Different contributions of endothelin-A and endothelin-B receptors in the pathogenesis of deoxycorticosterone acetate-salt-induced hypertension in rats

Gestational intermittent hypoxia induces endothelial dysfunction and hypertension in pregnant rats: role of endothelin type B receptor†

Obstructive sleep apnea is a recognized risk factor for gestational hypertension, yet the exact mechanism behind this association remains unclear. Here, we tested the hypothesis that intermittent hypoxia, a hallmark of obstructive sleep apnea, induces gestational hypertension through perturbed endothelin-1 signaling. Pregnant Sprague-Dawley rats were subjected to normoxia (control), mild intermittent hypoxia (10.5% O2), or severe intermittent hypoxia (6.5% O2) from gestational days 10-21. Blood pressure was monitored. Plasma was collected and mesenteric arteries were isolated for myograph and protein analyses. The mild and severe intermittent hypoxia groups demonstrated elevated blood pressure, reduced plasma nitrate/nitrite, and unchanged endothelin-1 levels compared to the control group. Western blot analysis revealed decreased expression of endothelin type B receptor and phosphorylated endothelial nitric oxide synthase, while the levels of endothelin type A receptor and total endothelial nitric oxide synthase remained unchanged following intermittent hypoxia exposure. The contractile responses to potassium chloride, phenylephrine, and endothelin-1 were unaffected in endothelium-denuded arteries from mild and severe intermittent hypoxia rats. However, mild and severe intermittent hypoxia rats exhibited impaired endothelium-dependent vasorelaxation responses to endothelin type B receptor agonist IRL-1620 and acetylcholine compared to controls. Endothelium denudation abolished IRL-1620-induced vasorelaxation, supporting the involvement of endothelium in endothelin type B receptor-mediated relaxation. Treatment with IRL-1620 during intermittent hypoxia exposure significantly attenuated intermittent hypoxia-induced hypertension in pregnant rats. This was associated with elevated circulating nitrate/nitrite levels, enhanced endothelin type B receptor expression, increased endothelial nitric oxide synthase activation, and improved vasodilation responses. Our data suggested that intermittent hypoxia exposure during gestation increases blood pressure in pregnant rats by suppressing endothelin type B receptor-mediated signaling, providing a molecular mechanism linking intermittent hypoxia and gestational hypertension.

Endothelin-1 Induces Cell Proliferation and Myofibroblast Differentiation through the ETAR/Gαq/ERK Signaling Pathway in Human Cardiac Fibroblasts

Endothelin-1 (ET-1) has been implicated in the pathogenesis of cardiac fibrosis. Stimulation of endothelin receptors (ETR) with ET-1 leads to fibroblast activation and myofibroblast differentiation, which is mainly characterized by an overexpression of α-smooth muscle actin (α-SMA) and collagens. Although ET-1 is a potent profibrotic mediator, the signal transductions and subtype specificity of ETR contributing to cell proliferation, as well as α-SMA and collagen I synthesis in human cardiac fibroblasts are not well clarified. This study aimed to evaluate the subtype specificity and signal transduction of ETR on fibroblast activation and myofibroblast differentiation. Treatment with ET-1 induced fibroblast proliferation, and synthesis of myofibroblast markers, α-SMA, and collagen I through the ET_AR subtype. Inhibition of G_αq protein, not G_αi or G_βγ, inhibited these effects of ET-1, indicating the essential role of G_αq protein-mediated ET_AR signaling. In addition, ERK1/2 was required for ET_AR/G_αq axis-induced proliferative capacity and overexpression of these myofibroblast markers. Antagonism of ETR with ETR antagonists (ERAs), ambrisentan and bosentan, inhibited ET-1-induced cell proliferation and synthesis of α-SMA and collagen I. Furthermore, ambrisentan and bosentan promoted the reversal of myofibroblasts after day 3 of treatment, with loss of proliferative ability and a reduction in α-SMA synthesis, confirming the restorative effects of ERAs. This novel work reports on the ET_AR/G_αq/ERK signaling pathway for ET-1 actions and blockade of ETR signaling with ERAs, representing a promising therapeutic strategy for prevention and restoration of ET-1-induced cardiac fibrosis.

Distinct effects of bosentan on NO-dependent vasodilation and calcium influx in heterozygous Ren-2 transgenic rats on high-salt diet

Our studies in hypertensive Ren-2 transgenic rats (TGR) demonstrated that chronic administration of atrasentan (ETA receptor antagonist) decreased blood pressure by reduced Ca2+ influx through L-type voltage-dependent calcium channels (L-VDCC) and attenuated angiotensin II-dependent vasoconstriction. We were interested whether bosentan (nonselective ET(A)/ET(B) receptor antagonist) would have similar effects. Young 4-week-old (preventive study) and adult 8-week-old (therapeutic study) heterozygous TGR and their normotensive Hannover Sprague-Dawley (HanSD) controls were fed normal-salt (NS, 0.6 % NaCl) or high-salt (HS, 2 % NaCl) diet for 8 weeks. An additional group of TGR fed HS was treated with bosentan (100 mg/kg/day). Bosentan had no effect on BP of TGR fed high-salt diet in both the preventive and therapeutic studies. There was no difference in the contribution of angiotensin II-dependent and sympathetic vasoconstriction in bosentan-treated TGR compared to untreated TGR under the condition of high-salt intake. However, bosentan significantly reduced NO-dependent vasodilation and nifedipine-sensitive BP component in TGR on HS diet. A highly important correlation of nifedipine-induced BP change and the BP after L-NAME administration was demonstrated. Although bosentan did not result in any blood pressure lowering effects, it substantially influenced NO-dependent vasodilation and calcium influx through L-VDCC in the heterozygous TGR fed HS diet. A significant correlation of nifedipine-induced BP change and the BP after L-NAME administration suggests an important role of nitric oxide in the closure of L-type voltage dependent calcium channels.

Renoprotective effects of ET(A) receptor antagonists therapy in experimental non-diabetic chronic kidney disease: Is there still hope for the future?

Chronic kidney disease (CKD) is a life-threatening disease arising as a frequent complication of diabetes, obesity and hypertension. Since it is typically undetected for long periods, it often progresses to end-stage renal disease. CKD is characterized by the development of progressive glomerulosclerosis, interstitial fibrosis and tubular atrophy along with a decreased glomerular filtration rate. This is associated with podocyte injury and a progressive rise in proteinuria. As endothelin-1 (ET-1) through the activation of endothelin receptor type A (ET(A)) promotes renal cell injury, inflammation, and fibrosis which finally lead to proteinuria, it is not surprising that ET(A) receptors antagonists have been proven to have beneficial renoprotective effects in both experimental and clinical studies in diabetic and non-diabetic CKD. Unfortunately, fluid retention encountered in large clinical trials in diabetic CKD led to the termination of these studies. Therefore, several advances, including the synthesis of new antagonists with enhanced pharmacological activity, the use of lower doses of ET antagonists, the addition of diuretics, plus simply searching for distinct pathological states to be treated, are promising targets for future experimental studies. In support of these approaches, our group demonstrated in adult subtotally nephrectomized Ren-2 transgenic rats that the addition of a diuretic on top of renin-angiotensin and ET(A) blockade led to a further decrease of proteinuria. This effect was independent of blood pressure which was normalized in all treated groups. Recent data in non-diabetic CKD, therefore, indicate a new potential for ET(A) antagonists, at least under certain pathological conditions.

