Hypertension In Experimental Animals Research Articles

CL-1: WISDOM FOR CONQUERING HYPERTENSION---FOOD, MOVE, AI: TOWARDS SUSTAINABLE WELL-BEING

To obtain the wisdom for conquering hypertension, in ISH2022KYOTO, we propose three new hypertension research fields, that is, FOOD (nutrition), MOVE (physical fitness) and AI (digital transformation). In 2003, I propose the clinical concept of “Metabolic Domino”, which illustrates the whole picture of non-communicable diseases (NCDs), including hypertension, beginning from derangement of lifestyle (FOOD and MOVE) and deposition of visceral fat. 1) FOOD: In 2022, we elucidate the important role of the kidney and intestines which (re)absorb sugar and salt “greedily” by the activation of “greedy genes,” the genes to be activated by excessive sugar and salt, including SGLT (sodium-glucose co-transporter)1,2 and MR (mirenalocorticoid receptor) genes, and cause hypertension/CKD and obesity/diabetes mellitus (“Greedy Organ Hypothesis”). Overactivation of MR by salt or sugar induces “MR-associated hypertension” with wide range of plasma aldosterone level. 2) MOOVE: By exercise, the increase of blood shear stress and heat rate induces the secretion of nitric oxide or natriuretic peptides, which not only reduce blood pressure but also activate mitochondria in the skeletal muscle to prevent sarcopenia and obesity. Angiotensin II has the opposite metabolic actions. 3) AI: The time-course of Metabolic Domino is now highlighted. Pre-emptive medicine or “Me-byo” (“Not-yet disease”) medicine intervenes the most upstream of Metabolic Domino to prevent occurrence of the disease. We demonstrated the transient early blockade of renin-angiotensin system can achieve prevention or regression of hypertension in experimental animals and suggested the possibility in humans. The treatment memory is mediated the alteration of epigenetic status of the organs (e.g. the kidney or blood vessels) (“Organ Memory”2018). Angiotensin II exerts modulatory effect on epigenetic change. Big data science with advanced digital technology for monitoring biorhythm data, such as blood pressure, blood glucose level, sympathetic tone or sleep depth, and also alteration of the life-environment, we will predict the specific trajectory of each individual with elevated blood pressure, and can modify organ memory and modulate the future outcome. By these innovative approaches, I will expect the establishment of the community in which no one with hypertension is left behind to serve for sustainable well-being.

The Impact of several Antihypertensive drugs and Medicinal herbs on Induced hypertension in rabbits

Objective: To assess the antihypertensive efficacy of the medicinal plants used Hibiscus subdariffa, Plantago major, Teucrium polium. Moreover, we aim to Investigate the mechanisms of actions of tested agents. Design: Induced hypertension in experimental animals is tested against several drugs and medicinal plants extracts. Animals and materials: Hypertension was induced in experimental rabbits with phenylephrine 0.2mg/kg i.v. with increasing the dose (until Blood pressure>130/90mmHg). Rabbits were divided to 7 groups: Control, atenolol, furosemide, candesartan, Hibiscus subdariffa, Plantago major, Teucrium polium. ANOVA with Dunnett's test was implemented for statistical calculations with p<0.05 as significance level. Results: Candesartan was the most effective in lowering both systolic and diastolic blood pressure. Concerning the blood flow, candesartan was found to be the most significantly effective drug in increasing blood flow followed by furosemide and Hibiscus subdariffa respectively. Concerning the urine output furosemide was found to be the most significantly effective drug in increasing urine output followed by Hibiscus subdariffa. The aqueous extracts of Plantago major and Teucrium polium showed no significant effect. Conclusions: Hibiscus subdariffa is effective as diuretic agent at the concentration mentioned. Its action involves diuretic and vasodilator effect. While aqueous extracts of Plantago major and Teucrium polium are not effective.

