.

Physiological Changes to the Cardiovascular System at High Altitude and Its Effects on Cardiovascular Disease

Riley, Callum James, and Matthew Gavin. Physiological changes to the cardiovascular system at high altitude and its effects on cardiovascular disease. High Alt Med Biol. 18:102-113, 2017.-The physiological changes to the cardiovascular system in response to the high altitude environment are well understood. More recently, we have begun to understand how these changes may affect and cause detriment to cardiovascular disease. In addition to this, the increasing availability of altitude simulation has dramatically improved our understanding of the physiology of high altitude. This has allowed further study on the effect of altitude in those with cardiovascular disease in a safe and controlled environment as well as in healthy individuals. Using a thorough PubMed search, this review aims to integrate recent advances in cardiovascular physiology at altitude with previous understanding, as well as its potential implications on cardiovascular disease. Altogether, it was found that the changes at altitude to cardiovascular physiology are profound enough to have a noteworthy effect on many forms of cardiovascular disease. While often asymptomatic, there is some risk in high altitude exposure for individuals with certain cardiovascular diseases. Although controlled research in patients with cardiovascular disease was largely lacking, meaning firm conclusions cannot be drawn, these risks should be a consideration to both the individual and their physician.

Simulation of cell-substrate traction force dynamics in response to soluble factors

Finite element (FE) simulations of contractile responses of vascular muscular thin films (vMTFs) and endothelial cells resting on an array of microposts under stimulation of soluble factors were conducted in comparison with experimental measurements reported in the literature. Two types of constitutive models were employed in the simulations, i.e. smooth muscle cell type and non-smooth muscle cell type. The time histories of the effects of soluble factors were obtained via calibration against experimental measurements of contractile responses of tissues or cells. The numerical results for vMTFs with micropatterned tissues suggest that the radius of curvature of vMTFs under stimulation of soluble factors is sensitive to width of the micropatterned tissue, i.e. the radius of curvature increases as the tissue width decreases. However, as the tissue response is essentially isometric, the time history of the maximum principal stress of the micropatterned tissues is not sensitive to tissue width. Good agreement has been achieved for predictions of the vasoconstrictor endothelin-1-induced contraction stress between the FE numerical simulation and the experiment-based approach of Alford (Integr Biol 3:1063-1070, 2011) for the vMTFs with 40, 60, 80 and 100 [Formula: see text] width patterns. This may suggest the contraction stress is weakly sensitive to the tissue width for these patterns. However, for 20 [Formula: see text] width tissue patterning, the numerical simulation result for contraction stress is less than the average value of experimental measurements, which may suggest the thinner and more elongated spindle-like cells within the 20 [Formula: see text] width tissue patterning have higher contractile output. The constitutive model for non-smooth muscle cells was used to simulate the contractile response of the endothelial cells. The substrate was treated as an effective continuum. For agonists such as lysophosphatidic acid and vascular endothelial growth factor, the deformation of the cell diminishes from edge to centre and the central part of the cell is essentially under isometric state. Numerical studies demonstrated the scenarios that cell polarity can be triggered via manipulation of the effective stiffness and Possion's ratio of the substrate.

Endothelin-1 contributes to the progression of renal injury in sickle cell disease via reactive oxygen species

BACKGROUND AND PURPOSE

Endothelin-1 (ET-1) is increased in patients with sickle cell disease and may contribute to the development of sickle cell nephropathy. The current study was designed to determine whether ET-1 acting via the ETA receptor contributes to renal injury in a mouse model of sickle cell disease.

EXPERIMENTAL APPROACH

Adult, humanized HbSS (homozygous for sickle Hb) mice had increased ET-1 mRNA expression in both the cortex and the glomeruli compared with mice heterozygous for sickle and Hb A (HbAS controls). In the renal cortex, ETA receptor mRNA expression was also elevated in HbSS (sickle) mice although ETB receptor mRNA expression was unchanged. Ligand binding assays confirmed that sickle mice had increased ETA receptors in the renal vascular tissue when compared with control mice.

KEY RESULTS

In response to PKC stimulation, reactive oxygen species production by isolated glomeruli from HbSS sickle mice was increased compared with that from HbSA controls, an effect that was prevented by 1 week in vivo treatment with the selective ETA antagonist, ABT-627. Protein and nephrin excretion were both elevated in sickle mice, effects that were also significantly attenuated by ABT-627. Finally, ETA receptor antagonism caused a significant reduction in mRNA expression of NADPH oxidase subunits, which may contribute to nephropathy in sickle cell disease.

CONCLUSIONS AND IMPLICATIONS

These data support a novel role for ET-1 in the progression of sickle nephropathy, specifically via the ETA receptor, and suggest a potential role for ETA receptor antagonism in a treatment strategy.