A novel antihypertension agent, sargachromenol D from marine brown algae, Sargassum siliquastrum, exerts dual action as an L-type Ca2+ channel blocker and endothelin A/B2 receptor antagonist

We isolated the novel vasoactive marine natural products, (5E,10E)-14-hydroxy-2,6,10-trimethylpentadeca-5,10-dien-4-one (4) and sargachromenol D (5), from Sargassum siliquastrum collected from the coast of the East Sea in South Korea by using activity-guided HPLC purification. The compounds effectively dilated depolarization (50mMK+)-induced basilar artery contraction with EC50 values of 3.52±0.42 and 1.62±0.63μM, respectively, but only sargachromenol D (5) showed a vasodilatory effect on endothelin-1 (ET-1)-induced basilar artery contraction (EC50=9.8±0.6μM). These results indicated that sargachromenol D (5) could act as a dual antagonist of l-type Ca2+ channel and endothelin A/B2 receptors. Moreover, sargachromenol D (5) lowered blood pressure in spontaneous hypertensive rats (SHRs) 2h after oral treatment at a dose of 80mg/kg dose and the effect was maintained for 24h. Based on our ex vivo and in vivo experiments, we propose that sargachromenol D (5) is a strong candidate for the treatment of hypertension that is not controlled by conventional drugs, in particular, severe-, type II diabetes-, salt-sensitive, and metabolic disease-induced hypertension.

Animal models for the study of primary and secondary hypertension in humans

Hypertension is a significant cause of morbidity and mortality worldwide. It is defined as systolic and diastolic blood pressures (SBP/DBP) >140 and 90 mmHg, respectively. Individuals with an SBP between 120 and 139, or DBP between 80 and 89 mmHg, are said to exhibit pre-hypertension. Hypertension can have primary or secondary causes. Primary or essential hypertension is a multifactorial disease caused by interacting environmental and polygenic factors. Secondary causes are renovascular hypertension, renal disease, endocrine disorders and other medical conditions. The aim of the present review article was to examine the different animal models that have been generated for studying the molecular and physiological mechanisms underlying hypertension. Their advantages, disadvantages and limitations will be discussed.

Conjugated linoleic acid rat pretreatment reduces renal damage in ischemia/reperfusion injury: Unraveling antiapoptotic mechanisms and regulation of phosphorylated mammalian target of rapamycin

SCOPE

Conjugated linoleic acids (CLAs) are dietary components with beneficial effects on human health. The aim of this study was to evaluate the potential benefits of CLA pretreatment in a rat model of renal ischemia/reperfusion injury (IRI).

METHODS AND RESULTS

Animals were treated with CLAs (200 mg/kg/day) or water for two weeks prior to sham surgery or to surgery to induce IRI. Renal function, oxidative stress, apoptosis, and cell proliferation markers, were evaluated. Moreover, kidney sections were submitted to histological evaluation. IRI induced increased serum creatinine, blood urea nitrogen, fractional sodium excretion, malondialdehyde, Bax, and phosphorylated mammalian target of rapamycin (P-mTOR), and decreased clearance of creatine, superoxide dismutase and catalase activities, and Bax in comparison with control groups. CLA prefeeding restored, at least in part, the above reported markers to normal levels, increased the anti-apoptotic protein, B-cell lymphoma 2 (Bcl-2), and reduce the histological damage.

CONCLUSION

The results suggest that the decreased renal tissue damage and improved renal function and oxidative stress, in rats pretreated with CLAs before renal IRI induction, could be associated with downregulation of Bax and P-mTOR, and upregulation of Bcl-2. CLAs pretreatment resulted to protect against IRI through the regulation of signaling pathways involved in apoptosis.

Rodent models of heart failure: an updated review

Heart failure (HF) is one of the major health and economic burdens worldwide, and its prevalence is continuously increasing. The study of HF requires reliable animal models to study the chronic changes and pharmacologic interventions in myocardial structure and function and to follow its progression toward HF. Indeed, during the past 40 years, basic and translational scientists have used small animal models to understand the pathophysiology of HF and find more efficient ways of preventing and managing patients suffering from congestive HF (CHF). Each species and each animal model has advantages and disadvantages, and the choice of one model over another should take them into account for a good experimental design. The aim of this review is to describe and highlight the advantages and drawbacks of some commonly used HF rodents models, including both non-genetically and genetically engineered models, with a specific subchapter concerning diastolic HF models.

Cardiac sympathetic hyperinnervation in deoxycorticosterone acetate-salt hypertensive rats

Sympathetic activities are elevated in the central SNSs (sympathetic nervous systems) of hypertensive animals, but it is not known whether sympathetic innervation is also elevated in the heart. Sympathetic hyper-responsiveness in hypertension may result from oxidative stress. The aim of the present study was to investigate sympathetic hyperinnervation in DOCA (deoxycorticosterone acetate)-salt hypertensive rats with established hypertension. At 4 weeks after the start of DOCA-salt treatment and uninephrectomization, male Wistar rats were randomized into three groups for 8 weeks: vehicle, NAC (N-acetylcysteine) and triple therapy (hydralazine, hydrochlorothiazide and reserpine). DOCA-salt was associated with increased oxidant release. DOCA-salt produced concentric left ventricular hypertrophy and cardiomyocyte hypertrophy. Sympathetic hyperinnervation was observed in DOCA-salt rats, as assessed by myocardial noradrenaline levels, immunofluorescent analysis of tyrosine hydroxylase, growth-associated factor 43 and neurofilament and Western blotting and real-time quantitative RT-PCR (reverse transcription-PCR) of NGF (nerve growth factor). Arrhythmic scores during programmed stimulation in DOCA-salt rats were significantly higher than those in the control rats. Triple therapy, despite being effective on BP (blood pressure), offered neither attenuated cardiomyocyte hypertrophy nor anti-arrhythmia. The effects of DOCA-salt treatment on NGF expression, sympathetic hyperinnervation and arrhythmias were attenuated by NAC. Furthermore, the effects of NAC on NGF were abolished by administering BSO (L-buthionine sulfoximine), an inhibitor of glutamate-cysteine ligase. In conclusion, DOCA-salt treatment contributes to up-regulation of NGF proteins probably through a free radical-dependent pathway in a BP-independent manner. DOCA-salt rats treated with NAC attenuate sympathetic hyperinnervation and thus show a beneficial effect on arrhythmogenic response to programmed electrical stimulation.

Pathophysiological roles of endothelin receptors in cardiovascular diseases

Endothelin (ET)-1 derived from endothelial cells has a much more important role in cardiovascular system regulation than the ET-2 and ET-3 isoforms. Numerous lines of evidence indicate that ET-1 possesses a number of biological activities leading to cardiovascular diseases (CVD) including hypertension and atherosclerosis. Physiological and pathophysiological responses to ET-1 in various tissues are mediated by interactions with ET(A)- and ET(B)-receptor subtypes. Both subtypes on vascular smooth muscle cells mediate vasoconstriction, whereas the ET(B)-receptor subtype on endothelial cells contributes to vasodilatation and ET-1 clearance. Although selective ET(A)- or nonselective ET(A)/ET(B)-receptor antagonisms have been assumed as potential strategies for the treatment of several CVD based on clinical and animal experiments, it remains unclear which antagonisms are suitable for individuals with CVD because upregulation of the nitric oxide system via the ET(B) receptor is responsible for vasoprotective effects such as vasodilatation and anti-cell proliferation. In this review, we have summarized the current understanding regarding the role of ET receptors, especially the ET(B) receptor, in CVD.

