α1-adrenoceptor subtypes mediating noradrenaline-induced contraction of pulmonary artery from pulmonary hypertensive rats

Vascular Reactions of the Diving Reflex in Men and Women Carrying Different ADRA1A Genotypes

The diving reflex is an oxygen-saving mechanism which is accompanied by apnea, reflex bradycardia development, peripheral vasoconstriction, spleen erythrocyte release, and selective redistribution of blood flow to the organs most vulnerable to lack of oxygen, such as the brain, heart, and lungs. However, this is a poorly studied form of hypoxia, with a knowledge gap on physiological and biochemical adaptation mechanisms. The reflective sympathetic constriction of the resistive vessels is realized via ADRA1A. It has been shown that ADRA1A SNP (p.Arg347Cys; rs1048101) is associated with changes in tonus in vessel walls. Moreover, the Cys347 allele has been shown to regulate systolic blood pressure. The aim of this work was to evaluate whether the ADRA1A polymorphism affected the pulmonary vascular reactions in men and women in response to the diving reflex. Men (n = 52) and women (n = 50) untrained in diving aged 18 to 25 were recruited into the study. The vascular reactions and blood flow were examined by integrated rheography and rheography of the pulmonary artery. Peripheral blood circulation was registered by plethysmography. The ADRA1A gene polymorphism (p.Arg347Cys; rs1048101) was determined by PCR-RFLP. In both men and women, reflective pulmonary vasodilation did occur in response to the diving reflex, but in women this vasodilation was more pronounced and was accompanied by a higher filling of the lungs with blood.. Additionally, ADRA1A SNP (p.Arg347Cys; rs1048101) is associated with sex. Interestingly, women with the Arg347 allele demonstrated the highest vasodilation of the lung vessels. Therefore, our data may help to indicate women with the most prominent adaptive reactions to the diving reflex. Our data also indicate that women and men with the Cys allele of the ADRA1A gene polymorphism have the highest risk of developing lung hypertension in response to the diving reflex. The diving reflex is an oxygen-saving mechanism which is accompanied by apnea, reflex bradycardia development, peripheral vasoconstriction, spleen erythrocyte release, and selective redistribution of blood flow to the organs most vulnerable to lack of oxygen, such as the brain, heart, and lungs. However, this is a poorly studied form of hypoxia, with a knowledge gap on physiological and biochemical adaptation mechanisms.

Long-Term High-Altitude Hypoxia and Alpha Adrenoceptor-Dependent Pulmonary Arterial Contractions in Fetal and Adult Sheep

Autonomic innervation of the pulmonary vasculature triggers vasomotor contractility predominately through activation of alpha-adrenergic receptors (α-ARs) in the fetal circulation. Long-term hypoxia (LTH) modulates pulmonary vasoconstriction potentially through upregulation of α₁-AR in the vasculature. Our study aimed to elucidate the role of α-AR in phenylephrine (PE)-induced pulmonary vascular contractility, comparing the effects of LTH in the fetal and adult periods on α-AR subtypes and PE-mediated Ca²⁺ responses and contractions. To address this, we performed wire myography, Ca²⁺ imaging, and mRNA analysis of pulmonary arteries from ewes and fetuses exposed to LTH or normoxia. Postnatal maturation depressed PE-mediated contractile responses. α₂-AR activation contracted fetal vessels; however, this was suppressed by LTH. α_1A- and α_1B-AR subtypes contributed to arterial contractions in all groups. The α_1D-AR was also important to contractility in fetal normoxic vessels and LTH mitigated its function. Postnatal maturity increased the number of myocytes with PE-triggered Ca²⁺ responses while LTH decreased the percentage of fetal myocytes reacting to PE. The difference between myocyte Ca²⁺ responsiveness and vessel contractility suggests that fetal arteries are sensitized to changes in Ca²⁺. The results illustrate that α-adrenergic signaling and vascular function change during development and that LTH modifies adrenergic signaling. These changes may represent components in the etiology of pulmonary vascular disease and foretell the therapeutic potential of adrenergic receptor antagonists in the treatment of pulmonary hypertension.