Dual inhibition of renin-angiotensin-aldosterone system and endothelin-1 in treatment of chronic kidney disease

Inhibition of the renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in treatment of chronic kidney diseases (CKD). However, reversal of the course of CKD or at least long-term stabilization of renal function are often difficult to achieve, and many patients still progress to end-stage renal disease. New treatments are needed to enhance protective actions of RAAS inhibitors (RAASis), such as angiotensin-converting enzyme (ACE) inhibitors (ACEIs) or angiotensin receptor blockers (ARBs), and improve prognosis in CKD patients. Inhibition of endothelin (ET) system in combination with established RAASis may represent such an approach. There are complex interactions between both systems and similarities in their renal physiological and pathophysiological actions that provide theoretical rationale for combined inhibition. This view is supported by some experimental studies in models of both diabetic and nondiabetic CKD showing that a combination of RAASis with ET receptor antagonists (ERAs) ameliorate proteinuria, renal structural changes, and molecular markers of glomerulosclerosis, renal fibrosis, or inflammation more effectively than RAASis or ERAs alone. Practically all clinical studies exploring the effects of RAASis and ERAs combination in nephroprotection have thus far applied add-on designs, in which an ERA is added to baseline treatment with ACEIs or ARBs. These studies, conducted mostly in patients with diabetic nephropathy, have shown that ERAs effectively reduce residual proteinuria in patients with baseline RAASis treatment. Long-term studies are currently being conducted to determine whether promising antiproteinuric effects of the dual blockade will be translated in long-term nephroprotection with acceptable safety profile.

Exposure to fipronil elevates systolic blood pressure and disturbs related biomarkers in plasma of rats

Recent reports show that fipronil affects non-target organisms, including environmental species populations and potentially humans. We aimed to examine if fipronil exposure affects the systolic blood pressure and related biomarkers. Thus, fipronil was orally administered to rats (30 mg/kg/day) during 15 days (Fipronil group) or physiological solution (Control group). While fipronil increased significantly the systolic blood pressure (158±13 mmHg), no significant changes were observed in Control group (127±3 mmHg). Significantly, higher levels of fipronil in plasma were observed in Fipronil group (0.46±0.09 μg/mL versus 0.17±0.11 μg/mL in Control group). Fipronil group showed lower weight gain compared with Control group. While fipronil resulted in higher concentrations of endothelin-1, reduced antioxidant capacity and lower levels of circulating matrix metalloproteinase 2 (MMP-2) and nitric oxide (NO) metabolites compared to Control group, no alteration was observed in serum biomarkers of renal and hepatic/biliary functional abilities. Therefore, this study suggests that fipronil causes hypertension and endothelin-1 plays a key role. Also, these findings suggest that reductions of both MMP-2 and NO may contribute with the elevation of systolic blood pressure observed with fipronil.

Methamphetamine induces the release of endothelin

Methamphetamine is a potent psychostimulant drug of abuse that increases release and blocks reuptake of dopamine, producing intense euphoria, factors that may contribute to its widespread abuse. It also produces severe neurotoxicity resulting from oxidative stress, DNA damage, blood-brain barrier disruption, microgliosis, and mitochondrial dysfunction. Intracerebral hemorrhagic and ischemic stroke have been reported after intravenous and oral abuse of methamphetamine. Several studies have shown that methamphetamine causes vasoconstriction of vessels. This study investigates the effect of methamphetamine on endothelin-1 (ET-1) release in mouse brain endothelial cells by ELISA. ET-1 transcription as well as endothelial nitric oxide synthase (eNOS) activation and transcription were measured following methamphetamine treatment. We also examine the effect of methamphetamine on isolated cerebral arteriolar vessels from C57BL/6 mice. Penetrating middle cerebral arterioles were cannulated at both ends with a micropipette system. Methamphetamine was applied extraluminally, and the vascular response was investigated. Methamphetamine treatment of mouse brain endothelial cells resulted in ET-1 release and a transient increase in ET-1 message. The activity and transcription of eNOS were only slightly enhanced after 24 hr of treatment with methamphetamine. In addition, methamphetamine caused significant vasoconstriction of isolated mouse intracerebral arterioles. The vasoconstrictive effect of methamphetamine was attenuated by coapplication of the endothelin receptor antagonist PD145065. These findings suggest that vasoconstriction induced by methamphetamine is mediated through the endothelin receptor and may involve an endothelin-dependent pathway.

ET-1 mediates the release of reactive oxygen species and TNF-α in lung tissue by protein kinase C α and β1

BACKGROUND

The aim of this study was to determine the involvement of protein kinase C (PKC) in the ET-1 induced generation of reactive oxygen species and TNF-α in rat lungs.

METHODS

Experiments were performed on 6 groups of rats: Group I: saline-treated control; Group II: saline followed by endothelin-1 (ET-1) (3μg/kg); Group III: saline followed by selective PKC αβ1 inhibitor (Gö6976) (2μg/kg); Group IV: Gö6976 (2μg/kg) administered 30min before ET-1 (3μg/kg); Group V: saline followed by the PKC activator phorbol 12-myristate 13-acetate (PMA) (50μg/kg); Group VI: Gö6976 (2μg/kg) administered 30min before PMA (50μg/kg). After 5h, the animals were euthanized and their lungs were isolated for measurements.

RESULTS

ET-1 resulted in increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H2O2) levels and lung edema, as well as a decrease in GSH/GSSG ratio compared to the controls. The level of TNF-α also was elevated in the presence of ET-1. Administration of Gö6976 30min before ET-1 injection significantly decreased lung edema, as well as the concentrations of TBARS, H2O2 and TNF-α, but increased the GSH/GSSG redox ratio compared to ET-1. Conversely, PMA elevated lung edema and TBARS, H2O2 and TNF-α concentrations, but decreased the GSH/GSSG redox ratio compared to the control group. Treatment with Gö6976 significantly ameliorated the PMA-induced oxidative stress parameters, decreased tissue TNF-α level, and lung edema.

