Angiotensin II enhances responses to endothelin-1 in bovine bronchial smooth muscle

Altered renin-angiotensin system gene expression in airways of antigen-challenged mice: ACE2 downregulation and unexpected increase in angiotensin 1-7

OBJECTIVE

Evidence suggest that the renin-angiotensin system (RAS) is activated in people with asthma, although its pathophysiological role is unclear. Angiotensin-converting enzyme 2 (ACE2) is the major enzyme that converts angiotensin II to angiotensin 1-7 (Ang-1-7), and is also known as a receptor of SARS-CoV-2. The current study was conducted to identify the change in RAS-related gene expression in airways of a murine asthma model.

METHODS

The ovalbumin (OA)-sensitized mice were repeatedly challenged with aerosolized OA to induce asthmatic reaction. Twenty-four hours after the last antigen challenge, the main bronchial smooth muscle (BSM) tissues were isolated.

RESULTS

The KEGG pathway analysis of differentially expressed genes in our published microarray data revealed a significant change in the RAS pathway in the antigen-challenged mice. Quantitative RT-PCR analyses showed significant increases in the angiotensin II-generating enzymes (Klk1, Klk1b3 and Klk1b8) and a significant decrease in Ace2. Surprisingly, ELISA analyses revealed a significant increase in Ang-1-7 levels in bronchoalveolar lavage (BAL) fluids of the antigen-challenged animals, while no significant change in angiotensin II was observed. Application of Ang-1-7 to the isolated BSMs had no effect on their isometrical tension.

CONCLUSION

The expression of Ace2 was downregulated in the BSMs of OA-challenged mice, while Klk1, Klk1b3 and Klk1b8 were upregulated. Despite the downregulation of ACE2, the level of its enzymatic product, Ang-1-7, was increased in the inflamed airways, suggesting the existence of an unknown ACE2-independent pathway for Ang-1-7 production. The functional role of Ang-1-7 in the airways remains unclear.

Pulmonary artery targeted therapy in treatment of COVID-19 related ARDS. Literature review

INTRODUCTION

The most grievous complication of the COVID-19 is the acute respiratory distress syndrome. A specific, rescue treatment for rapidly deteriorating patients should emerge to improve respiratory function and help patients to survive the most challenging period. Drugs used in targeted therapy of pulmonary arterial hypertension (PAH) appears to be suitable for this task and this article describes their potential for treatment of severe cases of COVID-19.

METHODS

The authors reviewed the following databases for randomized controlled trials, reviews and meta-analyses published up to July 2020: Pubmed, Scopus, Google Scholar, Cochrane Database and ClinicalKey. The authors included every study contributory to the assessment of the potential of drugs used in targeted PAH therapy in treatment of COVID-19.

RESULTS

Endothelin receptor antagonists, phosphodiesterase 5 inhibitors, riociguat and prostacyclin have proven ani-inflammatory effect and reduce pulmonary artery blood pressure, lung oedema and remodelling. Bosentan shows antiviral properties and sildenafil, as well as epoprostenol, inhibits apoptosis of lung epithelial cells. Among patients with lung lesions the decrease of pulmonary blood pressure can lead to increase of ventilation/perfusion mismatch and decrease of blood oxygenation.

CONCLUSIONS

Among all assessed drugs bosentan, sildenafil and epoprostenol appear to be most promising and a combination of these drugs should be considered due to synergism. The targeted PAH therapy in treatment of COVID-19 associated ARDS could be a useful tool saving lives of patients with severe SARS-CoV-2 infection, however, its introduction should be investigated and monitored very carefully as it can lead to transient deterioration of patient condition.

All-Trans Retinoic Acid Exerts Neuroprotective Effects in Amyotrophic Lateral Sclerosis-Like Tg (SOD1*G93A)1Gur Mice