Suppressed baroreflex peripheral arc overwhelms augmented neural arc and incapacitates baroreflex function in rats with pulmonary arterial hypertension

NEW FINDINGS

What is the central question of this study? The impact of pulmonary arterial hypertension on open-loop baroreflex function, which determines how powerfully and rapidly the baroreflex operates to regulate arterial pressure, remains poorly understood. What is the main finding and its importance? The gain of the baroreflex total arc, indicating the baroreflex pressure-stabilizing function, is markedly attenuated in rats with monocrotaline-induced pulmonary arterial hypertension. This is caused by a rightward shift of the baroreflex neural arc and a downward shift of the peripheral arc. These findings contribute greatly to our understanding of arterial pressure regulation by the sympathetic nervous system in pulmonary arterial hypertension.

ABSTRACT

Sympathoexcitation has been documented in patients with established pulmonary arterial hypertension (PAH). Although the arterial baroreflex is the main negative feedback regulator of sympathetic nerve activity (SNA), the way in which PAH impacts baroreflex function remains poorly understood. In this study, we conducted baroreflex open-loop analysis in a rat model of PAH. Sprague-Dawley rats were injected with monocrotaline (MCT) s.c. to induce PAH (60 mg kg^-1 ; n = 11) or saline as a control group (CTL; n = 8). At 3.5 weeks after MCT injection, bilateral carotid sinuses were isolated, and intrasinus pressure (CSP) was controlled while SNA at the coeliac ganglia and arterial pressure (AP) were recorded. To examine the static baroreflex function, CSP was increased stepwise while steady-state AP (total arc) and SNA (neural arc) responses to CSP and the AP response to SNA (peripheral arc) were measured. Monocrotaline significantly decreased the static gain of the baroreflex total arc at the operating AP compared with CTL (-0.80 ± 0.31 versus -0.22 ± 0.22, P < 0.05). Given that MCT markedly increased plasma noradrenaline, an index of SNA, by approximately 3.6-fold compared with CTL, calibrating SNA by plasma noradrenaline revealed that MCT shifted the neural arc to a higher SNA level and shifted the peripheral arc downwards. Monocrotaline also decreased the dynamic gain of the baroreflex total arc (-0.79 ± 0.16 versus -0.35 ± 0.17, P < 0.05), while the corner frequencies that reflect the speed of the baroreflex remained unchanged (0.06 ± 0.02 versus 0.08 ± 0.02 Hz, n.s.). In rats with MCT-induced PAH, the suppressed baroreflex peripheral arc overwhelms the augmented neural arc and, in turn, attenuates the gain of the total arc, which determines the pressure-stabilizing capacity of the baroreflex.

[Adrenergic mechanisms of regulation of pulmonary microvessels tonicity and endothelial permeability]

The review contains the data on adrenergic mechanisms of regulation of pulmonary microvessels tonicity and endothelial permeability. On smooth muscle cells of pulmonary vessels there are postsynaptic α1A-, α1B-, α1D- and α2A-, α2B-, α2C-adrenoreceptors whose activation by norepinephrine induces vasoconstriction. Excitation of β1- and β2-subtypes of adrenoreceptors leads to vasodilatation, Activation of α1-2- and β1-3-adrenoreceptors of the endothelium contributes to enhancement of nitric oxide synthesis. The resulting reaction of pulmonary microvessels in response to administration of catecholamines appears be determined by interaction of adrenergic mechanisms of regulation of tonicity of smooth muscle cells and synthesis of nitric oxide by the endothelium. Constrictor and dilator reactions of pulmonary venous vessels in response to activation of α- and β-adrenoreceptors, respectively, are more pronounced than in pulmonary arteries and make a significant contribution to the shifts of pulmonary vascular resistance. Excitation of α2- and β2-adrenoreceptors of endothelial cells of microvessels of the lungs contributes to a decrease in their permeability. In order to find out the role of adrenergic mechanisms in shifts of the capillary filtration coefficient in simulating various pathology of pulmonary circulation, it is necessary to carry out integral studies that would make it possible to evaluate alterations in macro- and microhaemodynamics of the lungs.