CONCLUSION

Endothelin-1 induces ROS generation, increases TNF-α level and lung edema via activation of PKC αβ1.

Bosentan normalizes the GFR response to renal nerve stimulation following reversible unilateral ureteric obstruction in the rat

We investigated the renal response to direct renal nerve stimulation, 2 weeks following reversal of 24-h unilateral (left) ureteric obstruction. Renal nerve stimulation caused a 13-15 % fall in renal blood flow, in 4 groups of anesthetized rats following ureteric obstruction (n=9) or a sham operation (n=7) both with (n=9) and without (n=7) treatment with the mixed ET(A/B) receptor antagonist, bosentan. In the sham-operated rats, renal nerve stimulation did not change glomerular filtration rate but reduced urine flow rate (37+/-3 %, P<0.001), and absolute (38+/-4 %, P<0.001) and fractional (35+/-5 %, P<0.01) sodium excretion. Following unilateral ureteric obstruction, renal nerve stimulation increased glomerular filtration rate by 22+/-3 % (P<0.01), but reduced urine flow rate (14+/-2 %, P<0.001) and fractional sodium excretion (23+/-5 %, P<0.01). Bosentan treatment had no effect on baseline or renal responses to renal nerve stimulation in the sham group but normalized the renal response to renal nerve stimulation in the unilateral ureteric obstruction group. We conclude that 14 days after a 24-h period of unilateral ureteric obstruction there is an increase in GFR in response to direct renal nerve stimulation, which is due, in part, to the actions of endothelin at the time of obstruction.

Linking the beneficial effects of current therapeutic approaches in diabetes to the vascular endothelin system

The rising epidemic of diabetes worldwide is of significant concern. Although the ultimate objective is to prevent the development and find a cure for the disease, prevention and treatment of diabetic complications is very important. Vascular complications in diabetes, or diabetic vasculopathy, include macro- and microvascular dysfunction and represent the principal cause of morbidity and mortality in diabetic patients. Endothelial dysfunction plays a pivotal role in the development and progression of diabetic vasculopathy. Endothelin-1 (ET-1), an endothelial cell-derived peptide, is a potent vasoconstrictor with mitogenic, pro-oxidative and pro-inflammatory properties that are particularly relevant to the pathophysiology of diabetic vasculopathy. Overproduction of ET-1 is reported in patients and animal models of diabetes and the functional effects of ET-1 and its receptors are also greatly altered in diabetic conditions. The current therapeutic approaches in diabetes include glucose lowering, sensitization to insulin, reduction of fatty acids and vasculoprotective therapies. However, whether and how these therapeutic approaches affect the ET-1 system remain poorly understood. Accordingly, in the present review, we will focus on experimental and clinical evidence that indicates a role for ET-1 in diabetic vasculopathy and on the effects of current therapeutic approaches in diabetes on the vascular ET-1 system.

Spironolactone rescues Dot1a-Af9-mediated repression of endothelin-1 and improves kidney injury in streptozotocin-induced diabetic rats

The molecular mechanism linking aldosterone and endothelin-1 in the development of diabetic nephropathy has not been completely elucidated. Here, we provide evidence showing that streptozotocin-induced diabetic rats have significantly increased aldosterone and endothelin-1 in the kidney tissue and markedly decreased expression of Dot1a and Af9. Blocking aldosterone with spironolactone significantly reduced proteinuria, glomerulosclerosis, tubulointerstitial injury and endothelin-1 expression, and significantly increased Dot1a and Af9 expression. Increasing Dot1a and Af9 expression by spironolactone or by stable transfection led to impaired endothelin-1 expression in NRK-52 cells. In contrast, downregulation of Dot1a and Af9 by aldosterone in NRK-52E cells caused upregulation of endothelin-1. Genetic inactivation of Dot1l, which encodes Dot1a, in Aqp2-expressing principal cells of mouse kidney impaired association of Dot1a and H3 dimethyl K79 with the specific subregions of endothelin-1 promoter, and upregulates endothelin-1 mRNA and protein expression. Our data suggest that Dot1a and Af9 repress endothelin-1 in vitro and in vivo. Excessive aldosterone induces kidney injury, in part possibly by downregulating Dot1a and Af9, and thus relieving Dot1a-Af9-mediated repression to increase endothelin-1 transcription. Spironolactone ameliorates kidney injury in Streptozotocin-induced diabetic rats, possibly by restoring Dot1a-Af9-mediated repression to reduce endothelin-1 expression. Therefore, Dot1a and Af9 as aldosterone-downregulated targets are negative regulators of endothelin-1 transcription in vitro and in vivo, and may be considered as new potential therapeutic targets of kidney injury in diabetes.