All-trans retinoic acid (ATRA), a ligand of retinoic acid receptors, could regulate various biological processes by activating retinoic acid signals. Recent studies suggested that ATRA displays multiple neuroprotective effects and thereby alleviates the disease progression in a variety of neurological diseases. Our previous studies found that the impaired retinoic acid signal decreased ALDH1A2, an essential synthetase of ATRA, in the spinal cord of ALS mice. Here, we evaluated the neuroprotective and neurorestorative effects of ATRA in a SOD1-G93A transgenic mice model of ALS. We administrated ATRA(3 mg/kg) daily from the onset stage to the progression stage for 5 weeks. Behavioral tests showed that ATRA improved the forelimb grip strength in ALS mice and may slow the disease progression, but not the body weight. ATRA could completely reverse the impaired retinoic acid receptor alpha (RARα) signal in the spinal cord of ALS mice. This effect was accompanied by enhancing the degradation of misfolded proteins via the ubiquitin-proteasome system, regulating the oxidative stress, inhibiting the astrocyte activation, and promoting the neurotrophic signal recovery. Our findings are the first to indicate that the damaged retinoic acid signal is involved in the pathogenesis of ALS, and ATRA could induce the functional neuroprotection via repairing the damaged retinoic acid signal.

All trans-retinoic acid protects against acute ischemic stroke by modulating neutrophil functions through STAT1 signaling

Background and purpose

Regulation of neural inflammation is considered as a vital therapeutic target in ischemic stroke. All-trans retinoic acid (atRA), a potent immune modulator, has raised interest in the field of stroke therapy. However, the immunological mechanisms for atRA-mediated neuroprotection remain elusive. The current study evaluated the impact of atRA on post-stroke neural inflammation and elucidated the mechanisms involved in the regulation of related neutrophil functions.

Methods

atRA was prophylactically administered to mice 1 day before transient middle cerebral artery occlusion (tMCAO, 1 h) and repeated daily immediately after reperfusion for 3 days. Stroke outcomes, neutrophil polarization, and formation of neutrophil extracellular traps (NETs) in the stroke lesion were assessed. Neutrophil depletion was induced with anti-Ly6G antibodies. Primary neutrophil cultures were used to explore the mechanisms of atRA treatment.

Results

Prophylactic atRA treatment reduced infarct volumes and neurological deficits at 1 day after tMCAO. Post-stroke neural inflammation was attenuated and neutrophil accumulation in lesion was downregulated. atRA treatment skewed neutrophil toward N2 phenotype which facilitated its clearance by macrophage and inhibited NETs formation. The functions of neutrophil were indispensable in the protective effects of atRA and were associated with suppression to STAT1 signaling by atRA. Administration of atRA after stroke still provided efficient protection to cerebral ischemia.

Conclusion

atRA displays potent therapeutic efficacy in ischemic stroke by attenuating neural inflammation. Treatment of atRA impeded neutrophil accumulation, favored N2 polarization, and forbade NETs formation in ischemic lesion. STAT1 signaling played a decisive role in the mechanisms of atRA-afforded regulation to neutrophil.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1557-6) contains supplementary material, which is available to authorized users.

The potential effect of the angiotensin II receptor blocker telmisartan in regulating OVA-induced airway remodeling in experimental rats

BACKGROUND

Bronchial asthma is a true ascending clinical problem. Angiotensin II is now accused to be potentially implicated in its pathogenesis, being a potent pro-inflammatory mediator with remodeling effects.

OBJECTIVE

This study aims to evaluate the possible protective effect of telmisartan, an angiotensin II receptor blocker, on experimentally-induced bronchial asthma.

METHODS

Animals were divided into 5 groups; a normal control group, an asthma control group, a reference treatment group, receiving dexamethasone, and two treatment groups, receiving telmisartan in two dose levels. Bronchial asthma was induced by intraperitoneal sensitization followed by intranasal challenge with ovalbumin (OVA). Test agents were administered prior to each intranasal OVA challenge. Lung function tests, namely tidal volume (TV) and peak expiratory flow rate (PEF) were assessed 1h after the last challenge. One day after the last challenge, absolute eosinophil counts (AEC) in blood and bronchoalveolar lavage fluids (BALF) were assessed. Serum immunoglobulin E (IgE) as well as BALF total nitrate/nitrite (NOx) were assessed. Oxidative and inflammatory biomarkers, namely lung tissue superoxide dismutase (SOD), glutathione reduced (GSH), tumor necrosis factor-alpha (TNF-α) and interleukin-5 (IL-5), were also assessed, in addition to histopathological study.

RESULTS

Telmisartan administration in both doses significantly improved TV, PEF, AEC, IgE, NOx, GSH, SOD, TNF-α and IL-5 values compared to asthma control values. Histopathological study strongly supported the results of biochemical estimations, particularly regarding airway remodeling.