Gut microbiota and arterial hypertension (a literature review)

The aim of the work was to analyze and collate literature data on the role of the gut microbiota disorders in the pathogenesis of arterial hypertension and to determine the prospects for further research.Results. The article presents the results of studies that indicate the significant role of various components of the gut microbiota disorders in the development of arterial hypertension in experimental animals and humans. The accumulated data allow for consideration of the gut microiota as a part of a complex system involved in the regulation of blood pressure. Studies using fecal microbiota transplantation showed that the fecal microbiome transfer from hypertensive animals or patients with arterial hypertension to normotensive animals led to an increase in blood pressure in the latter. At the same time, transplantation of microbiota from normotensive animals to hypertensive resulted in a decrease in blood pressure in recipients. It was revealed that the leading dysbiotic factors that play the most significant role in the mechanisms of arterial hypertension development are the composition of the gut microbiota, the Firmicutes/Bacteroidetes ratio, the state of the tight junction proteins in the gut epithelium, the gut epithelial permeability to lipopolysaccharides, endotoxinemia, subclinical systemic inflammation, the levels of trimethylamine N-oxide and short-chain fatty acids production, as well as the relationship between the latter and specific Olfr and GPR receptors.Conclusions. The analyzed results of the studies indicate the involvement of gut microbiota disorders in the pathogenesis of arterial hypertension. However, the role of individual components of the gut microbiota in the mechanisms of blood pressure regulation and the development of hypertensive damage to target organs and complications remains poorly understood. Promising areas of the research are the development of informative methods for assessing the state of gut microbiota and fundamentally new approaches for reducing the risk of hypertension development and progression by the correction of occurring disorders.

Действие густого экстракта из травы первоцвета весеннего на эндотелиальную дисфункцию в условиях экспериментальной артериальной гипертонии

Длительное (в течение 2 недель) стрессирование с заменой питьевой воды на 1,8 % раствор NaCl вызывает развитие артериальной гипертонии (АГ) у животных, о чем свидетельствует повышение систолического и диастолического артериального давления (САД и ДАД) на 7 и 14 день наблюдения на 18,7 и 21,7 %, и 21,5 и 24,6 % (p < 0,05), соответственно, относительно исходных данных. АГ способствует развитию эндотелиальной дисфункции, на что указывает нарушение эндотелийзависимой вазодилатации, гиперкоагуляция, увеличение степени и скорости агрегации тромбоцитов на 34,5 и 36,6 %, повышение уровня С-реактивного белка (СРБ), фактора Виллебранда (фВ) в 1,5 и 2 раза, соответственно, по сравнению с контрольной группой интактных животных (p < 0,05). Густой экстракт из травы первоцвета весеннего (ГЭТПВ), вводимый животным внутрижелудочно 1 раз в сутки до стрессирования в дозе 60 мг/кг, предупреждал повышение САД и ДАД на 7 и 14 сут эксперимента сопоставимо с препаратами сравнения небивололом и раунатином. ГЭТПВ улучшал эндотелийзависимую вазодилатацию, оказывал антиагрегантное действие, снижая степень и скорость агрегации тромбоцитов на 23,7 и 27,3 % (p < 0,05), соответственно, концентрация фВ у крыс, получавших препарат, была в 2,2 раза ниже, чем в контрольной группе животных (p < 0,05).

Experimental Models Used in Hypertension Research

Hypertension is the most important risk factor for cardiovascular diseases such as stroke, coronary artery disease and sudden cardiac death. Depending on the etiology, there are many different hypertension types, these types of hypertension are investigated in different models.The use of experimental animal models has provided valuable information on many aspects of hypertension such as etiology, pathophysiology, complication and treatment. For this purpose, appropriate experimental method and animal to be used in these studies should be selected considering the design of the study and its limitations. Since significant differences exist between hypertension in experimental animals and human hypertension the extrapolation of results obtained from experimental studies to humans is extremely important. In this review, various experimental models which are used in hypertension research were evaluated.

Hypertension: An Immune Disorder?

T cell depletion can prevent hypertension in experimental animals. What is the nature of Tcell activation in hypertension? In this issue of Immunity, Carnevale etal. (2014) implicate PlGF signaling in a reservoir of splenic Tcells.

Salt-sensitive hypertension in mitochondrial superoxide dismutase deficiency is associated with intra-renal oxidative stress and inflammation