Possible bi-directional link between ET(A) receptors and protein kinase C in rat blood vessels

Possible links have been investigated between activation of protein kinase C (PKC) and endothelin (ET) production by small blood vessels. Perfusion pressures were recorded from rat isolated mesenteric artery, with or without the small intestine attached, before and after addition to the perfusate of either ET-1, ET-3 or the PKC activator 12-deoxyphorbol 13-phenylacetate (DOPPA). Rises in perfusion pressure in response to ET-1 (10⁻⁸ M)or DOPPA (10⁻⁶ M) were reduced significantly by pre-treatment with either the ET_A receptor antagonist PD151242 (10⁻⁶ M) or the PKC inhibitor Ro 31-8220 (10⁻⁶ M). ET-3 (10⁻⁸ M) had a significant, albeit small, effect only when the gut was still attached to the mesentery. Inthis latter preparation ET-1 and DOPPA increased the permeability of villi microvessels to colloidal carbon in the perfusate. This effect of DOPPA was reduced by pre-treatment with either PD151242 or Ro 31-8220, but the effects of ET-1 were reduced significantly only by Ro 31-8220. ET-3 (10⁻⁸ M) was without effect. The results suggest a possible bi-directional link between ET_A receptors and PKC in the intestinal vasculature.

Novel regulation of endothelin-1 promoter activity by protein kinase C

Endothelin-1 (ET-1) is produced in unusually large amounts by the renal collecting duct and acts locally to control renal salt and water excretion and arterial pressure; disorders of collecting duct ET-1 activity can cause marked hypertension. The mechanisms regulating collecting duct ET-1 synthesis are, however, poorly understood. In this study, we investigated the role of protein kinase C (PKC), a known regulator of ET-1 production in endothelial cells, in (1) the control of collecting duct ET-1 production; and (2) the modulation of ET-1 promoter region activity. Cultured rat inner medullary collecting duct (IMCD) cells were studied. Calphostin C, a PKC inhibitor, greatly reduced IMCD ET-1 release. Sustained exposure to phorbol myristate acetate (PMA) also decreased ET-1 secretion. PKC inhibition decreased steady-state ET-1 mRNA content. A brief exposure (15 min) to PMA augmented ET-1 mRNA levels, while prolonged PMA exposure (120 min) reduced ET-1 mRNA content, PKC inhibition did not affect ET-1 mRNA stability. Transfection of ET-1 promoter-luciferase reporter constructs into IMCD cells demonstrated that PKC inhibition reduced activity of only the larger promoter fragments (containing at least 1,725 bp 5' to the ET-1 gene transcription start site). Mutation of a previously identified AP-1 site at -186 in the ET-1 promoter greatly reduced activity of transfected ET-1 promoter-reporter constructs (containing 366 or 1,725 bp 5' to the transcription start site); however, this region appears not to be regulated by PKC in IMCD cells. In summary, PKC stimulates collecting duct ET-1 synthesis via transcriptional activation of the ET-1 promoter. Such transcriptional activation occurs at a heretofore undescribed PKC-regulated region of the ET-1 promoter.

TRC120038, a Novel Dual AT(1)/ET(A) Receptor Blocker for Control of Hypertension, Diabetic Nephropathy, and Cardiomyopathy in ob-ZSF1 Rats

In hypertensive subjects, angiotensin II and endothelin participate in a manner involving closely interwoven pathways in increasing blood pressure (BP) and inducing end organ damage. The primary objective of this study was to determine the effect of TRC120038, a novel dual AT₁/ET_A receptor blocker on BP, in obese Zucker spontaneously hypertensive fatty rats (ob-ZSF1), an animal model of moderate hypertension, diabetes with progressive renal and cardiac dysfunction. Ob-ZSF1 rats loaded with 0.5% salt were treated with TRC120038 (11.8 mg/kg bid.) or candesartan cilexetil (0.3 mg/kg od.) or vehicle control. Blood pressure (by radio-telemetry) and renal functional markers were monitored throughout the study. Cardiac function was assessed terminally by pressure volume catheter. Markers for renal dysfunction were measured and changes were evaluated histopathologically. TRC120038 showed greater fall in both systolic and diastolic BP in comparison to candesartan at its maximum antihypertensive dose. TRC120038 also reduced the severity of renal dysfunction and preserved cardiac function in ob-ZSF1 rat.

Changes critical to persistent lowering of arterial pressure in spontaneously hypertensive rat occur early in antihypertensive treatment

OBJECTIVES

Angiotensin-converting enzyme inhibition (ACEI) in adult spontaneously hypertensive rats (SHRs) produces reductions in mean arterial pressure (MAP) and vascular structure that persist after treatment cessation. This study used an intermittent treatment strategy to determine the time course of changes in MAP, vascular resistance properties, and the tissue levels of endothelin.

METHODS

Adult SHRs were treated with enalapril and low sodium diet for three 2-week treatment cycles, each separated by 2-week washout periods. MAP was measured via radiotelemetry. Hindlimb structurally based vascular resistance properties were assessed after two treatment cycles. Endothelin was measured in mesenteric vessels, renal cortex and medulla in untreated SHR (Con), and at day 10 of the first and third treatment cycles.