Modulators of the vascular endothelin receptor in blood pressure regulation and hypertension

Endothelin (ET) is one of the most investigated molecules in vascular biology. Since its discovery two decades ago, several ET isoforms, receptors, signaling pathways, agonists and antagonists have been identified. ET functions as a potent endothelium-derived vasoconstrictor, but could also play a role in vascular relaxation. In endothelial cells, preproET and big ET are cleaved by ET converting enzymes into ET-1, -2, -3 and -4. These ET isoforms bind with different affinities to ET(A) and ET(B) receptors in vascular smooth muscle (VSM), and in turn increase [Ca(2+)](i), protein kinase C and mitogen-activated protein kinase and other signaling pathways of VSM contraction and cell proliferation. ET also binds to endothelial ET(B) receptors and stimulates the release of nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. ET, via endothelial ET(B) receptor, could also promote ET re-uptake and clearance. While the effects of ET on vascular reactivity and growth have been thoroughly examined, its role in the regulation of blood pressure and the pathogenesis of hypertension is not clearly established. Elevated plasma and vascular tissue levels of ET have been identified in salt-sensitive hypertension and in moderate to severe hypertension, and ET receptor antagonists have been shown to reduce blood pressure to variable extents in these forms of hypertension. The development of new pharmacological and genetic tools could lead to more effective and specific modulators of the vascular ET system for treatment of hypertension and related cardiovascular disease.

Reduced NO production rapidly aggravates renal function through the NF-κB/ET-1/ETA receptor pathway in DOCA-salt-induced hypertensive rats

AIMS

It has been reported that endothelin-1 (ET-1) overproduction and reduced nitric oxide (NO) production are closely related to the progression of renal diseases. In the present study, we examined the interrelation between ET-1 and NO system using rats treated with the combination of deoxycorticosterone acetate (DOCA)-salt and a non selective NO synthase inhibitor N(ω)-nitro-L-arginine (NOARG).

MAIN METHODS

Rats were treated with DOCA-salt (15 mg/kg, plus drinking water containing 1% NaCl) for two weeks, and then additional treatment of NOARG (0.6 mg/ml in the drinking water) was performed for three days.

KEY FINDINGS

Combined treatment of DOCA-salt and NOARG drastically developed the severe renal dysfunction and tissue injury. This treatment additionally enhanced renal ET-1 production compared to the rats treated with DOCA-salt alone, whereas a selective ET(A) receptor antagonist ABT-627 completely prevented renal dysfunction and tissue injury. On the other hand, combined treatment of DOCA-salt and NOARG induced the phosphorylation of inhibitory protein kappa B (IκB), followed by the activation of nuclear factor-kappa B (NF-κB) in the kidney. In addition, pyrrolidine-dithiocarbamate completely suppressed not only NF-κB activation but also renal dysfunction and ET-1 overproduction.

SIGNIFICANCE

These results suggest that NF-κB/ET-1/ET(A) receptor-mediated actions are responsible for the increased susceptibility to DOCA-salt induced renal injuries in the case of reduced NO production.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.

Endothelin 1 activation of endothelin A receptor/NADPH oxidase pathway and diminished antioxidants critically contribute to endothelial progenitor cell reduction and dysfunction in salt-sensitive hypertension

Circulating endothelial progenitor cells (EPCs) are reduced in hypertension, which inversely correlates with its mortality. Deoxycorticosterone acetate (DOCA)-salt hypertension features elevated endothelin (ET) 1 and oxidative stress. We tested the hypothesis that ET-1 induces EPC dysfunction by elevating oxidative stress through the ET(A)/NADPH oxidase pathway in salt-sensitive hypertension. Both ET(A) and ET(B) receptors were expressed in EPCs, but only ET(A) receptors were significantly increased in EPCs of DOCA-salt rats. EPC number and function were reduced in DOCA-salt rats compared with sham controls, and both were reversed by in vivo blockade of ET(A) receptors or NADPH oxidase. The enzymatic activities of NAPDH oxidase and its subunits gp91(phox), p22(phox), and Rac1 were augmented in EPCs of DOCA-salt rats, with concomitantly decreased antioxidant enzymes manganese superoxide dismutase, copper-zinc superoxide dismutase, and glutathione peroxidase 1. Reactive oxygen species level was elevated in EPCs from DOCA-salt rats, accompanied by increased EPC telomerase inactivation, senescence, and apoptosis, which were rescued by ET(A) or NADPH oxidase blockade. Cell therapy of normal or treated DOCA EPCs, but not untreated DOCA EPCs, significantly increased capillary density and blood perfusion in ischemic hindlimbs of DOCA-salt rats. p53 and Bax/Bcl-2 ratios were increased in EPCs of DOCA-salt rats, which were reversed by ET(A) antagonist, NADPH oxidase inhibitor, or polyethylene glycol-superoxide dismutase. Finally, in ET(B)-deficient rats, plasma ET-1 was elevated, and EPC number and telomerase activity were diminished. These results demonstrate, for the first time, that both ET-1 activation of ET(A)/NADPH oxidase pathway and diminished antioxidants critically contribute to EPC reduction and dysfunction via increased oxidative stress in salt-sensitive hypertension.

Regulation of sodium transport in the proximal tubule by endothelin

Human essential hypertension and rodent genetic hypertension are associated with increased sodium transport in the renal proximal tubule and medullary thick ascending limb of Henle. The proximal tubule, which secretes endothelin (ET), expresses the ET(B) receptor. Low (nM) concentrations of ET, via the ET(B) receptor, inhibit sodium and water transport and ATP-driven drug secretion in the proximal tubule. In contrast, very low (pM) and high nM concentrations of ET increase renal proximal sodium transport, but the receptor involved remains to be determined. The natriuretic effect of ET(B) receptor stimulation is impaired in spontaneously hypertensive rats, due in part to a defective interaction with D(3) dopamine and angiotensin II type 1 receptors. Impaired ET(B) receptor function in the renal proximal tubule may be important in the pathogenesis of genetic hypertension.

Effect of pravastatin on nephroprotection in deoxycorticosterone acetate-salt hypertensive rats

OBJECTIVE

Endothelin-1 (ET-1) has been implicated in the pathogenesis of renal impairment. The current study was undertaken to assess the effect of pravastatin on the progression of renal impairment in deoxycorticosterone acetate (DOCA)-salt hypertensive rats.

METHODS

Four weeks after the start of DOCA-salt treatment and uninephrectomization, male Wistar rats were treated with one of the following therapies for 8 weeks: vehicle; a nonselective endothelin receptor antagonist bosentan; pravastatin; or hydralazine.

RESULTS

Treatment with bosentan or pravastatin was associated with reductions in blood pressure and renal medullary hydroxyproline content, and improvement in glomerular filtration rate, urinary protein excretion, macrophage infiltration, tubular injury, and vascular injury, but not glomerulosclerosis. The renal medullary ET-1 protein levels and preproET-1 mRNA assessed by western blotting and real-time quantitative reverse transcription-PCR were significantly decreased (both P < 0.001) in the pravastatin-treated rats compared with vehicle, which was also confirmed by immunohistochemical analysis. However, there were no significant differences of ET-1 levels in the renal cortex among the DOCA-salt groups. The nephroprotective effects of pravastatin were not associated with its antihypertensive action because hydralazine despite reducing blood pressure failed to improve renal function and disorder.

CONCLUSION

These results suggest a crucial role of renal endothelin system in the pathogenesis of renal functional and structural alterations in the DOCA-salt hypertensive rats. Pravastatin administration ameliorates the impairment of renal function and structures by attenuating medullary ET-1 expression, independent of systemic blood pressure.

Endothelin type A and B receptors in the control of afferent and efferent arterioles in mice

BACKGROUND

Endothelin 1 contributes to renal blood flow control and pathogenesis of kidney diseases. The differential effects, however, of endothelin 1 (ET-1) on afferent (AA) and efferent arterioles (EA) remain to be established.

METHODS

We investigated endothelin type A and B receptor (ETA-R, ETB-R) functions in the control of AA and EA. Arterioles of ETB-R deficient, rescued mice [ETB(-/-)] and wild types [ETB(+/+)] were microperfused.

