Effects of propranolol and L-NAME on beta-adrenoceptor-mediated relaxation in rat carotid artery

Antagonism of α1-adrenoceptors by β3-adrenergic agonists: Structure-function relations of different agonists in prostate smooth muscle contraction

Effects of β₃-adrenergic agonists on prostate smooth muscle contraction are poorly characterized, although mirabegron is used for treatment of lower urinary tract symptoms. Off-target effects of several β₃-adrenergic agonists include antagonism of α₁-adrenoceptors. Proposed, but unconfirmed explanations include phenylethanolamine backbones, found in some β₃-adrenergic agonists and imparting interaction with catecholamine binding pockets of adrenoceptors. Here, we examined effects of β₃-adrenergic agonists on contractions of human prostate tissues, including ZD7114 (without phenylethanolamine moiety), ZD2079 (phenylethanolamine backbone), BRL37344 and CL316243 (chloride-substituted phenylethanolamine deriatives). Prostate tissues were obtained from radical prostatectomy. Contractions by α₁-adrenergic agonists and electric field stimulation (EFS) were studied in an organ bath. ZD7114 (10 µM) right-shifted concentration responses curves for α₁-adrenergic agonists, resulting in increased EC₅₀ values for phenylephrine, methoxamine and noradrenaline up to one magnitude, without affecting E_max values. ZD7114 (10 µM) inhibited EFS-induced contractions, resulting in reduced E_max values. All effects of ZD7114 were resistant to the β₃-adrenergic antagonist L-748337, including increases in EC₅₀ values for α₁-adrenergic agonists, up to more than two magnitudes. Using 10 µM, neither ZD2079, BRL37344 or CL316243 affected α₁-adrenergic or EFS-induced contractions. At escalated concentrations, BRL37344 (200 µM) right-shifted concentration response curves for phenylephrine, increased EC₅₀ values for phenylephrine, and inhibited EFS-induced contractions, while CL316243 (300 µM) did not affect phenylephrine- or EFS-induced contractions. In conclusion, phenylethanolamine backbones are not decisive to impart α₁-adrenoceptor antagonism to β₃-agonists. Effects of β₃-adrenergic agonists on prostate smooth muscle contraction are limited to off-target effects, including α₁-adrenoceptor antagonism by ZD7114 and BRL37344.

Emerging Roles of Sympathetic Nerves and Inflammation in Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) is no longer recognised as simply a structural support for the vasculature, and we now know that PVAT releases vasoactive factors which modulate vascular function. Since the discovery of this function in 1991, PVAT research is rapidly growing and the importance of PVAT function in disease is becoming increasingly clear. Obesity is associated with a plethora of vascular conditions; therefore, the study of adipocytes and their effects on the vasculature is vital. PVAT contains an adrenergic system including nerves, adrenoceptors and transporters. In obesity, the autonomic nervous system is dysfunctional; therefore, sympathetic innervation of PVAT may be the key mechanistic link between increased adiposity and vascular disease. In addition, not all obese people develop vascular disease, but a common feature amongst those that do appears to be the inflammatory cell population in PVAT. This review will discuss what is known about sympathetic innervation of PVAT, and the links between nerve activation and inflammation in obesity. In addition, we will examine the therapeutic potential of exercise in sympathetic stimulation of adipose tissue.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

Beta2-adrenergic activity modulates vascular tone regulation in lecithin:cholesterol acyltransferase knockout mice

Lecithin:cholesterol acyltransferase (LCAT) deficiency is associated with hypoalphalipoproteinemia, generally a predisposing factor for premature coronary heart disease. The evidence of accelerated atherosclerosis in LCAT-deficient subjects is however controversial. In this study, the effect of LCAT deficiency on vascular tone and endothelial function was investigated in LCAT knockout mice, which reproduce the human lipoprotein phenotype. Aortas from wild-type (Lcat^wt) and LCAT knockout (Lcat^KO) mice exposed to noradrenaline showed reduced contractility in Lcat^KO mice (P < 0.005), whereas acetylcholine exposure showed a lower NO-dependent relaxation in Lcat^KO mice (P < 0.05). Quantitative PCR and Western blotting analyses suggested an adequate eNOS expression in Lcat^KO mouse aortas. Real-time PCR analysis indicated increased expression of β2-adrenergic receptors vs wild-type mice. Aorta stimulation with noradrenaline in the presence of propranolol, to abolish the β-mediated relaxation, showed the same contractile response in the two mouse lines. Furthermore, propranolol pretreatment of mouse aortas exposed to L-NAME prevented the difference in responses between Lcat^wt and Lcat^KO mice. The results indicate that LCAT deficiency leads to increased β2-adrenergic relaxation and to a consequently decreased NO-mediated vasodilation that can be reversed to guarantee a correct vascular tone. The present study suggests that LCAT deficiency is not associated with an impaired vascular reactivity.