RESULTS

Treatment produced a persistent reduction in MAP; however, the magnitude of change in the 'off-treatment' level decreased following successive treatments (cycle 1: -15 ± 1.7%, cycle 2: -8 ± 1.9%, and cycle 3: -1 ± 1.7%). Reduction in hindlimb vascular structure after two cycles of treatment was not different from that previously observed after one cycle. Endothelin levels were significantly elevated during the third cycle in renal medulla (Con: 797 ± 102 pg/g tissue, cycle 1: 767 ± 81 pg/g tissue, cycle 3: 1097 ± 205 pg/g tissue) and mesenteric vessels (Con: 711 ± 226 pg/g tissue, cycle 1: 696 ± 231 pg/g tissue, cycle 3: 1063 ± 741 pg/g tissue). Concomitant treatment with an endothelin antagonist did not impact arterial pressure.

CONCLUSION

These findings demonstrate that during ACEI treatment, most of the changes that confer persistent changes in MAP and vascular structure occur within the first 2 weeks. Elevation in endothelin levels is likely unrelated to arterial pressure.

Physiology of endothelin and the kidney

Since its discovery in 1988 as an endothelial cell-derived peptide that exerts the most potent vasoconstriction of any known endogenous compound, endothelin (ET) has emerged as an important regulator of renal physiology and pathophysiology. This review focuses on how the ET system impacts renal function in health; it is apparent that ET regulates multiple aspects of kidney function. These include modulation of glomerular filtration rate and renal blood flow, control of renin release, and regulation of transport of sodium, water, protons, and bicarbonate. These effects are exerted through ET interactions with almost every cell type in the kidney, including mesangial cells, podocytes, endothelium, vascular smooth muscle, every section of the nephron, and renal nerves. In addition, while not the subject of the current review, ET can also indirectly affect renal function through modulation of extrarenal systems, including the vasculature, nervous system, adrenal gland, circulating hormones, and the heart. As will become apparent, these pleiotropic effects of ET are of fundamental physiologic importance in the control of renal function in health. In addition, to help put these effects into perspective, we will also discuss, albeit to a relatively limited extent, how alterations in the ET system can contribute to hypertension and kidney disease.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Short-term angiotensin-1 receptor antagonism in type 2 diabetic Goto-Kakizaki rats normalizes endothelin-1-induced mesenteric artery contraction

Endothelin (ET)-1 and angiotensin II (Ang II) are likely candidates for a key role in diabetic vascular complications. We demonstrated previously that an enhanced ET-1-induced contraction is present in mesenteric arteries from Goto-Kakizaki (GK) rats at the chronic stage of type 2 diabetes. Here, we investigated whether short-term treatment of such rats with losartan, an angiotensin type 1 receptor antagonist, might normalize the ET-1-induced contraction. In mesenteric arteries from GK rats at the chronic stage (34-38 weeks) (vs. those from age-matched control Wistar rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of ET-1 and Ang II were increased, (3) ET-1-stimulated ERK2 phosphorylation was increased, and (4) the ACh-induced endothelium-dependent relaxation was reduced. Mesenteric arteries isolated from such GK rats following treatment with losartan (25mg/kg/day for 2 weeks) exhibited reduced ET-1- and Ang II-induced contractions, suppressed ET-1-stimulated ERK phosphorylation, and increased ACh-induced relaxation, while the rats exhibited normalized plasma NO metabolism and their mesenteric arteries exhibited increased basal NO formation. However, such losartan treatment did not alter the increased levels of ET-1 and Ang II seen in GK mesenteric arteries. Our data suggest that within the timescale studied here, losartan normalizes ET-1-induced mesenteric artery contraction through a suppression of ERK activities and/or by normalizing endothelial function.

Effect of Systemic Insulin and Angiotensin II Receptor Subtype-1 Antagonist on Endothelin-1 Receptor Subtype(s) Regulation and Binding in Diabetic Rat Heart

This study reports on the regulation and remodeling role of endothelin-1 (ET-1) and its receptor subtypes, ET(A)-Rs/ET(B)-Rs, at the coronary endothelium (CE) and cardiomyocyte (CM) sites. It is carried out in normal and normotensive rats with streptozotocin-induced diabetes mellitus receiving different treatment modalities. Normal rats were divided into two groups, namely a placebo (N) and a losartan-treated (NL), and diabetic rats into four groups receiving placebo (D), insulin-treated (DI), losartan-treated (DL), and insulin/losartan-treated (DIL) respectively. Binding kinetics of ET-1 to ET(A)-Rs/ET(B)-Rs on CE and CMs were assessed in the above groups to try to explain the effect of therapeutic doses of an angiotensin II receptor subtype-1 blocker on the dynamics of this ligand and its receptor in insulin supplemented diabetic animals. Each group was divided into two subgroups: CHAPS-untreated and CHAPS-treated rat hearts perfused with [125I]ET-1 to respectively estimate ET-1 binding affinity (tau = 1/k-n) to its receptor subtype(s) on CE and CMs using mathematical modeling describing a 1:1 reversible binding stoichiometry. Heart perfusion results revealed that insulin treatment significantly decreased tau on CE but not on CMs in diabetic rats. In diabetics treated with losartan, an increase in tau value on CE but not on CMs was noted. Cotreatment of diabetic rats with insulin and losartan normalized tau on CE but decreased it on CMs. Western blot, using snap-frozen heart tissues, revealed increase in ET(A)-R density in all diabetic groups. However, significant decrease in ET(B)-R density was observed in all groups compared to the normal, and was reconfirmed by immunohistochemical analysis. In conclusion, coadministration of insulin and losartan in nonhypertensive animals suffering from diabetes type 1 may offer new cardiac protection benefits by improving coronary blood flow and cardiomyocyte contractility through modulating ET-1 receptor subtypes density and affinity at CE and CM sites.