RESULTS

ET-1 constricted AA stronger than EA in ETB(-/-) and ETB(+/+) mice. Results in AA: ET-1 induced similar constrictions in ETB(-/-) and ETB(+/+) mice. BQ-123 (ETA-R antagonist) inhibited this response in both groups. ALA-ET-1 and IRL1620 (ETB-R agonists) had no effect on arteriolar diameter. L-NAME did neither affect basal diameters nor ET-1 responses. Results in EA: ET-1 constricted EA stronger in ETB(+/+) compared to ETB(-/-). BQ-123 inhibited the constriction completely only in ETB(-/-). ALA-ET-1 and IRL1620 constricted only arterioles of ETB(+/+) mice. L-NAME decreased basal diameter in ETB(+/+), but not in ETB(-/-) mice and increased the ET-1 response similarly in both groups. The L-NAME actions indicate a contribution of ETB-R in basal nitric oxide (NO) release in EA and suggest dilatory action of ETA-R in EA.

CONCLUSIONS

ETA-R mediates vasoconstriction in AA and contributes to vasoconstriction in EA in this mouse model. ETB-R has no effect in AA but mediates basal NO release and constriction in EA. The stronger effect of ET-1 on AA supports observations of decreased glomerular filtration rate to ET-1 and indicates a potential contribution of ET-1 to the pathogenesis of kidney diseases.

Rosiglitazone prevents the progression of renal injury in DOCA-salt hypertensive rats

This study was designed to evaluate the possible renoprotective effects of rosiglitazone (RGT), a peroxisome proliferator-activated subtype gamma receptor agonist, in deoxycorticosterone acetate (DOCA)-salt hypertension and its role in endogenous endothelin-1 (ET-1) production and renal fibrosis associated with inflammation. Rats were implanted with DOCA strips (200 mg kg(-1)) at 1 week after unilateral nephrectomy. DOCA-salt rats received control diet with or without RGT (10 mg kg(-1) per day). Systolic blood pressure was measured by the tail-cuff method. Glomerulosclerosis and tubulointerstitial fibrosis were evaluated on kidney sections. The expression of ED-1, cyclooxygenase-2 (COX-2), heat shock protein-25 (HSP25) and transforming growth factor-beta1 (TGF-beta1) was determined in the kidney by semiquantitative immunoblotting. In DOCA-salt rats, systolic blood pressure was increased, whereas creatinine clearance decreased compared with controls, which were counteracted by RGT treatment. Tubular injury and glomerulosclerois in the histological study were prominent in DOCA-salt rats, which were counteracted by RGT treatment. ET-1 expression was increased in DOCA-salts rats, which was attenuated by RGT treatment. The expression of TGF-beta1, ED-1 and COX-2 was increased in DOCA-salt, which was attenuated by RGT treatment. In conclusion, RGT treatment decreases blood pressure and is effective in preventing the progression of renal injury in DOCA-salt hypertension, the mechanisms of which are associated with anti-inflammatory and anti-fibrotic effects through reducing the overexpression of ET-1, ED-1, COX-2 and TGF-beta1 in the kidney.

Cardiovascular responses to cold exposure

The prevalence of hypertension is increased in winter and in cold regions of the world. Cold temperatures make hypertension worse and trigger cardiovascular complications (stroke, myocardial infarction, heart failure, etc.). Chronic or intermittent exposure to cold causes hypertension and cardiac hypertrophy in animals. The purpose of this review is to provide the recent advances in the mechanistic investigation of cold-induced hypertension (CIH). Cold temperatures increase the activities of the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). The SNS initiates CIH via the RAS. Cold exposure suppresses the expression of eNOS and formation of NO, increases the production of endothelin-1 (ET-1), up-regulates ETA receptors, but down-regulates ETB receptors. The roles of these factors and their relations in CIH will be reviewed.

Experimental animal models of hypertension

Hypertension (HTN) and cardiovascular disease are the most common causes of death in developed countries. The use of experimental animal models of HTN has provided valuable information regarding many aspects of HTN, including etiology, pathophysiology, complications, and treatment. Because the etiology of HTN is heterogeneous, many experimental animal models have been developed to mimic the many facets of human HTN. The choice of animal model will be determined by the research question, monetary limitations, and technical expertise. The categories of models of HTN are: renovascular, renal parenchymal, pharmacologically induced, environmentally induced, and genetic. There are considerable differences between HTN in animals and humans, including differences in homeostatic mechanisms and pathophysiology; therefore, a thorough understanding of the animal models and rigorous analysis is required before extrapolating the finding in animals to humans.

Drug discovery for overcoming chronic kidney disease (CKD): the endothelin ET B receptor/nitric oxide system functions as a protective factor in CKD

Accelerated cardiovascular disease (CVD) is a frequent complication of renal disease. Chronic kidney disease (CKD) develops hypertension and dyslipidemia, which in turn can contribute to the progression of renal failure. There is general agreement that endothelin-1 (ET-1), which acts through the two subtypes of receptor ET(A) and ET(B), plays important physiological roles in the regulation of normal cardiovascular function and that excessive ET-1 production is linked to CVD and CKD. Although selective ET(A) or nonselective ET(A)/ET(B) receptor antagonisms have been recognized as a potential strategy for treatment of several cardiovascular disease, it remains unclear which of the antagonisms is suitable for the individuals with CKD because upregulation of the nitric oxide (NO) system via ET(B) receptor is responsible for renal function such as natriuresis, diuresis, and glomerular hemodynamics. Our findings clearly indicate that the blockade of ET receptors, in particular ET(A)-receptor antagonism, not only produces a potential renoprotective effect in CKD but also reduces the risk of CVD. In contrast, pharmacological blockade or genetic deficiency of ET(B) receptor seems to aggravate CKD and CVD in several experimental models of rats. Moreover, preliminary evidence in patients with CKD also suggests that both selective ET(A)- and nonselective ET(A)/ET(B)-receptor blockade decreases blood pressure but that selective ET(A) blockade has additional desirable effects on renal hemodynamics. Thus, at least in CKD, these findings support the notion that ET(B) receptor-mediated actions produce a renoprotective effect and that nonselective ET(A)/ET(B)-receptors blockade seem to offer no advantage over selective ET(A) antagonism, and if anything may potentially reduce the benefits.

Polymorphisms of the endothelin-1 gene associate with hypertension in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) associates with excess cardiovascular (CV) morbidity and mortality. Hypertension, a highly prevalent entity in RA, has been associated with the endothelin-1 (ET-1) gene locus (EDN1) in some groups, such as Afro-Caribbean, the obese, and in low-renin states, but not in the general population as a whole. High levels of plasma ET-1 have been observed in RA. This study evaluated the potential association of EDN1 gene locus and serum ET-1 levels with hypertension in patients with RA. Genomic DNA and serum samples were collected from 397 well-characterized RA patients; DNA was also available from 401 local general population controls without RA. To explore the overall relevance of EDN1, two suitable single-nucleotide polymorphisms (SNPs), rs1800541 and rs5370, were selected and haplotype analysis was performed. Both SNPs were identified using real-time polymerase chain reaction (PCR) and melting curve analysis. Genetic analysis was related to hypertension as dichotomous trait and to blood pressure indices as continuous variables. Serum endothelin levels were also assessed in the RA patients. No genotype or haplotype differences were observed between RA and control subjects. Within RA, logistic regression analysis of each SNP separately revealed a threefold increase in the adjusted odds of being hypertensive of rs5370 TT homozygotes compared to GG homozygotes (OR = 2.89, 95%CI: 1.02 to 8.19). After adjustment for multiple potential confounders, haplotype analysis revealed an additive effect of the rs1800541-rs5370 T-T haplotype on hypertension (OR = 2.96, 95%CI: 1.28 to 6.86; p = .011), systolic blood pressure (SBP) (beta = 6.75 +/- 2.57 mm Hg; p = .009), and pulse pressure (PP) (beta = 4.37 +/- 2.12 mm Hg; p = .040). There was an increased prevalence of raised ET-1 levels amongst hypertensive RA patients, whereas a similar trend was observed for T-T haplotype carriers. RA patients who carry the rs1800541-rs5370 T-T EDN1 haplotype appear more likely to be hypertensive with an increased SBP and PP. These findings, if replicated in future studies, could be used as a screening tool for RA patients at increased hypertension, and thus cardiovascular, risk.