Norepinephrine stimulation of alpha1D-adrenoceptor promotes proliferation of pulmonary artery smooth muscle cells via ERK-1/2 signaling

It has been shown that the sympathetic nervous system is activated in pulmonary arterial hypertension (PAH). Norepinephrine (NE) levels are increased by chemoreflex-dependent sympathetic overactivation and involved in pulmonary vascular remodeling. However, the underlying mechanisms of the remodeling induced by NE are poorly understood. In this study, we found that, in vivo, the expression of tyrosine hydroxylase and the concentration of plasma NE were increased in PAH rats compared with normal rats. Increases in ventricular hypertrophy and medial width of the pulmonary arteries were reversed by prazosin, α₁-adrenoceptor (α₁-AR) antagonists, in PAH rats. Elevated expression of α_1D-AR was detected in PAH rats. In addition, prazosin reduced the increasing expression of PCNA, CyclinA and CyclinE induced by hypoxia. In vitro, MTT assay, flow cytometry, Western blotting and immunofluorescence were performed to investigate the effects of NE on proliferation of pulmonary artery smooth muscle cells (PASMCs). We revealed that NE promoted PASMCs viability, increased the expression of PCNA, CyclinA and CyclinE, made more cells from G₀/G₁ phase to G₂/M+S phase and enhanced the microtubule formation. Above NE-induced changes could be suppressed by BMY 7378, an inhibitor of α_1D-AR. Furthermore, ERK-1/2 pathway was activated by NE. U0126, a specific inhibitor for ERK-1/2, attenuated the NE-induced proliferation of PASMCs under normoxia and hypoxia. Taken together, our results suggest that NE which stimulates α_1D-AR promotes proliferation of PASMCs and the effect is, at least in part, mediated via the ERK-1/2 pathway.

Perivascular adipose tissue, vascular reactivity and hypertension

Most blood vessels are surrounded by a variable amount of adventitial adipose tissue, perivascular adipose tissue (PVAT), which was originally thought to provide mechanical support for the vessel. It is now known that PVAT secretes a number of bioactive substances including vascular endothelial growth factor, tumor necrosis factor-alpha (TNF-α), leptin, adiponectin, insulin-like growth factor, interleukin-6, plasminogen activator substance, resistin and angiotensinogen. Several studies have shown that PVAT significantly modulated vascular smooth muscle contractions induced by a variety of agonists and electrical stimulation by releasing adipocyte-derived relaxing (ADRF) and contracting factors. The identity of ADRF is not yet known. However, several vasodilators have been suggested including adiponectin, angiotensin 1-7, hydrogen sulfide and methyl palmitate. The anticontractile effect of PVAT is mediated through the activation of potassium channels since it is abrogated by inhibiting potassium channels. Hypertension is characterized by a reduction in the size and amount of PVAT and this is associated with the attenuated anticontractile effect of PVAT in hypertension. However, since a reduction in size and amount of PVAT and the attenuated anticontractile effect of PVAT were already evident in prehypertensive rats with no evidence of impaired release of ADRF, there is the possibility that the anticontractile effect of PVAT was not directly related to an altered function of the adipocytes per se. Hypertension is characterized by low-grade inflammation and infiltration of macrophages. One of the adipokines secreted by macrophages is TNF-α. It has been shown that exogenously administered TNF-α enhanced agonist-induced contraction of a variety of vascular smooth muscle preparations and reduced endothelium-dependent relaxation. Other procontractile factors released by the PVAT include angiotensin II and superoxide. It is therefore possible that the loss could be due to an increased amount of these proinflammatory and procontractile factors. More studies are definitely required to confirm this.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Physiological significance of P2X receptor-mediated vasoconstriction in five different types of arteries in rats