Renal interstitial inflammation and oxidative stress are invariably present and play a key role in the pathogenesis of hypertension in experimental animals. Mitochondria are the major source of reactive oxygen species (ROS). ROS generated in the mitochondria are normally contained by the mitochondrial antioxidant system including manganese superoxide dismutase (MnSOD). We have previously shown that a high salt diet causes hypertension in MnSOD-deficient (MnSOD(+/-)) mice but not in wild-type mice. The present study was undertaken to determine the effect of a high salt diet on oxidative and inflammatory pathways in the kidneys of MnSOD(+/-) mice compared to the wild-type mice. Wild-type (MnSOD(+/+)) and MnSOD(+/-) mice were randomized to receive a regular or a high salt diet for 4 months. Tail arterial pressure was measured and timed urine collection was obtained. The animals were then euthanized and the kidneys were harvested and processed for histological examination and Western blot analyses. In confirmation of our earlier study, a high salt diet resulted in a significant rise in arterial pressure and urinary albumin excretion in MnSOD(+/-) mice. This was accompanied by upregulation of NAD(P)H oxidase subunits, activation of nuclear factor kappa B, and elevation of PAI-1, iNOS, oxidized LDL receptor, and CD36 in the kidneys of the MnSOD(+/-) mice fed the high salt diet. In contrast, consumption of a high salt diet did not significantly alter blood pressure, urine protein excretion, or the measured oxidative and inflammatory mediators in the wild-type mice. Salt-induced hypertension in MnSOD(+/-) mice is associated with activation of intra-renal inflammatory and ROS generating pathways.

Sustained therapeutic hypercapnia attenuates pulmonary arterial Rho-kinase activity and ameliorates chronic hypoxic pulmonary hypertension in juvenile rats

Sustained therapeutic hypercapnia prevents pulmonary hypertension in experimental animals, but its rescue effects on established disease have not been studied. Therapies that inhibit Rho-kinase (ROCK) and/or augment nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling can reverse or prevent progression of chronic pulmonary hypertension. Our objective in the present study was to determine whether sustained rescue treatment with inhaled CO(2) (therapeutic hypercapnia) would improve structural and functional changes of chronic hypoxic pulmonary hypertension. Spontaneously breathing pups were exposed to normoxia (21% O(2)) or hypoxia (13% O(2)) from postnatal days 1-21 with or without 7% CO(2) (Pa(CO(2)) elevated by ∼25 mmHg) or 10% CO(2) (Pa(CO(2)) elevated by ∼40 mmHg) from days 14 to 21. Compared with hypoxia alone, animals exposed to hypoxia and 10% CO(2) had significantly (P < 0.05) decreased pulmonary vascular resistance, right-ventricular systolic pressure, right-ventricular hypertrophy, and medial wall thickness of pulmonary resistance arteries as well as decreased lung phosphodiesterase (PDE) V, RhoA, and ROCK activity. Rescue treatment with 10% CO(2), or treatment with a ROCK inhibitor (15 mg/kg ip Y-27632 twice daily from days 14 to 21), also increased pulmonary arterial endothelial nitric oxide synthase and lung NO content. In contrast, cGMP content and cGMP-dependent protein kinase (PKG) activity were increased by exposure to 10% CO(2), but not by ROCK inhibition with Y-27632. In vitro exposure of pulmonary artery smooth muscle cells to hypercapnia suppressed serum-induced ROCK activity, which was prevented by inhibition of PKG with Rp-8-Br-PET-cGMPS. We conclude that sustained hypercapnia dose-dependently inhibited ROCK activity, augmented NO-cGMP-PKG signaling, and led to partial improvements in the hemodynamic and structural abnormalities of chronic hypoxic PHT in juvenile rats. Increased PKG content and activity appears to play a major upstream role in CO(2)-induced suppression of ROCK activity in pulmonary arterial smooth muscle.

Перекисное окисление липидов и состояния ферментативной антиоксидантной системы при экспериментальной гипертензии у животных с аллергическим увеитом в условиях примененения липофлавона и ацетилцистеина

Перекисное окисление липидов и состояния ферментативной антиоксидантной системы при экспериментальной гипертензии у животных с аллергическим увеитом в условиях примененения липофлавона и ацетилцистеина

Состояние энзиматической антиоксидантной системы в тканях глаза при экспериментальной гипертензии у животных с аллергическим увеитом

Состояние энзиматической антиоксидантной системы в тканях глаза при экспериментальной гипертензии у животных с аллергическим увеитом

Advancing systems medicine and therapeutics through biosimulation

This Interface Focus issue presents 15 different facets of the research conducted by the participants of the BioSim Network (www.biosim-network.net). BioSim was a network of excellence under the Life Sciences, Genomics and Biotechnology for Health Thematic Priority Area of the 6th European Framework Programme. The immediate goal of the network was to develop modelling and simulation approaches that can help the pharmaceutical industry achieve a more rational drug development process. In a broader perspective, the network aimed at contributing in an essential manner to the development of an integrated and quantitative understanding of biological processes. It included a total of 40 partners, including 26 academic research groups from various universities, nine SMEs and Novo Nordisk, with many of the partners having strong collaborations with the pharmaceutical industry. The network established a platform for very fruitful interdisciplinary collaboration with biological groups providing insights into genetics, biochemistry, cellular biology, pharmacology, endocrinology, neurology and physiology; clinicians and hospital groups bringing experience in treatments of depression, various forms of tremor, and cancer clinical interventions and theoreticians providing expertise in bioinformatics, systems biology (SB), network theory, statistical physics, nonlinear dynamics and complex systems theory, as well as pharmacokinetics and clinical trial planning.