TNF-alpha inhibition reduces renal injury in DOCA-salt hypertensive rats

Studies suggest that the inflammatory cytokine TNF-alpha plays a role in the prognosis of end-stage renal diseases. We previously showed that TNF-alpha inhibition slowed the progression of hypertension and renal damage in angiotensin II salt-sensitive hypertension. Thus, we hypothesize that TNF-alpha contributes to renal inflammation in a model of mineralocorticoid-induced hypertension. Four groups of rats (n = 5 or 6) were studied for 3 wk with the following treatments: 1) placebo, 2) placebo + TNF-alpha inhibitor etanercept (1.25 mg.kg(-1).day(-1) sc), 3) deoxycorticosterone acetate + 0.9% NaCl to drink (DOCA-salt), or 4) DOCA-salt + etanercept. Mean arterial blood pressure (MAP) measured by telemetry increased in DOCA-salt rats compared with baseline (177 +/- 4 vs. 107 +/- 3 mmHg; P < 0.05), and TNF-alpha inhibition had no effect in the elevation of MAP in these rats (177 +/- 8 mmHg). Urinary protein excretion significantly increased in DOCA-salt rats compared with placebo (703 +/- 76 vs. 198 +/- 5 mg/day); etanercept lowered the proteinuria (514 +/- 64 mg/day; P < 0.05 vs. DOCA-salt alone). Urinary albumin excretion followed a similar pattern in each group. Urinary monocyte chemoattractant protein (MCP)-1 and endothelin (ET)-1 excretion were also increased in DOCA-salt rats compared with placebo (MCP-1: 939 +/- 104 vs. 43 +/- 7 ng/day, ET-1: 3.30 +/- 0.29 vs. 1.07 +/- 0.03 fmol/day; both P < 0.05); TNF-alpha inhibition significantly decreased both MCP-1 and ET-1 excretion (409 +/- 138 ng/day and 2.42 +/- 0.22 fmol/day, respectively; both P < 0.05 vs. DOCA-salt alone). Renal cortical NF-kappaB activity also increased in DOCA-salt hypertensive rats, and etanercept treatment significantly reduced this effect. These data support the hypothesis that TNF-alpha contributes to the increase in renal inflammation in DOCA-salt rats.

[Endothelin-1 production and its involvement in cardiovascular diseases]

Endothelin (ET) has been implicated in the pathogenesis of several cardiovascular disorders because of its powerful vasoconstrictor and growth-promoting properties. The ET family consists of three isoforms, ET-1, ET-2 and ET-3. ET-1 appears to be the predominant member of the family generated by vascular endothelial cells. In view of the multiple cardiovascular actions of ET-1, there has been much interest in its contribution to the pathophysiology of hypertension and arteriosclerosis. We have been investigating the roles of ET(A) and ET(B) receptors in ET-1-related cardiovascular diseases using subtype-selective ET receptor antagonists and ET(B) receptor-deficient animals. Our studies have demonstrated that ET-1 overproduction and ET(A)-mediated ET-1 actions seem to play a crucial role in the development of several types of hypertensive and post-ischemic diseases. On the other hand, ET-1 biosynthesis and release are regulated at the transcriptional level, and various endogenous substances are known to stimulate ET-1 gene expression by DNA binding of transcription factors. We and others have recently demonstrated that nuclear factor-kappaB (NF-kappaB), a transcription factor with a pivotal role in inducing genes involved in immune, inflammatory and stress responses, is responsible for endothelial ET-1 production. In in vivo studies, agents that can inhibit the NF-kappaB activation improved the development of ET-1-related cardiovascular diseases. Thus, NF-kappaB inhibition may be a pertinent treatment for ET-1 related diseases.

Pathophysiological Mechanisms of Salt-Dependent Hypertension

Changes in salt intake are associated in general with corresponding changes in arterial blood pressure. An exaggerated increment in blood pressure driven by a salt load is characteristic of salt-sensitive hypertension, a condition affecting more than two thirds of individuals with essential hypertension who are older than 60 years. In the last decade, significant insight was gained about the role of the kidney in the increment in blood pressure induced by sodium retention. The present review focuses on the pathophysiological characteristics of the blood pressure increase driven by expansion of extracellular fluid and the increment in plasma sodium concentration. In addition, we discuss systemic and renal conditions that result in decreased urinary sodium excretion and were implicated in the development of salt-sensitive hypertension.

Involvement of the endothelin ET(B) receptor in gender differences in deoxycorticosterone acetate-salt-induced hypertension

1. In the present study, we investigated the role of endothelin ET(B) receptors in gender differences in the development of deoxycorticosterone acetate (DOCA)-salt-induced hypertension by using the spotting-lethal (sl) rat, which carries a naturally occurring deletion in the ET(B) receptor gene. 2. In wild-type rats, the elevation of systolic blood pressure (SBP) by DOCA-salt treatment for 4 weeks was extremely lower in females than in males, but this gender difference was partially attenuated in ovariectomized (OVX) animals. These alterations of SBP corresponded with vascular superoxide () production. 3. In homozygous (sl/sl) group, the SBP of male, intact female and OVX rats was markedly elevated by DOCA-salt treatment to the same extent, indicating that the gender difference in DOCA-salt-induced hypertension was abolished by the genetic ET(B) receptor deficiency. There were similar increases in the vascular endothelin (ET)-1 content in the three DOCA-salt-treated animal groups, but vascular production in male and OVX rats was much higher than that in intact females. 4. Daily oral administration of ABT-627, an ET(A) receptor antagonist, to sl/sl rats for 2 weeks suppressed the DOCA-salt-induced hypertension more efficiently in intact female rats than in male animals. 5. Thus, vascular oxidative stress is related, at least in part, to differences in the development of DOCA-salt-induced hypertension between male and female rats, but this gender difference is abolished by the genetic ET(B) receptor deficiency, suggesting that ET(B) receptor-mediated vasoprotective actions contribute to the gender differences seen. In addition, in both sexes, vascular ET-1 overproduction and the ET(A) receptor-mediated action seem to be responsible for the enhanced susceptibility to DOCA-salt hypertension in genetic ET(B) receptor deficiency.

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Increased sympathetic venoconstriction and reactivity to norepinephrine in mesenteric veins in anesthetized DOCA-salt hypertensive rats

Increased sympathetic nervous activity (SNA) elevates venomotor tone in deoxycorticosterone acetate (DOCA)-salt hypertension. We studied the mechanisms by which the SNA increases venomotor tone in DOCA-salt hypertension by making in situ intracellular recordings of venous smooth muscle cell (VSMC) membrane potential (E(m)) and measurement of outside diameter (OD) in mesenteric veins (MV) and mesenteric arteries (MA) of anesthetized rats. We also studied norepinephrine (NE)- and endothelin-1 (ET-1)-induced increases in MA or MV perfusion pressure (PP) in vitro. E(m) in DOCA-salt MV was depolarized compared with sham MV. Prazosin hyperpolarized VSMC E(m) in DOCA-salt but not in sham MV. NE concentration-response curves (CRCs) for OD decreases in MV from DOCA-salt rats were left-shifted with an increased maximum response (E(max)) compared with sham MV. NE CRCs for OD decreases in MA were right-shifted with reduced E(max) in DOCA-salt compared with sham rats. ET-1 CRCs were similar in DOCA-salt and sham MV but were right-shifted with reduced E(max) in DOCA-salt MA. NE CRCs for MAPP increases were left-shifted without a change in E(max) in DOCA-salt rats. NE did not change MVPP. MAPP and MVPP for ET-1 CRCs were similar in sham and DOCA-salt rats, but E(max) for MAPP was reduced in DOCA-salt rats. Hematoxylin staining revealed hypertrophy in DOCA-salt MA but not in MV. We conclude that there is increased reactivity to NE released from the sympathetic nervous system in DOCA-salt MV that causes VSMC depolarization and increased venomotor tone. In DOCA-salt rats, in vivo ET-1 reactivity is maintained in MV, but reduced in MA.