P2X(1) receptors, the major subtype of P2X receptors in the vascular smooth muscle, are essential for α,β-methylene adenosine 5'-triphosphate (α,β-MeATP)-induced vasoconstriction. However, relative physiological significance of P2X(1) receptor-regulated vasoconstriction in the different types of arteries in the rat is not clear as compared with α(1)-adrenoceptor-regulated vasoconstriction. In the present study, we found that vasoconstrictive responses to noncumulative administration of α,β-MeATP in the rat isolated mesenteric arteries were significantly smaller than those to single concentration administration of α,β-MeATP. Therefore, we firstly reported the characteristic of α,β-MeATP-regulated vasoconstrictions in rat tail, internal carotid, pulmonary, mesenteric arteries, and aorta using single concentration administration of α,β-MeATP. The rank order of maximal vasoconstrictions for α,β-MeATP (E (max·α,β-MeATP)) was the same as that of maximal vasoconstrictions for noradrenaline (E (max·NA)) in the internal carotid, pulmonary, mesenteric arteries, and aorta. Moreover, the value of (E (max·α,β-MeATP)/E (max·KCl))/(E (max·NA)/E (max·KCl)) was 0.4 in each of the four arteries, but it was 0.8 in the tail artery. In conclusion, P2X(1) receptor-mediated vasoconstrictions are equally important in rat internal carotid, pulmonary, mesenteric arteries, and aorta, but much greater in the tail artery, suggesting its special role in physiological function.

Tension Measurement in Isolated Rat and Mouse Pulmonary Artery

Arterial vasoconstriction is an important physiological process in regulating blood pressure, and is involved in pathologies. The isolation of arteries from rats and mice, as well as the measurement of vascular tension in an ex vivo preparation, are important methods in studying the physiology of arteries and the pathophysiology associated with arterials. Three major methods to measure vascular tension are organ bath, wire myograph, and pressurized arterial myograph. The major method to measure vascular remodeling is by observing the zero-stress state of an artery.

Phenylephrine contracts porcine pulmonary veins via alpha(1B)-, alpha(1D)-, and alpha(2)-adrenoceptors

We have recently shown that the postjunctional alpha(2)-adrenoceptor mediating contraction of porcine pulmonary veins is of the alpha(2C)-subtype. We could also demonstrate that alpha(1)-adrenoceptors might contribute to the contraction in that blood vessel. In the present study, we aimed at characterising the alpha(1)-adrenoceptor subtype(s) involved using pharmacological and molecular biological methods. In isolated rings of porcine pulmonary veins the typical alpha(1)-adrenoceptor agonist phenylephrine caused a concentration-dependent contraction that was inhibited by the alpha(1B)-adrenoceptor selective antagonists 1-[4-(4-amino-6,7-dimethoxyquinazolin-2-yl)piperazin-1-yl]-2-[2-(isopropyl)-6-methoxyphenoxy]ethan-1-one (Rec15/2615; pA(2) 8.96+/-0.13) and 4-amino-2-[4-[1-(benzyloxycarbonyl)-2(S)-[[(1,1-dimethylethyl)amino]carbonyl]-piperazinyl]-6,7-dimethoxyquinazoline (L-765,314; pA(2) 7.22+/-0.05), as well as the alpha(1D)-adrenoceptor selective antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY7378; pA(2) 8.29+/-0.15, slope of the Schild plot 0.75+/-0.09, significantly different from unity, P<0.05), but not by the alpha(1A)-adrenoceptor selective antagonists (+/-)-1,3,5-trimethyl-6-[[3-[4-((2,3-dihydro-2-hydroxymethyl)-1,4-benzodioxin-5-yl)-1-piperazinyl]propyl]amino]-2,4(1H,3H)-pyrimidinedione (B8805-033) and N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alpha-dimethyl-1H-indole-3-ethanamine (RS-17053). These findings suggest that phenylephrine activates both alpha(1B)- and alpha(1D)-adrenoceptors. The observation was confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR) in porcine pulmonary veins, where mRNA signals for alpha(1B)- and alpha(1D)-adrenoceptors could be detected. However, the antagonist properties of rauwolscine and yohimbine (non-subtype selective alpha(2)-adrenoceptor antagonists) against phenylephrine showed that this agonist also activates alpha(2)-adrenoceptors in pulmonary veins. This was strengthened in experiments using tissues that were stimulated with forskolin (cell permeable activator of adenylyl cyclase). Phenylephrine mimicked the effect of the selective alpha(2)-adrenoceptor agonist UK14304 by causing an inhibition of forskolin-stimulated cAMP accumulation that was blocked by rauwolscine. It is concluded that, in addition to alpha(1B)- and alpha(1D)-adrenoceptors, phenylephrine can stimulate alpha(2)-adrenoceptors in porcine pulmonary veins.