Chronic Angiotensin II Infusion Causes Differential Responses in Regional Sympathetic Nerve Activity in Rats

Angiotensin II (AngII)-induced hypertension in experimental animals has been proposed to be attributed in part to activation of the sympathetic nervous system. This sympathetic activation appears to be accentuated in animals consuming a high-salt diet (AngII-salt hypertension). However, accurate quantification of sympathetic activity is difficult, and controversy remains. It is particularly important to ask which are the critical vascular beds targeted by increased sympathetic nerve activity (SNA) in AngII-salt hypertension. To address this issue, mean arterial pressure and renal SNA or lumbar SNA were continuously recorded during a 5-day control period, 11 days of AngII (150 ng/kg per minute, SC), and a 5-day recovery period in conscious rats on a high-salt (2% NaCl) diet. Although mean arterial pressure reached a new steady-state level of 30 to 35 mm Hg above control levels by the end of the AngII period, renal SNA decreased by 40% during the first 7 days of AngII and then returned toward control levels by day 10 of AngII. In contrast, lumbar SNA remained at control levels throughout the AngII period. In another experiment we measured hindlimb norepinephrine spillover in conscious rats on normal (0.4%) or high- (2.0%) salt diets before and during 14 days of AngII administration. AngII had no significant affect on hindlimb norepinephrine spillover in either group. We conclude that chronic AngII modulates renal and lumbar SNAs differentially in rats consuming a high-salt diet and that AngII-salt hypertension in the rat is not caused by increased SNA to the renal or hindlimb vascular beds.

Akira Takeshita, MD, PhD

Akira Takeshita, MD, PhD, 69, Professor Emeritus of Cardiovascular Medicine and Director Emeritus of the Institute of Angiocardiology, Kyushu University Graduate School of Medicine, Japan, died on March 15, 2009 after a long illness. Dr Takeshita was an internationally recognized leader in cardiovascular medicine. His research focused on neural regulation and vascular biology. Dr Takeshita was born on January 24, 1940. He earned his MD degree from Kyushu University School of Medicine in 1965. His unique and international career started immediately after his graduation when, unlike many other Japanese physicians, especially at that time, he moved to the Tachikawa U.S. Air Force Hospital near Tokyo, where he was an intern and resident. He met Makiko, who was performing her externship in anesthesiology at the Hospital, and they married in 1968. They helped each other as the best partners in life and also as medical professionals, for 41 years until his death. In 1967, Dr Takeshita returned to Kyushu University where he trained in the Department of Cardiovascular Medicine. He then moved to Mount Sinai Hospital, Cleveland, in …

Abstract 2517: Presence of Auto-antibody against Angiotensin II Receptor in Pregnant Women and Its Potential Role in the Development of Preeclampsia

Preeclampsia is a serious pathologic complication during pregnancy but its pathogenesis remains unclear. We recently demonstrated that production of auto-antibody against angio-tensin (AGN) II type I receptor (AT1-AA) causes hypertension in experimental animals. Current study determined whether AT1-AA is present in pregnant women and if so, to investigate its potential role in the development of preeclampsia. Blood samples were collected from 35 pregnant women (preeclampsia=18, control=17) and AT1-AA was detected. To determine the potential mechanisms by which AT1-AA may contribute to the development of preeclampsia, vasoconstrictive effects of purified AT1-AA was determined in isolated rat arteriae cerebri media and its pro-apoptotic and cytotoxic effect was determined in cultured HUVEC. Compared with the normal pregnant women (week 37 to 39), sera levels of AT1-AA were markedly increased in preeclamptic patients (0.27±0.03 μmol/L vs. 0.023±0.017 μmol/L, P&lt;0.01). In isolated resistant vascular rings, AT1-AA at pathologically relevant concentrations (0.1 to 0.5 μmol/L) caused significant vasoconstriction (P&lt;0.01) which was completely blocked by losartan, an AT1-receptor antagonist. These results demonstrated that the AT1-AA causes vascular constriction though activation of AT1-receptor. Moreover, in vitro incubation of HUVEC with AT1-AA (0.5 μmol/L, 48 hours) resulted in significant caspase activation (caspase-3 and caspase-8: 0.69±0.14 and 3.54±0.24 nmol/h/mg protein with AT1-AA vs. 0.02±0.02 and 0.95±.28 nmol/h/mg protein with normal sera, P&lt;0.01) and a &gt;2-fold increase in LDH release (P&lt;0.01). The pro-apoptotic and cytotoxic effect of AT1-AA was almost identical with that seen in AGN II-treated HUVEC. Collectively, current study demonstrated that AT1-AA is markedly increased in preeclamptic patients. More importantly, purified AT1-AA not only has a direct vasoconstrictive effect which increases blood pressure, but also causes significant endothelial cell death that indirectly contributes to the development of hypertension. These results suggest that production of AT1-AA is a novel risk factor in pregnant women and this auto-antibody may play a causative role in the development of preeclampsia.