Mechanisms of Hypertension Induced by Nitric Oxide (NO) Deficiency: Focus on Venous Function

Loss of endothelial cell-derived nitric oxide (NO) in hypertension is a hallmark of arterial dysfunction. Experimental hypertension created by the removal of NO, however, involves mechanisms in addition to decreased arterial vasodilator activity. These include augmented endothelin-1 (ET-1) release, increased sympathetic nervous system activity, and elevated tissue oxidative stress. We hypothesized that increased venous smooth muscle (venomotor) tone plays a role in Nomega-nitro-L-arginine (LNNA) hypertension through these mechanisms. Rats were treated with the NO synthase inhibitor LNNA (0.5 g/L in drinking water) for 2 weeks. Mean arterial pressure of conscious rats was 119 +/- 2 mm Hg in control and 194 +/- 5 mm Hg in LNNA rats (P<0.05). Carotid arteries and vena cava were removed for measurement of isometric contraction. Maximal contraction to norepinephrine was modestly reduced in arteries from LNNA compared with control rats whereas the maximum contraction to ET-1 was significantly reduced (54% control). Maximum contraction of vena cava to norepinephrine (37% control) also was reduced but no change in response to ET-1 was observed. Mean circulatory filling pressure, an in vivo measure of venomotor tone, was not elevated in LNNA hypertension at 1 or 2 weeks after LNNA. The superoxide scavenger tempol (30, 100, and 300 micromol kg(-1), IV) did not change arterial pressure in control rats but caused a dose-dependent decrease in LNNA rats (-18 +/- 8, -26 +/- 15, and -54 +/- 11 mm Hg). Similarly, ganglionic blockade with hexamethonium caused a significantly greater fall in LNNA hypertensive rats (76 +/- 9 mm Hg) compared with control rats (35 +/- 10 mm Hg). Carotid arteries, vena cava, and sympathetic ganglia from LNNA rats had higher basal levels of superoxide compared with those from control rats. These data suggest that while NO deficiency increases oxidative stress and sympathetic activity in both arterial and venous vessels, the impact on veins does not make a major contribution to this form of hypertension.

Effects of chronic cold exposure on the endothelin system

Cold temperatures have adverse effects on the human cardiovascular system. Endothelin (ET)-1 is a potent vasoconstrictor. We hypothesized that cold exposure increases ET-1 production and upregulates ET type A (ETA) receptors. The aim of this study was to determine the effect of cold exposure on regulation of the ET system. Four groups of rats (6–7 rats/group) were used: three groups were exposed to moderate cold (6.7 ± 2°C) for 1, 3, and 5 wk, respectively, and the remaining group was maintained at room temperature (25°C) and served as control. Cold exposure significantly increased ET-1 levels in the heart, mesenteric arteries, renal cortex, and renal medulla. Cold exposure increased ETA receptor protein expression in the heart and renal cortex. ET type B (ETB) receptor expression, however, was decreased significantly in the heart and renal medulla of cold-exposed rats. Cold exposure significantly increased the ratio of ETA to ETB receptors in the heart. An additional four groups of rats (3 rats/group) were used to localize changes in ETA and ETB receptors at 1, 3, and 5 wk of cold exposure. Immunohistochemical analysis showed an increase in ETA, but a decrease in ETB, receptor immunoreactivity in cardiomyocytes of cold-exposed rats. Increased ETA receptor immunoreactivity was also found in vascular smooth muscle cells of cold-exposed rats. Cold exposure increased ETA receptor immunoreactivity in tubule epithelial cells in the renal cortex but decreased ETB receptor immunoreactivity in tubule epithelial cells in the renal medulla. Therefore, cold exposure increased ET-1 production, upregulated ETA receptors, and downregulated ETB receptors.

The future of endothelin-receptor antagonism as treatment for systemic hypertension

Endothelin (ET) is an endogenous peptide secreted predominantly by endothelial cells that mediates its effects via vasoconstriction and hypertrophy of vascular smooth muscle. Because the role of ET has been described in multiple pathologic processes in cardiovascular disease, including hypertension, there has been a strong interest in the development of therapeutic agents that inhibit ET receptors. ET receptor antagonists have shown much promise in disease states such as pulmonary arterial hypertension, essential hypertension, and various forms of secondary hypertension. This review serves to summarize the current role of ET and ET receptor antagonists in both the pathophysiology and the treatment of hypertension.

The vascular endothelin system in hypertension--recent patents and discoveries

The discovery of endothelin two decades ago has now evolved into an intricate vascular endothelin (ET) system. Several ET isoforms, receptors, signaling pathways, agonists, antagonists, and clinical applications have been identified and documented in first-rate patents. The role of ET as one of the most potent endothelium-derived vasoconstricting factors is now complemented by a newly discovered role in vascular relaxation. ET synthesis is initiated by the transcription of ET genes in endothelial cells and the generation of the gene products preproET and big ET, which are further cleaved by specific ET converting enzymes into ET-1, -2, -3 and -4 isoforms. ET isoforms bind with different affinities to ET(A) and ET(B2) receptors in vascular smooth muscle, and stimulate [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other signaling mechanisms of smooth muscle contraction, growth and proliferation. ET also binds to endothelial ET(B1) receptors, which mediate the release of vasodilator substances such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. Endothelial ET(B1) receptors may also function in ET re-uptake and clearance. Although the effects of ET on vascular function and growth are well-recognized, the role of ET and its receptors in the regulation of blood pressure and in the pathogenesis of hypertension is not clearly established. Salt-dependent hypertension in experimental animals and some forms of moderate to severe hypertension in human may show elevated levels of plasma or vascular ET; however, other forms of hypertension show normal ET levels. The currently available ET receptor antagonists reduce blood pressure in some forms of experimental hypertension. Careful examination of recent patents may identify more effective and specific modulators of the vascular ET system for clinical use in human hypertension.

ETA receptor blockade prevents renal dysfunction in salt-sensitive hypertension induced by sensory denervation

To test the hypothesis that activation of the endothelin type A (ETA) receptor contributes to decreased renal excretory function and increased blood pressure in sensory nerve-degenerated rats fed a high-salt diet, neonatal Wistar rats were given vehicle or capsaicin (CAP, 50 mg/kg sc) on the first and second day of life. After being weaned, vehicle or CAP-treated rats were fed a normal (NS, 0.5%) or a high- (HS, 4%) sodium diet for 2 wk with or without ABT-627 (5 mg·kg−1·day−1, a selective ETA receptor antagonist). Systolic blood pressure increased in CAP-treated rats fed a HS diet (CAP-HS) compared with vehicle-treated rats fed a HS diet (CON-HS, 145 ± 7 vs. 89 ± 5 mmHg, P < 0.05). Creatinine clearance and fractional sodium excretion (FENa) decreased in CAP-HS rats compared with CON-HS rats (creatinine clearance, 0.54 ± 0.05 vs. 0.81 ± 0.09 ml·min−1·100 g body wt−1; FENa, 8.68 ± 0.99 vs. 12.53 ± 1.47%, respectively; P < 0.05). Water and sodium balance increased in CAP-HS rats compared with CON-HS (water balance, 20.2 ± 1.5 vs. 15.5 ± 1.9 ml/day; sodium balance, 11.9 ± 3.1 vs. 2.4 ± 0.3 meq/day, respectively; P < 0.05). The endothelin (ET)-1 levels in plasma and isolated glomeruli increased by about twofold in CAP-HS rats compared with CON-HS rats ( P < 0.05). ABT-627 prevented the decrease in creatinine clearance and FENa, the increase in water and sodium balance, and the increase in blood pressure in CAP-HS rats ( P < 0.05). Therefore, the blockade of the ETA receptor ameliorates the impairment of renal excretory function and prevents the elevation in blood pressure in salt-sensitive hypertension induced by degeneration of sensory nerves, indicating that the activation of the ETA receptor impairs renal function and contributes to the development of a salt-induced increase in blood pressure in this model.