CONCLUSION

These results suggest that telmisartan may have potential protecting effects against experimental bronchial asthma, probably due to its bronchodilator, antioxidant and anti-inflammatory effects.

Association of the variants in AGT gene with modified drug response in Korean aspirin-intolerant asthma patients

The angiotensinogen (AGT) gene enhances the effect of several bronchoconstrictors and produces a peptide that is accumulated in the airways of asthma patients; events that may underpin the pathogenesis of aspirin-intolerant asthma (AIA). To carry out a case-control analysis between AGT and aspirin-induced bronchospasm following treatment with an anti-asthma drug, montelukast (MLK), 38 single nucleotide polymorphisms (SNPs) in AGT were genotyped in 56 AIA cohort. Genotyping was performed with TaqMan assay and haplotypes were inferred using PHASE algorithm ver. 2.0. Statistical analyses of each SNPs and haplotypes were performed using SAS version 9.1. Among 13 variants displaying significant signals, two SNPs (+2401C>G and +2476C>T) in the intronic region of AGT were significantly associated with modification of drug response even after correction for multiple testing (P=0.0009-0.002; P(corr)=0.02-0.03). Furthermore, the two variants also exhibited associations with MLK response rate (P=0.0003-0.0006; P(corr)=0.006-0.01). Although our results are preliminary and further replication in a larger-scale group of subjects should be warranted, these observations provide evidence that AGT variants might be one of genetic factors involved in the response of anti-asthma drugs in AIA patients.

Involvement of Src family kinase activation in angiotensin II-induced hyperresponsiveness of rat bronchial smooth muscle

Angiotensin II (Ang II) might be an important mediator in pathogenesis of airway hyperresponsiveness (AHR) that is the asthmatic characteristic feature of asthma, although the mechanisms of AHR caused by Ang II are not yet clear. Presently, the RT-PCR analyses revealed that all the Src family kinases (SFKs), such as Fyn, Lck, Lyn, Hck, Src, Yes, Blk, Fgr and Frk, were expressed in the lungs and main bronchi of rats. The phosphorylation (activation) of SFK (Tyr416) was increased in bronchial smooth muscle (BSM) by Ang II. The Ang II-induced SFK phosphorylation was inhibited by pretreatment with SU6656, an SFK inhibitor. The concentration-contraction curves to carbachol (CCh) were shifted to the left in the presence of Ang II. The maximal contraction of CCh was also significantly increased by pretreatment with Ang II. These results indicate that Ang II causes BSM hyperresponsiveness. The Ang II-induced BSM hyperresponsiveness was significantly inhibited by SU6656, although the carbachol (CCh)-induced contraction itself was not changed by SU6656. In conclusion, Ang II induced a BSM hyperresponsiveness through activation of SFK, and might play an important role in pathophysiology of bronchial asthma.

Angiotensin II induces hyperresponsiveness of bronchial smooth muscle via an activation of p42/44 ERK in rats

Angiotensin II (Ang II) might be an important mediator in the pathogenesis of bronchial asthma, although the mechanisms of airway hyperresponsiveness caused by Ang II are not yet clear. Whether p42/44 ERK contributes to the Ang II-elicited bronchial smooth muscle (BSM) hyperresponsiveness in rats was presently examined. The RT-PCR analyses revealed that Ang II AT(1A), AT(1B), and AT(2) receptors, angiotensinogen, angiotensin-converting enzyme, but not renin, were expressed in the lungs, trachea, and main bronchi of rats. Only a small and transient contraction was induced by the application of Ang II in the main bronchial smooth muscle; the contraction was inhibited by losartan, an AT(1) receptor antagonist. The contractions induced by carbachol (CCh), high K(+) depolarization, and sodium fluoride (NaF; a G protein activator) were augmented by pretreatment with Ang II. The BSM hyperresponsiveness induced by Ang II was abolished by losartan. Furthermore, the Ang II-induced BSM hyperresponsiveness to CCh was attenuated by pretreatment with U-0126, a p42/44 ERK kinase (MEK-1/2) inhibitor. In conclusion, Ang II-induced BSM hyperresponsiveness through the activation of p42/44 ERK may play an important role in the pathophysiology of bronchial asthma, although Ang II itself caused a small force development in the bronchial smooth muscle.