Raised Plasma Concentrations of Endothelin-1 and -3 in Marmosets with Acute Aortic Stenosis: No Relation to the Renin-angiotensin System

Plasma levels of endothelin (ET), plasma renin activity (PRA) and angiotensin II (Ang II) were measured in anaesthetized marmosets exposed to acute aortic stenosis proximal to the renal arteries. In vehicle experiments, ET rose from 5 +/- 2 to 38 +/- 4 pg ml-1, PRA from 5 +/- 2 to 99 +/- 21 ng ml-1 h-1 and Ang II from 21 +/- 4 to 213 +/- 76 pg ml-1. Administration of renin inhibitor and angiotensin converting enzyme inhibitor reduced PRA and Ang II to control levels, while the plasma levels of ET increased further (51 +/- 10 and 71 +/- 16 pg ml-1, respectively). During aortic stenosis the two isoforms ET-1 and ET-3 appeared in the circulation, while in conscious control animals only ET-1 was found. It is concluded that the increased plasma levels of ET in our primate model could not be ascribed to the increased circulating levels of PRA and Ang II.

Ambrisentan for the treatment of pulmonary arterial hypertension

Ambrisentan is an endothelin receptor antagonist (ERA) that was recently approved for treatment of pulmonary arterial hypertension (PAH). Endothelin (ET) is a potent vasoconstrictor with mitogenic, hypertrophic and pro-inflammatory properties that is upregulated in pulmonary hypertensive diseases. The biologic effects of ET are mediated by 2 cell surface receptors termed ET_A and ET_B. ET_A mediates the vasoconstrictor effect of ET on vascular smooth muscle, whereas ET_B is expressed primarily on vascular endothelial cells where it induces nitric oxide synthesis and acts to clear ET from the circulation. Ambrisentan is the first ET_A selective ERA approved for use in the US. Recently published clinical trials in patients with PAH demonstrate improvement in functional capacity and pulmonary hemodynamics similar to other ET_A selective and non-selective ERAs. Its once daily dosing and lower incidence of serum aminotransferase elevation offer potential advantages over other ERAs, but further experience with this agent is needed to fully understand its long-term efficacy and safety. This review discusses the endothelin family of proteins and receptors and their role in the pathophysiology of pulmonary hypertensive diseases. It also examines the development process, safety profile and clinical trials that have resulted in ambrisentan being approved for treatment of PAH.

Arginine vasopressin in the treatment of vasodilatory septic shock

Vasodilatory septic shock is characterized by profound vasodilation of the peripheral circulation, relative refractoriness to catecholamines and a relative deficiency of the posterior pituitary hormone, vasopressin. Arginine vasopressin is effective in restoring vascular tone in vasodilatory septic shock and may be associated with decreased mortality in less severe septic shock as well as improved mortality and decreased renal failure in septic shock patients at risk for renal failure.

Expression of human endothelin-converting enzyme isoforms: role of angiotensin II

A key step in endothelin-1 (ET-1) synthesis is the proteolytic cleavage of big ET-1 by the endothelin-converting enzyme-1 (ECE-1). Four alternatively spliced isoforms, ECE-1a to ECE-1d, have been discovered; however, regulation of the expression of specific ECE-1 isoforms is not well understood. Therefore, we stimulated primary human umbilical vein endothelial cells (HUVECs) with angiotensin II (Ang II). Furthermore, expression of ECE-1 isoforms was determined in internal mammary arteries of patients undergoing coronary artery bypass grafting surgery. Patients had received one of 4 therapies: angiotensin-converting enzyme inhibitors (ACE-I), Ang II type 1 receptor blockers (ARB), HMG-CoA reductase inhibitors (statins), and a control group that had received neither ACE-I, ARB (that is, treatment not interfering in the renin-angiotensin system), nor statins. Under control conditions, ECE-1a is the dominant isoform in HUVECs (4.5+/-2.8 amol/microg RNA), followed by ECE-1c (2.7+/-1.0 amol/microg), ECE-1d (0.49+/-0.17 amol/microg), and ECE-1b (0.17+/-0.04 amol/microg). Stimulation with Ang II did not change the ECE-1 expression pattern or the ET-1 release. We found that ECE-1 mRNA expression was higher in patients treated with statins than in patients treated with ARB therapy (5.8+/-0.76 RU versus 3.0+/-0.4 RU), mainly attributed to ECE-1a. In addition, ECE-1a mRNA expression was higher in patients receiving ACE-I therapy than in patients receiving ARB therapy (1.68+/-0.27 RU versus 0.83+/-0.07 RU). We conclude that ECE-1a is the major ECE-1 isoform in primary human endothelial cells. Its expression in internal mammary arteries can be regulated by statin therapy and differs between patients with ACE-I and ARB therapy.