Endothelial nitric oxide synthase is not essential for the development of fibrosis and portal hypertension in bile duct ligated mice

BACKGROUND/AIMS

It is postulated that nitric oxide (NO) is responsible for the hyperdynamic circulation of portal hypertension. Therefore, we investigated induction of fibrosis and hyperdynamic circulation in endothelial NO synthase knock-out (KO) mice.

METHODS

Fibrosis was induced by bile duct ligation. Hemodynamic studies were performed after portal vein ligation. All studies were performed in wild-type (WT) and KO mice.

RESULTS

Three to 4 weeks after bile duct ligation (BDL), both WT and KO groups had similar degrees of portal hypertension, 12 (9-14) and 11(8-15) mmHg, median (range), and liver function. Fibrosis increased from 0.0% in sham operated to 1.0 and 1.1% in WT and KO mice, respectively. Cardiac output was similar after portal vein ligation (20 and 17 ml/min in WT and KO mice, respectively). There was no difference in liver of mRNA for endothelin 1, inducible NO synthase (iNOS) and hem-oxygenase 1 (HO1); proteins of iNOS, HO1 and HO2; nor in endothelin A and B (EtA and EtB) receptor density between WT and KO mice after BDL.

CONCLUSIONS

These results suggest that endothelial NO synthase is neither essential for the development of fibrosis and portal hypertension in bile duct ligated mice, nor for the hyperdynamic circulation associated with portal hypertension in the portal vein ligated mice.

Endothelin-1 contributes to the sexual differences in renal damage in DOCA-salt rats

We investigated whether gender differences in renal damage in DOCA-salt hypertension are associated with effects of ovarian hormones and/or endothelin-1 (ET-1). Renal injuries and renal pre-pro-ET-1 mRNA expression were enhanced in male and female ovariectomized (OVX) DOCA rats versus female DOCA rats. Treatment with estrogen plus progesterone or progesterone, but not estrogen alone, attenuated renal damage and pre-pro-ET-1 mRNA expression in OVX DOCA rats. The ETA antagonist BMS182874 greatly ameliorated renal damage in male and OVX DOCA rats. In conclusion, the ovarian hormones have a protective role on the renal structural alterations in female DOCA rats by modulating effects of ET-1, via ETA receptors.

Historic perspectives and recent advances in major animal models of hypertension

Hypertension and related cardiovascular diseases are the leading causes of death in many countries. The etiology of human essential hypertension is largely unknown. It is highly likely that hypertension is a complex and multifactorial disease resulting from the interaction of multiple genetic and environmental factors. Animal models of hypertension have been proved to be useful to study the pathogenesis of, and to find a new therapy for, hypertension. The aim of this article is to briefly review the most widely used rodent models of experimental hypertension, including history and recent advances. These models are classified as genetically-induced, environmentally-induced, pharmacologically-induced, and renal-induced hypertension according to the way of induction; the typical representatives of each of these major types of experimental hypertension are spontaneous hypertension, cold-induced hypertension, DOCA-salt-induced hypertension, and renal-induced hypertension, respectively. The processes of induction of hypertension, possible pathogenesis, characteristics, advantages, and limitations of these animal models are reviewed. In addition, the clinical implications of the above experimental models of hypertension are addressed.

Antihypertensive Effect of 5-HT1A Agonist Buspirone and 5-HT2B Antagonists in Experimentally Induced Hypertension in Rats

We investigated the antihypertensive effect of 5-HT1A agonist (buspirone) and 5-HT2B antagonists (SB204741 and SB200646) in deoxycorticosterone acetate (DOCA)-salt-induced hypertensive rats. Experiments were divided into two sets: in the first set, sham-operated control and DOCA-treated hypertensive rats received buspirone (1 mg/kg/day p.o. for 4 weeks) and in the second set, in vivo and in vitro studies were carried out. In the case of in vivo studies, sham-operated control and DOCA-treated hypertensive rats received SB204741 or SB200646 (1 mg/kg/week i.v. for 4 weeks). Blood pressure was measured weekly by tail-cuff method. After completion of the treatment schedule, blood pressure and vascular reactivity to various agonists like 5-HT, noradrenaline and adrenaline were recorded. Chronic administration of buspirone, SB204741 and SB200646 produced a significant reduction in blood pressure and vascular reactivity to agonists in DOCA-salt hypertensive rats, implying an antihypertensive effect. However, chronic administration of the same drugs in sham control rats did not alter blood pressure and vascular reactivity to various agonists. For in vitro studies a similar treatment schedule was followed as in vivo studies and a cumulative concentration response curve of 5-HT was recorded on isolated thoracic aorta. Treatment with 5-HT2B antagonists shifted the concentration response curve of 5-HT to the right on isolated aorta. We conclude that 5-HT1A agonist and 5-HT2B antagonists possess an antihypertensive effect.

Roles of Endothelin ETA and ETB Receptors in the Pathogenesis of Monocrotaline-Induced Pulmonary Hypertension

The functional roles of endothelin ETA and ETB receptors in the development of monocrotaline (MCT)-induced pulmonary hypertension were investigated using MCT-treated rats in the absence or presence of a daily administration of A-192621, a selective ETB receptor antagonist, ABT-627, a selective ETA receptor antagonist, or a combination of both drugs. Four weeks after the injection of saline or MCT (60 mg/kg, s.c.), cardiac hypertrophy, right ventricular systolic pressure and morphologic changes of pulmonary arteries were evaluated. Compared with the control animals, MCT produced marked pulmonary hypertension associated with increases in right ventricular pressure and hypertrophy, and pulmonary arterial medial thickening. These MCT-induced alterations were markedly suppressed by daily treatment with ABT-627 for 4 weeks (10 mg/kg/d, twice daily), whereas treatment with A-192621 significantly aggravated the above MCT-induced pathologic changes. The blockade of both receptor subtypes by a combination of A-192621 and ABT-627 also significantly improved the MCT-induced pathologic changes, to the same extent as with ABT-627 administration. Thus, an exaggerated response to MCT during ETB receptor blockade also seems to be mediated by ETA receptor activation, thereby suggesting that ETA receptor-mediated action is exclusively contributive to the pathogenesis of MCT-induced pulmonary hypertension, although we cannot rule out a protective role of ETB receptor-mediated action.