Effect of candesartan, a type 1 angiotensin II receptor antagonist, on bronchial hyper-responsiveness to methacholine in patients with bronchial asthma

AIMS

Angiotensin II is a putative mediator in bronchial asthma. There have been very few studies investigating the involvement of angiotensin II receptors in bronchial hyper-responsiveness in asthmatic patients. We examined the effect of candesartan cilexetil, a specific angiotensin II type 1 (AT1) receptor antagonist, on bronchial responsiveness to inhaled methacholine in patients with asthma.

METHODS

Bronchial responsiveness to methacholine, assessed as the concentration of methacholine producing a 20% fall in FEV1 (PC20-FEV1), was measured on three occasions 2 weeks apart in 11 stable asthmatic patients. Candesartan cilexetil (8 mg once a day) or a placebo was orally administered for 1 week before the methacholine provocation test in a double-blind, randomized, crossover manner.

RESULTS

Although there were no significant differences between treatment periods in FEV1 values at baseline, the geometric mean (95% CI) PC20-FEV1 values increased significantly (P = 0.041) from 0.691 (0.379, 1.259) mg ml-1 with placebo to 0.837 (0.506, 1.384) mg ml-1 with candesartan. Candesartan decreased the mean (95% CI) arterial blood pressure (placebo: 95.6 (89.0, 102.2) mmHg, candesartan: 86.4 (79.8, 93.1) mmHg, P = 0.015). There was no correlation between the change in blood pressure and the change in PC20-FEV1.

CONCLUSIONS

We conclude that AT1 receptors are involved in bronchial hyper-responsiveness in asthmatic patients.

Endothelin-A receptor antagonist inhibits angiotensin II and noradrenaline in man

AIMS

Endothelin-1 (ET-1) is a potent vasoconstrictor produced by the vascular endothelium. The interactions of ET with the mediators of the sympathetic nervous system and the renin-angiotensin-system in humans are unclear.

METHODS

We studied the effects of the ETA-selective antagonist BQ-123 and the ETB-selective antagonist BQ-788 (both 10(-10)-10(-8) M) on ET-1 (10(-16)-10(-10) M), angiotensin II (AT, 10(-16)-10(-10) M) and noradrenaline (NA, 10(-16)-10(-10) M) induced vasoconstriction in the human skin microcirculation in vivo in 25 healthy male volunteers using laser Doppler flowmetry and double injection technique.

RESULTS

BQ-123 caused a dose-dependent vasodilatation (maximum effect: + 949 +/- 84 AUC-PU, P < 0.001), whereas BQ-788 induced mild vasoconstriction (maximum effect: -388 +/- 96 AUC-PU, P < 0.01). In the presence of BQ-123, but not BQ-788, ET-1, AT and NA caused markedly less vasoconstriction at any tested agonist dose; the effect was most pronounced on ET-1 (maximum effect at 10(-14) M: + 814 +/- 93 AUC-PU vs ET alone, P < 0.001), followed by noradrenaline (maximum effect at 10(-16) M: +580 +/- 107 AUC-PU vs NA alone, P < 0.01) and angiotensin II (maximum effect at 10(-14) M: + 493 +/- 111 AUC-PU vs AT alone, P < 0.001).

CONCLUSIONS

ETA-selective antagonism inhibits vasoconstriction to AT and NA in vivo in healthy subjects. This beneficial effect may be useful for the treatment of patients with cardiovascular disease including hypertension especially in combination therapy with sympatholytic agents and inhibitors of the renin-angiotensin system.

Effect of losartan, a type 1 angiotensin II receptor antagonist, on bronchial hyperresponsiveness to methacholine in patients with bronchial asthma