α1-Adrenoceptor-dependent vascular hypertrophy and remodeling in murine hypoxic pulmonary hypertension

Excessive proliferation of vascular wall cells underlies the development of elevated vascular resistance in hypoxic pulmonary hypertension (PH), but the responsible mechanisms remain unclear. Growth-promoting effects of catecholamines may contribute. Hypoxemia causes sympathoexcitation, and prolonged stimulation of α1-adrenoceptors (α1-ARs) induces hypertrophy and hyperplasia of arterial smooth muscle cells and adventitial fibroblasts. Catecholamine trophic actions in arteries are enhanced when other conditions favoring growth or remodeling are present, e.g., injury or altered shear stress, in isolated pulmonary arteries from rats with hypoxic PH. The present study examined the hypothesis that catecholamines contribute to pulmonary vascular remodeling in vivo in hypoxic PH. Mice genetically deficient in norepinephrine and epinephrine production [dopamine β-hydroxylase−/− (DBH−/−)] or α1-ARs were examined for alterations in PH, cardiac hypertrophy, and vascular remodeling after 21 days exposure to normobaric 0.1 inspired oxygen fraction (FiO2). A decrease in the lumen area and an increase in the wall thickness of arteries were strongly inhibited in knockout mice (order of extent of inhibition: DBH−/− = α1D-AR−/− > α1B-AR−/−). Distal muscularization of small arterioles was also reduced (DBH−/− > α1D-AR−/− > α1B-AR−/− mice). Despite these reductions, increases in right ventricular pressure and hypertrophy were not attenuated in DBH−/− and α1B-AR−/− mice. However, hematocrit increased more in these mice, possibly as a consequence of impaired cardiovascular activation that occurs during reduction of FiO2. In contrast, in α1D-AR−/− mice, where hematocrit increased the same as in wild-type mice, right ventricular pressure was reduced. These data suggest that catecholamine stimulation of α1B- and α1D-ARs contributes significantly to vascular remodeling in hypoxic PH.

Enhanced α1-adrenergic trophic activity in pulmonary artery of hypoxic pulmonary hypertensive rats

Mechanisms that induce the excessive proliferation of vascular wall cells in hypoxic pulmonary hypertension (PH) are not fully understood. Alveolar hypoxia causes sympathoexcitation, and norepinephrine can stimulate α1-adrenoceptor (α1-AR)-dependent hypertrophy/hyperplasia of smooth muscle cells and adventitial fibroblasts. Adrenergic trophic activity is augmented in systemic arteries by injury and altered shear stress, which are key pathogenic stimuli in hypoxic PH, and contributes to neointimal formation and flow-mediated hypertrophic remodeling. Here we examined whether norepinephrine stimulates growth of the pulmonary artery (PA) and whether this is augmented in PH. PA from normoxic and hypoxic rats [9 days of 0.1 fraction of inspired O2 (FiO2)] was studied in organ culture, where wall tension, Po2, and Pco2 were maintained at values present in normal and hypoxic PH rats. Norepinephrine treatment for 72 h increased DNA and protein content modestly in normoxic PA (+10%, P < 0.05). In hypoxic PA, these effects were augmented threefold ( P < 0.05), and protein synthesis was increased 34-fold ( P < 0.05). Inferior thoracic vena cava from normoxic or hypoxic rats was unaffected. Norepinephrine-induced growth in hypoxic PA was dose dependent, had efficacy greater than or equal to endothelin-1, required the presence of wall tension, and was inhibited by α1A-AR antagonist. In hypoxic pulmonary vasculature, α1A-AR was downregulated the least among α1-AR subtypes. These data demonstrate that norepinephrine has trophic activity in the PA that is augmented by PH. If evident in vivo in the pulmonary vasculature, adrenergic-induced growth may contribute to the vascular hyperplasia that participates in hypoxic PH.