Endothelial dysfunction in aortic rings and mesenteric beds isolated from deoxycorticosterone acetate hypertensive rats: possible involvement of protein kinase C

The main objectives of this study were to investigate the effects of deoxycorticosterone acetate (DOCA)-induced hypertension on the aortic and mesenteric vascular responses to vasodilator and vasoconstrictor agents and also to elucidate whether protein kinase C (PKC) was involved in these responses, by using chelerythrine and calphostin C, the inhibitors of protein kinase C. Hypertension was induced in male Sprague-Dawley rats (200-250 g) by DOCA-salt injection [20 mg/kg, twice weekly for 5 weeks, subcutaneously (s.c.)] and NaCl (1%) was added to their drinking water. Control rats received a saline injection (0.5 ml/kg, twice weekly for 5 weeks, s.c.), then the animals were anaesthetised [thiopental, 30 mg/kg, intraperitoneally (i.p.)] and the arterial blood pressure was measured. Mean arterial blood pressure in control and hypertensive rats were 98+/-7.5 and 163+/-3.5 mmHg, respectively (P<0.0001). In the in vitro studies, rings of descending aorta and mesenteric beds were precontracted with phenylephrine and then concentration-response curves to acetylcholine and sodium nitroprusside were constructed. In the tissue removed from hypertensive rats, the responses to acetylcholine, but not to sodium nitroprusside, were significantly reduced. However, addition of chelerythrine (10 microM) or calphostin C (100 nM) to the organ bath significantly restored these impaired responses. Our data suggest that protein kinase C plays a crucial role in the endothelial dysfunction induced by hypertension.

Effect of magnesium on mRNA expression and production of endothelin-1 in DOCA-salt hypertensive rats

The aim of this study was to investigate whether or not the decrease in blood pressure induced by dietary magnesium supplementation in DOCA-salt hypertensive rats is associated with modifications in expression and tissular production of endothelin-1. DOCA-salt treatment increased blood pressure, induced renal and cardiac hypertrophy, and increased endothelin-1 expression and production in the kidney, heart, and aorta. Mg supplementation for 8 weeks lowered blood pressure in DOCA-salt hypertensive rats and prevented hypertrophies and the increase of endothelin-1 expression and production in the heart, aorta, and kidney. Treatment with a receptor ETA antagonist, ABT-627, was used to clarify the relationship between the lowering effect of Mg supplementation on blood pressure and endothelin-1 production. When DOCA-salt rats were treated with ABT-627 for 8 weeks, Mg supplementation failed to lower blood pressure. In conclusion, these findings suggest that the lowering effect of Mg supplementation on blood pressure requires an inhibitory effect on endothelin-1 activity and/or endothelin-1 production in DOCA-salt hypertensive rats.

Role of endothelins in animal models of hypertension: focus on cardiovascular protection

Investigation of the regulation of vascular function by endothelium-derived factors has been a prominent topic of research in the field of hypertension during the last decade. Of the different endothelial factors, endothelins, which play an important role in vasodilatation-vasoconstriction balance, have been the subject of great interest and an impressive number of publications. This peptide, a very potent vasoconstrictor, triggers as well events involved in growth, proliferation, matrix production and local inflammation. In parallel, its role in hypertension has evolved from a simple vasoconstrictor to a central local regulator of vascular homeostasis contributing not only to the elevation of blood pressure, but also to the complications of hypertension. This review summarizes research on endothelins and its receptor antagonists in experimental hypertension, with special emphasis on vascular remodeling and target-organ protection.

Nephroprotective effects of the endothelin ET(A) receptor antagonist darusentan in salt-sensitive genetic hypertension

We tested the effect of selective endothelin ET(A) receptor blockade on the development renal damage in the Sabra rat model of genetic salt-sensitivity. Animals from the salt-sensitive (SBH/y) and salt-resistant strains (SBN/y) were either salt-loaded with deoxycorticosterone acetate and salt (DOCA) or fed a normal diet. Additional salt-loaded groups were also treated with the selective ET(A) antagonist darusentan (DA). Salt-loading in SBH/y increased systolic blood pressure by 75 mm Hg and urinary albumin excretion 23-fold (P<0.0001). Darusentan attenuated the rise of systolic blood pressure (50%) and urinary albumin excretion (63%, P<0.01, respectively). Salt-loading in SBH/y was associated with significant increased osteopontin mRNA expression as well as glomerulosclerosis and tubulointerstitial damage in the kidney (P<0.05, respectively). This was either significantly reduced or normalized by darusentan (P<0.05, respectively). Thus, darusentan confers a significant renal protection in the Sabra model of salt-sensitive hypertension.

Endothelin a receptor blockade and endothelin B receptor blockade improve hypokalemic nephropathy by different mechanisms

Hypokalemia causes renal tubulointerstitial injury with an elevation in renal endothelin-1 (ET-1). It was hypothesized that hypokalemic tubulointerstitial injury is ameliorated by the blockade of ET-A receptors (ETA), whereas ET-B receptor (ETB) antagonism may exacerbate the injury, because ETB is thought to mediate vasodilation. Rats were fed a K(+)-deficient diet alone (LC) or with an ETA-selective antagonist ABT-627 (LA) or an ETB-selective antagonist A-192621 (LB) for 8 wk. Control rats were on a normal K(+) diet alone or with the ETA-selective or ETB-selective antagonists. The severity of hypokalemia was not significantly different among LA, LB, and LC. LC developed tubulointerstitial injury with an elevation of renal preproET-1 mRNA level. There was an increase in tubular osteopontin expression, macrophage infiltration, collagen accumulation, and tubular cell hyperplasia. ETA blockade significantly ameliorated all parameters for renal injury in the cortex without suppressing local ET-1 and ETA expression. By contrast, ETB blockade significantly reduced local ET-1 and ETA expression and improved the injury to a similar extent in the cortex. In the medulla, ETA or ETB blockade only partially blocked renal injury. ETA blockade did not affect BP in normokalemic or hypokalemic rats. ETB blockade induced a BP elevation with a decrease in urinary Na(+) excretion in normokalemic but not in hypokalemic rats. These results indicate that ET-1 can mediate hypokalemic renal injury in two different ways: by directly stimulating ETA and by locally promoting endogenous ET-1 production via ETB. Thus, ETA as well as ETB blockade may be renoprotective in hypokalemic nephropathy.

New therapeutics that antagonize endothelin: promises and frustrations

The discovery of endothelin--a highly potent endogenous vasoconstrictor - in 1988 has led to considerable efforts to develop antagonists of endothelin receptors that could have therapeutic potential in disorders including hypertension, heart failure and renal diseases. However, in general, the results of trials in humans have not mirrored the highly promising effects in animal disease models. Here, we discuss preclinical and clinical results with endothelin antagonists, and consider possible approaches to fully realizing the potential of endothelin antagonism.

Role of endothelin B receptor in the pathogenesis of ischemic acute renal failure

This study evaluated the role of endothelin B (ET ) receptor-mediated action in the development and maintenance of ischemic acute renal failure (ARF), using the spotting-lethal ( ) rat that carries a naturally occurring deletion in the ET receptor gene. Because homozygous ( ) rats die shortly after birth due to congenital distal intestinal aganglionosis, genetic rescue of rats from the developmental defect using a dopamine-beta-hydroxylase (DbetaH)-ET transgene was performed to produce ET -deficient adult rats. Rescued homozygous (DbetaH-ET ) and wild-type (DbetaH-ET +/+) rats were subjected to ischemic ARF by clamping the renal pedicle for 45 min followed by reperfusion. At 24 h after the reperfusion, renal glomerular dysfunction and histologic damage, such as proteinaceous casts in tubuli, were markedly and observed equally in homozygous and wild-type groups, and these renal injuries gradually recovered. However, when the ischemia/reperfusion-induced renal injury was examined 7 days after the reperfusion, the recovery in homozygous ARF rats was obviously delayed compared with the wild-type animals. Two of the eight homozygous ARF rats died within 3 days after the reperfusion. Increment of renal endothelin-1 content after the ischemia/reperfusion was more marked in homozygous than in wild-type rats. Thus, ET receptor-mediated actions do not play an important role in the development of ischemic ARF but may be involved in the recovery process from ischemia/reperfusion-induced renal injury.