Renin: at the heart of the mast cell

Cardiac mast cells proliferate in cardiovascular diseases. In myocardial ischemia, mast cell mediators contribute to coronary vasoconstriction, arrhythmias, leukocyte recruitment, and tissue injury and repair. Arrhythmic dysfunction, coronary vasoconstriction, and contractile failure are also characteristic of cardiac anaphylaxis. In coronary atherosclerosis, mast cell mediators facilitate cholesterol accumulation and plaque destabilization. In cardiac failure, mast cell chymase causes myocyte apoptosis and fibroblast proliferation, leading to ventricular dysfunction. Chymase and tryptase also contribute to fibrosis in cardiomyopathies and myocarditis. In addition, mast cell tumor necrosis factor-alpha promotes myocardial remodeling. Cardiac remodeling and hypertrophy in end-stage hypertension are also induced by mast cell mediators and proteases. We recently discovered that cardiac mast cells contain and release renin, which initiates local angiotensin formation. Angiotensin causes coronary vasoconstriction, arrhythmias, fibrosis, apoptosis, and endothelin release, all demonstrated mechanisms of mast-cell-associated cardiac disease. The effects of angiotensin are further amplified by the release of norepinephrine from cardiac sympathetic nerves. Our discovery of renin in cardiac mast cells and its release in pathophysiological conditions uncovers an important new pathway in the development of mast-cell-associated heart diseases. Several steps in this novel pathway may constitute future therapeutic targets.

Vasopressin: mechanisms of action on the vasculature in health and in septic shock

BACKGROUND

Vasopressin is essential for cardiovascular homeostasis, acting via the kidney to regulate water resorption, on the vasculature to regulate smooth muscle tone, and as a central neurotransmitter, modulating brainstem autonomic function. Although it is released in response to stress or shock states, a relative deficiency of vasopressin has been found in prolonged vasodilatory shock, such as is seen in severe sepsis. In this circumstance, exogenous vasopressin has marked vasopressor effects, even at doses that would not affect blood pressure in healthy individuals. These two findings provide the rationale for the use of vasopressin in the treatment of septic shock. However, despite considerable research attention, the mechanisms for vasopressin deficiency and hypersensitivity in vasodilatory shock remain unclear.

OBJECTIVE

To summarize vasopressin's synthesis, physiologic roles, and regulation and then review the literature describing its vascular receptors and downstream signaling pathways. A discussion of potential mechanisms underlying vasopressin hypersensitivity in septic shock follows, with reference to relevant clinical, in vivo, and in vitro experimental evidence.

DATA SOURCE

Search of the PubMed database (keywords: vasopressin and receptors and/or sepsis or septic shock) for articles published in English before May 2006 and manual review of article bibliographies.

DATA SYNTHESIS AND CONCLUSIONS

The pathophysiologic mechanism underlying vasopressin hypersensitivity in septic shock is probably multifactorial. It is doubtful that this phenomenon is merely the consequence of replacing a deficiency. Changes in vascular receptors or their signaling and/or interactions between vasopressin, nitric oxide, and adenosine triphosphate-dependent potassium channels are likely to be relevant. Further translational research is required to improve our understanding and direct appropriate educated clinical use of vasopressin.

Endothelin receptor antagonists

Endothelin receptor antagonists (ERAs) have been developed to block the effects of endothelin-1 (ET-1) in a variety of cardiovascular conditions. ET-1 is a powerful vasoconstrictor with mitogenic or co-mitogenic properties, which acts through the stimulation of 2 subtypes of receptors [endothelin receptor subtype A (ETA) and endothelin receptor subtype B (ETB) receptors]. Endogenous ET-1 is involved in a variety of conditions including systemic and pulmonary hypertension (PH), congestive heart failure (CHF), vascular remodeling (restenosis, atherosclerosis), renal failure, cancer, and cerebrovascular disease. The first dual ETA/ETB receptor blocker, bosentan, has already been approved by the Food and Drug Administration for the treatment of pulmonary arterial hypertension (PAH). Trials of endothelin receptor antagonists in heart failure have been completed with mixed results so far. Studies are ongoing on the effects of selective ETA antagonists or dual ETA/ETB antagonists in lung fibrosis, cancer, and subarachnoid hemorrhage. While non-peptidic ET-1 receptor antagonists suitable for oral intake with excellent bioavailability have become available, proven efficacy is limited to pulmonary hypertension, but it is possible that these agents might find a place in the treatment of several cardiovascular and non-cardiovascular diseases in the coming future.

Increased vascular angiotensin II binding capacity and ET-1 release in young cardiomyopathic hamsters