Circulating angiotensin II attenuates the sympathetic baroreflex by reducing the barosensitivity of medullary cardiovascular neurones in the rat.

Chronic intravenous angiotensin II (Ang II) has been widely used to establish centrally mediated hypertension in experimental animals, and disruption of Ang II activity is a frontline treatment for hypertensive disease. However, the acute central actions of circulating Ang II are poorly understood. We examined the effects of intravenous pressor doses of Ang II on autonomic activity in anaesthetized rats under neuromuscular blockade, and compared baroinhibition evoked by Ang II pressor ramps to equipressor responses evoked by phenylephrine (PE). Baroinhibition of splanchnic sympathetic nerve activity was attenuated during Ang II trials compared with PE, and rats remained sensitive to electrical stimulation of the aortic depressor nerve at higher arterial pressures during Ang II trials. This was not due to a direct effect of Ang II on aortic nerve baroreceptors. In a separate series of experiments, we provide direct evidence that bulbospinal barosensitive neurones in the rostral ventrolateral medulla are differentially sensitive to pressure ramps evoked by Ang II or PE vasoconstriction. Nineteen out of 41 units were equally sensitive to increased arterial pressure evoked by Ang II or PE. In 17 of 41 units, barosensitivity was attenuated during Ang II trials, and in five of 41 cases units that had previously been barosensitive increased their firing rate during Ang II trials. These results show, for the first time, that circulating Ang II acutely modulates central cardiovascular control mechanisms. We suggest that this results from activation by Ang II of a central pathway originating at the circumventricular organs.

Hypothesis

Phospholipids from the group B streptococcal (GBS) cell wall cause pulmonary hypertension in experimental animals. When exposed to penicillin, Streptococcus mutans releases phospholipids immediately. We hypothesize that newborns colonized with GBS receive bacterial phospholipids leading to pulmonary hypertension and respiratory distress, especially in the situation of newborns of penicillin-treated mothers. We examined clinical and epidemiologic data on these relations. We used data from a prospective multicenter GBS study conducted from 1995 to 1999 in which 1674 of 17,690 newborns cultured at 4 sites were colonized with GBS. Our analyses included 1610 colonized newborns > or =32 weeks gestation without early-onset disease. Clinical features were compared between 1003 lightly colonized (GBS positive at < or =2 sites) and 607 heavily colonized (positive at 3 or 4 sites) newborns. The rates of respiratory distress were compared between colonized newborns of penicillin-treated mothers and those of untreated mothers. Of the 1610 colonized newborns, 8.8% had signs of respiratory distress within 48 hours after birth (cases). Oxygen supplementation was used in 60% of the cases, mechanical ventilation was required in 5% and persistent pulmonary hypertension was diagnosed in 2%. Compared with light colonization, heavy colonization increased the rate of respiratory distress 1.73-fold (95% CI, 1.26-2.38), a discharge diagnosis of respiratory disorder 2.02-fold (95% CI, 1.16-3.52), a blood/cerebrospinal fluid obtained for culture 1.54-fold (95% CI, 1.24-1.93) and antibiotic administration after birth 1.87-fold (95% CI, 1.34-2.61). Penicillin use during labor was associated with a 2.62-fold (95% CI, 1.79-3.83) increase in respiratory distress in the colonized newborn. Our findings support the association of neonatal respiratory distress with asymptomatic GBS colonization and with penicillin use during labor. These data require confirmation.

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.