It is unclear whether angiotensin II receptors are involved in bronchial hyperresponsiveness in asthmatic patients. We examined the effect of losartan, a specific angiotensin II type 1 (AT1) receptor antagonist, on bronchial responsiveness to inhaled methacholine in eight patients with stable asthma. Bronchial responsiveness to methacholine, assessed as the concentration of methacholine producing a 20% fall in FEV(1) (PC(20)-FEV(1)) and a 35% fall in standardized partial expiratory flow at 40% of FVC (PC(35)-PEF(40)), was measured on two occasions 2 wk apart. Losartan (50 mg once a day) or a placebo was orally administered for 1 wk before methacholine provocation test in a double-blind, randomized, crossover fashion. Although the PC(20)-FEV(1) values after placebo (2.037 [geometric standard error of the mean, GSEM = 0.210] mg/ml) and losartan (2.098 [GSEM, 0.239] mg/ml) were identical (p = 0.840), the geometric mean PC(35)-PEF(40) values significantly (p = 0.034) increased from 0.258 (GSEM, 0.156) mg/ml with placebo to 0.456 (GSEM, 0.186) mg/ml with losartan. We conclude that AT1 receptors are involved in bronchial hyperresponsiveness in asthmatic patients. This is the first report demonstrating the involvement of AT1 receptors in bronchial asthma.

Type 1 angiotensin II receptor antagonism reduces antigen-induced airway reactions

Although the renin-angiotensin system is activated in patients with asthma during severe acute attacks and angiotensin II has been shown to cause bronchoconstriction in patients with asthma, the role of angiotensin II in patients with asthma is unclear. We investigated the effects of two specific antagonists at type 1 and type 2 angiotensin II receptors, candesartan cilexetil (TCV-116) and PD123319, on antigen-induced airway reactions in guinea pigs. Sixty minutes after intraperitoneal administration of candesartan cilexetil (0.1, 1.0, or 10 mg/kg) or PD123319 (30 mg/kg), animals received an antigen challenge. Airway responsiveness to inhaled methacholine was assessed as the dose of methacholine required to produce a 200% increase in the pressure at the airway opening (PC(200)). Differential cell counts in bronchoalveolar lavage fluids (BALF) were measured 24 h after antigen challenge. Candesartan cilexetil did not inhibit antigen-induced bronchoconstriction in sensitized guinea pigs or alter PC(200) in nonsensitized guinea pigs. Antigen inhalation significantly increased bronchoconstrictor responses to methacholine and increased airway accumulation of eosinophils; both responses showed dose-dependent prevention by candesartan but not by PD123319. These results indicate that endogenous angiotensin II promotes antigen-induced airway hyperresponsiveness and eosinophil accumulation by acting at type 1 receptors.

Endothelins and the lung

Since endothelins were discovered by Yanasigawa in 1988 it has been recognised that they may have an important role in lung pathophysiology. Despite their biological importance as vasoconstrictors the physiological role of endothelin has not yet been defined within the lungs. This review explores their role in acute and chronic disease. During acute inflammation and ischaemia-reperfusion injury cytokines may induce release of endothelin. This is important in the realm of acute lung injury and during surgical procedures such as cardiopulmonary operations including lung resections and transplantation. Complications of surgery including primary organ failure resulting in poor gas exchange as well as increased pulmonary vascular resistance have been linked to the presence of excessive endothelin. Endothelin may have an important role in transplantation biology. The complex process leading to successful lung transplantation includes optimising the donor with brain death, harvesting the lungs, managing acute and chronic rejection, and protecting the vital organs from toxic effects of immunosuppressants. During chronic disease processes, the mitotic action of endothelin may be important in vascular and airway remodelling by means of smooth muscle cell proliferation. We also explore recent advances in drug development, animal models and future directions for research.

Effect of infused angiotensin II on the bronchoconstrictor activity of inhaled endothelin-1 in asthma

STUDY OBJECTIVES

Endothelin (ET)-1 is a potent bronchoconstrictor, and asthmatics demonstrate bronchial hyperresponsiveness to ET-1 given by inhalation. Angiotensin II (Ang II) is increased in plasma in acute severe asthma, causes bronchoconstriction in asthmatics, and potentiates contractions induced by ET-1 in bovine bronchial smooth muscle in vitro, and contractions induced by methacholine both in vitro and in vivo. We wished to examine any potentiation of the bronchoconstrictor activity of inhaled ET-1 by infused Ang II at subbronchoconstrictor doses.

DESIGN

Double-blind randomized placebo-controlled study.

SETTING

Asthma research unit in university hospital.

PATIENTS

Eight asthmatic subjects with baseline FEV1 88% predicted, bronchial hyperreactivity (geometric mean, concentration of methacholine producing 20% fall, methacholine PC20 2.5 mg/mL), and mean age 37.1 years.