Attenuated Noradrenaline-Induced Contraction of Pulmonary Arteries from Rats Treated with Monocrotaline: Role of Rho Kinase

Noradrenaline-induced pulmonary artery contraction was reduced in monocrotaline-treated rats. The possibility that this could be due to alterations in the rho kinase pathway was examined in this study. A combination of nifedipine (10(-6) M) and thapsigargin (10(-6) M) attenuated noradrenaline-induced contraction significantly more in artery segments from monocrotaline-treated rats than in artery segments from control rats indicating a reduced role for calcium sensitization in artery segments from monocrotaline-treated rats. In artery segments permeabilized with ionomycin, CaCl(2) (1.25 mmol/l) produced significantly greater contraction in monocrotaline treated rats compared with control rats. Addition of noradrenaline (10(-5) M) to the bath produced further contractions in both groups. However, noradrenaline-induced contraction was less in monocrotaline-treated rats compared with controls. Y-27632 concentration dependently relaxed ring segments of pulmonary artery pre-contracted with noradrenaline (10(-5)M). The pIC(50) values were 6.46+/- 0.09 (n=5) 5.81+/- 0.06 (n=5) in control and pulmonary hypertensive rings, respectively. The maximum relaxation to Y-27632 was significantly higher in monocrotaline-treated rats. ROCK II was the predominant isoform of rho kinase expressed in the pulmonary artery. The level of expression was increased in rats treated with monocrotaline. These results would suggest that while basal rho kinase activity was elevated in monocrotaline-induced pulmonary hypertension, noradrenaline-induced contraction was attenuated, suggesting poor coupling of the receptor activation to rho kinase activation.

Effects of norepinephrine on α-subtype receptors in the feline pulmonary vascular bed

OBJECTIVE

To test the hypothesis that norepinephrine induces a pressor response in the pulmonary vascular bed of the cat and identify the alpha-(1)adrenoceptor subtypes involved in the mediation or modulation of these effects.

DESIGN

Prospective vehicle controlled study.

SETTING

University research laboratory.

SUBJECTS

Intact chest preparation, adult mongrel cats.

INTERVENTIONS

In separate experiments, the effects of 5-methyl-urapidil, a selective alpha-(1)A-subtype adrenoceptor antagonist, chloroethylclonidine, an alpha-(1)B-subtype and -(1)D-subtype adrenoceptor antagonist, and BMY 7378, the selective alpha-(1)D-subtype adrenoceptor antagonist, were investigated on pulmonary arterial responses to norepinephrine and other agonists in the pulmonary vascular bed of the cat.

MEASUREMENTS AND MAIN RESULTS

The systemic pressure and lobar arterial perfusion pressure were continuously monitored, electronically averaged, and permanently recorded. In the feline pulmonary vascular bed of the isolated left lower lobe, norepinephrine induced a dose-dependent vasoconstrictor response that was not significantly altered after administration of BMY 7378. However, the responses to norepinephrine were significantly attenuated following administration of 5-methyl-urapidil and chloroethylclonidine.

CONCLUSIONS

The results of the present study suggest that norepinephrine has potent vasopressor activity in the pulmonary vascular bed of the cat and that this response may be mediated or modulated by both alpha-(1)A-subtype and -(1)B-subtype adrenoceptor sensitive pathways.