Heart failure (HF) is a multifactorial and progressive disease that has been associated with multiple systemic and vascular alterations. Previous reports from our laboratory showed that in 2-month-old Bio-To2 Syrian cardiomyopathic hamsters (SCH) that have not yet developed the clinical manifestations of HF, the vascular contractility induced by 0.1 microM angiotensin II was approximately 35% greater than in control animals. This finding was observed concomitantly with an increased aortic ACE activity. To further evaluate the mechanisms underlying angiotensin II-enhanced vascular contraction, concentration-response curves for angiotensin II (0.01 nM-10 microM) were constructed before and after the addition of prazosin (alpha-1 blocker), NS-398 (selective COX-2 blocker) and BQ-123 (ET-1A-receptor antagonist) in aortic rings from 2-month-old SCH. The binding capacity and affinity of the AT-1 receptors were also evaluated in aortic homogenates using 125I-angiotensin II. Age-matched golden hamsters were used as controls (CT). Our results indicate that incubation with either 10 microM prazosin or 10 microM NS-398 did not modify EC50 or Emax values for angiotensin II indicating that norepinephrine and prostaglandins are not involved in the enhanced contractile action of angiotensin II. However, 10 microM BQ-123 reduced by 40% the contraction induced by 1.0 microM angiotensin II (from 1.05+/-0.04 to 0.6475+/-0.06 g/mg tissue, n = 5, P < 0.05), suggesting that in cardiomyopathic hamsters, the action of angiotensin II is mediated in part by ET-1. At lower angiotensin II concentration (0.1 microM), the ET-1-dependent contraction decreases to 29%. In addition, although dissociation constants for labeled angiotensin II were found to be similar in the aorta of SCH and control animals (K(D): CT = 7.8 nM and SCH = 5.1 nM), 125I-angiotensin II binding capacity was about 2-fold greater in SCH than in controls (Bmax: SCH = 1113 and CT = 605 fmol/mg protein). Altogether these results suggest that in 2-month-old SCH the enhanced response of angiotensin II in the vasculature is mediated both by an increased binding capacity for the hormone and facilitation of the ET-1 action.

Plasma levels of endothelin-1, angiotensin II, nitric oxide and prostaglandin E2 in the venous and cavernosal blood of patients with erectile dysfunction

OBJECTIVES

To determine the alterations in the plasma levels of endothelin-1, angiotensin II, nitric oxide (NO) and prostaglandin E(2) (PGE(2)) in the venous and cavernosal blood of patients with organic and psychogenic erectile dysfunction (ED).

PATIENTS, SUBJECTS AND METHODS

The study included 32 patients complaining of ED; they were subdivided into two equal groups with either organic or psychogenic ED. Fifteen healthy potent age-matched male volunteers were enrolled as a control group. For each patient, venous and cavernosal blood samples were obtained, while venous blood was obtained from the controls.

RESULTS

There were significantly greater mean plasma levels of endothelin-1 and angiotensin II, and significantly lower mean plasma levels of NO and PGE(2), in the venous blood of patients with ED than in the controls. Patients with organic ED had significantly higher levels of endothelin-1 and significantly lower levels of NO in both venous and cavernosal blood than had those with psychogenic ED. There were significant positive correlations in both venous and cavernosal blood between endothelin-1 and angiotensin II, and between NO and PGE(2) in all patients with ED and the two subgroups. There were significant negative correlations between venous and cavernosal endothelin-1 and NO, endothelin-1 and PGE(2), angiotensin II and NO, and between angiotensin II and PGE(2).

CONCLUSION

The present results suggest that endothelin-1 could be a clinical marker of diffuse endothelial disease manifested by ED. As angiotensin-converting enzyme (ACE) activity controls angiotensin II there might be a rationale for the use of ACE inhibitors to prevent or treat ED. NO and PGE(2) may provide new strategies for the pharmacological treatment of ED.

Blood flow: a key regulatory component of corpus luteum function in the cow

Prostaglandin F2alpha (PGF2alpha) is the primary luteolysin in the cow. During the early luteal phase, the corpus luteum (CL) is resistant to the luteolytic effect of PGF2alpha. Once mature, the CL becomes responsive to PGF2alpha and undergoes luteal regression. These actions of PGF2alpha coincide with changes in luteal blood flow (BF): PGF2alpha has no effect on BF in the early CL, but acutely increases BF in the peripheral vasculature of the mature CL within 30 min of PGF2alpha injection. During spontaneous luteolysis, luteal BF increases on Days 17-18 of the estrous cycle, prior to any decrease in plasma progesterone (P). The increase in luteal BF is synchronous with an increase in plasma PGFM levels, suggesting that pulsatile release of PGF2alpha from uterus stimulates the increase in luteal BF. Serial biopsies of these CL showed that mRNA expression for endothelial nitric oxide synthase (eNOS) together with endothelin-1 (ET-1) and angiotensin converting enzyme (ACE) increases on Days 17-18 when the luteal BF is elevated. On Day 19 when plasma P level firstly decreases, eNOS mRNA returns to the basal level whereas ET-1 and ACE mRNA remains elevated. Cyclooxygenase-2 (COX-2) mRNA expression increases on Day 19. In support of these data, an in vivo microdialysis study revealed that luteal ET-1 and angiotensin II (Ang II) secretion increases and precedes PGF2alpha secretion during spontaneous luteolysis. In conclusion, we show for the first time that an acute increase of BF occurs in the peripheral vasculature of the mature CL together with increases in eNOS expression and ET-1 and Ang II secretion in the CL during the early stages of luteolysis in the cow. We propose that the increase in luteal BF may be induced by NO from large arterioles surrounding the CL, and simultaneously uterine or exogenous PGF2alpha directly increases ET-1 and Ang II secretion from endothelial cells of microcapillary vessels within the CL, thereby suppressing P secretion by luteal cells. Taken together, our results indicate that an acute increase in luteal BF occurs as a first step of luteolysis in response to PGF2alpha. Therefore, local BF plays a key role to initiate luteal regression in the cow.