INTERVENTIONS

We examined the effect of subbronchoconstrictor doses of infused Ang II (1 ng/kg/min and 2 ng/kg/min) or placebo on bronchoconstrictor responses to inhaled ET-1 (dose range, 0.96 to 15.36 nmol).

MEASUREMENTS

Oxygen saturation, noninvasive BP, and spirometric measurements were made throughout the study visits. Blood was sampled for plasma Ang II levels at baseline and before and after ET-1 inhalation.

RESULTS

Ang II infusion did not produce bronchoconstriction per se at either dose prior to ET-1 challenge. Bronchial challenge with inhaled ET-1 produced dose-dependent bronchoconstriction, but there was no difference in bronchial responsiveness to ET-1 comparing infusion of placebo with Ang II at 1 ng/kg/min or 2 ng/kg/min (geometric mean, concentration of ET-1 producing 15% fall, 5.34 nmol, 4.95 nmol, and 4.96 nmol, respectively) (analysis of variance, p > 0.05). There was an increase in systolic and diastolic BP at the higher dose of Ang II compared to placebo (mean 136/86 vs 117/75 mm Hg, respectively). Plasma Ang II was elevated following infusion of both doses of Ang II compared to placebo.

CONCLUSIONS

In contrast to the potentiating effect on methacholine-induced bronchoconstriction, Ang II at subbronchoconstrictor doses does not potentiate ET-1-induced bronchoconstriction in asthma.

Endothelin in cardiovascular control: the role of endothelin antagonists

Endothelin (ET) is a potent vasoconstrictor associated with various cardiovascular diseases. ET mediates its effects through ET receptors on vascular smooth muscle cells as well as on the vascular endothelium. Furthermore, a neurotransmitter role for ET has been suggested on the basis of experimental and human in vivo studies. ET antagonists are potent tools for studying the effects of ET and its receptors. They have been widely used in vitro and in experimental models of cardiovascular disease, where ET levels are elevated and reactivity to ET is altered. Promising clinical trials in hypertension, coronary artery disease, and congestive heart failure are discussed in this review. Different forms of renal failure are associated with markedly increased ET levels, and ET antagonists experimentally improve renal function in these models. Extrapolating from experimental and first clinical experience, ET antagonists could be useful in the treatment of hypertension, coronary artery disease, congestive heart failure, and renal failure, especially in combination with other drugs, ie, angiotensin converting enzyme inhibitors. The inhibition of ET-induced stimulation of nociception allows for speculation that ET antagonists might even have analgesic properties.

Losartan reduces constrictor responses to endothelin-1 and the thromboxane A2 analogue in aortic rings from spontaneously hypertensive rats: role of nitric oxide

OBJECTIVE

Our study was designed to investigate whether angiotensin II subtype 1 (AT1) receptors are involved in the constrictor responses evoked by endothelin-1 and the thromboxane A2 analogue U46619 in aortic rings from spontaneously hypertensive rats (SHR), by studying the effect of the AT1 receptor antagonist losartan. In addition, since nitric oxide seems to participate in the mechanism of action of losartan, we studied the effect of the nitric oxide synthesis inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), on the action of losartan.

MATERIALS AND METHODS

Dose-response curves of either endothelin-1 (10(-10) to 10(-7) mol/l) or U46619 (10(-10) to 10(-6) mol/l) were studied in the presence or absence of losartan (10(-5) mol/l) in aortic rings from SHR. Likewise, similar experiments were done in aortic rings pretreated with the nitric oxide synthesis inhibitor, L-NAME (10(-4) mol/l).

RESULTS

Pre-incubation with losartan significantly reduced the contractile response to endothelin-1 compared with control rings, without modifying the value represented by 50% of the maximal response (pD2). The concentration-response curve to U46619 was shifted to the right in the presence of losartan, reducing the pD2 compared with control rings. The presence of captopril (10(-5) mol/l) in the incubation media did not alter the response to either endothelin-1 or U46619. The diminished response to both endothelin-1 and U46619 in the presence of losartan was reversed in L-NAME-pretreated rings.

CONCLUSIONS

Angiotensin II seems to participate in the vasoconstriction induced by both endothelin-1 and the thromboxane A2 analogue through the stimulation of AT1 receptors in SHR aortic rings, because losartan inhibited this effect. Moreover, nitric oxide appears to be involved in this action of losartan.