Early and Sustained Inhibition of Nuclear Factor-κB Prevents Hypertension in Spontaneously Hypertensive Rats

Compelling evidence has emerged pointing to the interaction of oxidative stress and renal interstitial inflammation and their mutual contribution to the pathogenesis of hypertension in experimental animals. Renal interstitial inflammation in spontaneously hypertensive rats (SHR) is accompanied by and largely due to activation of redox-sensitive, proinflammatory nuclear transcription factor-kappaB (NF-kappaB). Therefore, the present study was designed to test the hypothesis that long-term inhibition of NF-kappaB, beginning early in the course of the disease, may attenuate renal interstitial inflammation and hypertension in SHR. To this end, we administered the reputed NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) (100 mg/kg daily intraperitoneally) to SHR from 7 to 25 weeks of age and compared the results with vehicle-treated SHR. Vehicle-treated and PDTC-treated Wistar Kyoto (WKY) rats served as controls. The untreated SHR exhibited a significant rise in arterial pressure; increased NF-kappaB activation, elevated intercellular adhesion molecule (ICAM)-1 and in situ mRNA macrophage chemoattractant molecule-1 (MCP-1) expressions; and interstitial accumulation of lymphocytes, macrophages, and angiotensin-II-positive cells. PDTC administration prevented the rise in blood pressure, and normalized renal cortical NF-kappaB activity as well as ICAM-1 and MCP-1 expressions. This was accompanied by a significant reduction in infiltration of immune cells, angiotensin II-expressing cells, and renal tissue malondialdehyde content to values that matched those found in the control WKY rats. Results suggest that NF-kappaB-driven intrarenal inflammatory reactivity play a major role in the pathogenesis of hypertension in the SHR.

Vascular Endothelin and Hypertension - From Receptors to Medicine

The last two decades have witnessed great advances in our understanding of the role of the vascular endothelin (ET) system in the control of blood pressure. The role of ET as one of the most potent endothelium-derived vasoconstrictors is now complemented with a newly discovered role in vascular relaxation. The transcription of the ET genes in endothelial cells leads to the formation of preproET and big ET, which are further metabolized by ET converting enzymes into ET-1, -2, -3 and -4 isoforms. ET isoforms bind with different affinities to ETA and ETB2 receptors in vascular smooth muscle, and stimulate [Ca2+]i and other signaling mechanisms of smooth muscle contraction and growth. ET also binds to endothelial ETB1 receptors, which are coupled to increase production of vasodilator substances such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and may also function in ET clearance. Despite the prominent effects of ET on vascular function and growth, the role of ET and its receptors in the regulation of blood pressure and in the pathogenesis of hypertension has not been clearly established. Some forms of moderate to severe hypertension in human and salt-dependent hypertension in experimental animals may show elevated levels of plasma or vascular ET; however, other forms of hypertension may show normal levels. Also, while ET antagonists could reverse some forms of experimental hypertension, their potential use in medicine needs to be carefully examined particularly with regard to their effectiveness and specificity.

Excess l-arginine restores endothelium-dependent relaxation impaired by monocrotaline pyrrole

The pyrrolizidine alkaloid plant toxin monocrotaline pyrrole (MCTP) causes pulmonary hypertension in experimental animals. The present study aimed to examine the effects of MCTP on the endothelium-dependent relaxation. We constructed an in vitro disease model of pulmonary hypertension by overlaying MCTP-treated bovine pulmonary artery endothelial cells (CPAEs) onto pulmonary artery smooth muscle cell-embedded collagen gel lattice. Acetylcholine (Ach) induced a relaxation of the control CPAEs-overlaid gels that were pre-contracted with noradrenaline, and the relaxation was inhibited by L-NAME, an inhibitor of NO synthase (NOS). In contrast, when MCTP-treated CPAEs were overlaid, the pre-contracted gels did not show a relaxation in response to Ach in the presence of 0.5 mM l-arginine. Expression of endothelial NOS protein, Ach-induced Ca 2+ transients and cellular uptake of l-[ 3H]arginine were significantly smaller in MCTP-treated CPAEs than in control cells, indicating that these changes were responsible for the impaired NO production in MCTP-treated CPAEs. Since cellular uptake of l-[ 3H]arginine linearly increased according to its extracellular concentration, we hypothesized that the excess concentration of extracellular l-arginine might restore NO production in MCTP-treated CPAEs. As expected, in the presence of 10 mM l-arginine, Ach showed a relaxation of the MCTP-treated CPAEs-overlaid gels. These results indicate that the impaired NO production in damaged endothelial cells can be reversed by supplying excess l-arginine.