Effect of angiotensin II on histamine-induced bronchoconstriction in the human airway both in vitro and in vivo

The renin-angiotensin system is activated in acute severe asthma. Angiotensin II causes bronchoconstriction in mild asthmatics and potentiates methacholine-evoked bronchoconstriction both in vitro and in vivo. To evaluate the effect of angiotensin II on histamine-induced bronchoconstriction, human bronchial rings (n = 6) were obtained from lung tissue at thoracotomy and were prepared in organ baths. Contractions were measured isometrically and cumulative concentration-response curves obtained to angiotensin II alone and to histamine in the presence and absence of threshold concentrations of angiotensin II. Eight asthmatic patients with bronchial hyper-reactivity to histamine were challenged with histamine during intravenous infusion of placebo, angiotensin II 1 ng kg-1 min-1 and angiotensin 2 ng kg-1 min-1 administered in a randomized, double-blind fashion, FEV1 was measured prior to, during the infusion and during the histamine challenge. Angiotensin II (3 x 10(-7)M and 10(-6)M) alone evoked small contractions (< 0.25 g) of human bronchi in vitro, but pre-incubation with threshold concentrations of angiotensin II (10(-7)M, 3 x 10(-7)M and 10(-6)M) had no effect on histamine-evoked contractions. In asthmatic patients, angiotensin II alone had no effect on baseline FEV1 at the low levels infused and did not affect the response to nebulized histamine as measured by the PC20 histamine: Geometric mean (range) PC20 histamine (mg ml-1) screening day 3.58 (1.26-7.75), placebo infusion 2.67 (0.89-9.57), angiotensin II 1 ng kg-1 min-1 2.45 (0.42-6.97) and angiotensin II 2 ng kg-1 3.09 (0.8-10.78). It is concluded that, in contrast to its potentiating effect on methacholine-induced bronchoconstriction, angiotensin II has no effect on histamine-evoked bronchoconstriction in human bronchi in vitro or in vivo.

Endothelin-1-induced bronchoconstriction in asthma

Endothelin-1 (ET-1) has been indirectly implicated in the pathophysiology of asthma, and it is a potent bronchoconstrictor both in vitro and by inhalation in animal models in vivo. We examined the effect of inhaled ET-1 on airway tone in comparison with methacholine in eight asthmatics and five healthy volunteers in a double-blind randomized fashion. After a screening methacholine challenge each asthmatic had two ET-1 (doubling dose range, 0.96 to 15.36 nmol) and one methacholine (doubling dose range, 0.33 to 21.0 mumol) challenge, and normal subjects had a single ET-1 challenge. Inhalations were delivered using a dosimeter, and lung function measurements were made using constant-volume body plethysmography, with end points being a 35% fall in specific airway conductance (SGaw) and a 15% fall in FEV1. Samples for plasma ET-1 were taken before and after the inhalations, and pulse, blood pressure and oxygen saturation were monitored throughout the inhalations. All the asthmatic subjects displayed rapid-onset (< 5 min) dose-dependent bronchoconstriction to ET-1 across the dose range used, with mean (range) ET-1 PC35SGaw values of 5.15 (1.4 to 13.9) nmol, and 4.3 (1.2 to 8.3) nmol for the two ET-1 inhalations, and 0.42 (0.2 to 0.7) mumol for methacholine. Albuterol completely and rapidly reversed ET-1-induced bronchoconstriction, and in two patients not given albuterol, bronchoconstriction lasted 60 to 90 min. No significant bronchoconstriction was observed in any of the healthy volunteers across the ET-1 dose range used (mean PC35SGaw > 15.36 nmol). Oxygen saturation did not alter in either group, and plasma ET-1 did not change after ET-1 inhalation. Noninvasive blood pressure measurements revealed a fall in systolic blood pressure in normal subjects, with no change in asthmatics. Endothelin-1 is a potent bronchoconstrictor in asthma, with a bronchoconstrictor potency around 100 times that of methacholine in asthma. Asthmatics exhibit bronchial hyperreactivity to ET-1, and inhaled ET-1 can safely be given to asthmatics and normal subjects in the nebulized dose range 0.96 to 15.36 nmol.