Lack of β2 -adrenoceptors aggravates heart failure-induced skeletal muscle myopathy in mice

Skeletal myopathy is a hallmark of heart failure (HF) and has been associated with a poor prognosis. HF and other chronic degenerative diseases share a common feature of a stressed system: sympathetic hyperactivity. Although beneficial acutely, chronic sympathetic hyperactivity is one of the main triggers of skeletal myopathy in HF. Considering that β2 -adrenoceptors mediate the activity of sympathetic nervous system in skeletal muscle, we presently evaluated the contribution of β2 -adrenoceptors for the morphofunctional alterations in skeletal muscle and also for exercise intolerance induced by HF. Male WT and β2 -adrenoceptor knockout mice on a FVB genetic background (β2 KO) were submitted to myocardial infarction (MI) or SHAM surgery. Ninety days after MI both WT and β2 KO mice presented to cardiac dysfunction and remodelling accompanied by significantly increased norepinephrine and epinephrine plasma levels, exercise intolerance, changes towards more glycolytic fibres and vascular rarefaction in plantaris muscle. However, β2 KO MI mice displayed more pronounced exercise intolerance and skeletal myopathy when compared to WT MI mice. Skeletal muscle atrophy of infarcted β2 KO mice was paralleled by reduced levels of phosphorylated Akt at Ser 473 while increased levels of proteins related with the ubiquitin--proteasome system, and increased 26S proteasome activity. Taken together, our results suggest that lack of β2 -adrenoceptors worsen and/or anticipate the skeletal myopathy observed in HF.

Vasodilatory mechanisms of beta receptor blockade

Beta-blockers are widely prescribed for the treatment of a variety of cardiovascular pathologies. Compared to traditional beta-adrenergic antagonists, beta-blockers of the new generation exhibit ancillary properties such as vasodilation through different mechanisms. This translates into a more favorable hemodynamic profile. The relative affinities of beta-adrenoreceptor antagonists towards the three beta-adrenoreceptor isotypes matter for predicting their functional impact on vasomotor control. This review will focus on the mechanisms underlying beta-blocker-evoked vasorelaxation with a specific emphasis on agonist properties of beta(3)-adrenergic receptors.

β(3) Receptors: Role in Cardiometabolic Disorders

Pharmacological and molecular approaches have shown that an atypical β-adrenoceptor (AR), called β(3)-AR, that is distinct from β(1)-ARs and β(2)-ARs, exists in some tissues in heterogeneous populations such as β(3a)-ARs and β(3b)-ARs. β(3)-ARs belong to a superfamily of receptors linked to guanine nucleotide binding proteins (G proteins). The β(3)-AR gene contains two introns whereas the β(1)-AR and β(2)-AR genes are intronless, leading to splice variants. β(3)-ARs can couple to G(i) and G(s) and they are reported to be present in brown adipose tissue, vasculature, the heart, among other tissues. β(3)-ARs cause vasodilation of microvessels in the islets of Langerhans and may participate in the pathogenesis of cardiac failure, during which modification of β(1)-AR and β(2)-AR expression occurs. The development of β(3)-AR agonists has led to the elaboration of promising new drugs, including antiobesity and antidiabetic drugs. This article reviews the various pharmacological actions of β(3)-ARs and their clinical implications for diabetes and cardiovascular diseases.

Age-related changes in the sympathetic innervation of cerebral vessels and in carotid vascular responses to norepinephrine in the rat: in vitro and in vivo studies

We hypothesized that the density of sympathetic noradrenergic innervation of cerebral arteries and vasoconstrictor responses evoked in carotid circulation by norepinephrine (NE) increase with maturation and age. In rats of 4-5, 10-12, and 42-44 wk of age (juvenile, mature, middle aged), glyoxylic acid applied to stretch preparations showed the density of noradrenergic nerves in basilar and middle cerebral arteries was greater in mature than juvenile or middle-aged rats. In anesthetized rats, infusion of NE (2.5 mug/kg iv) increased mean arterial pressure (ABP) to approximately 180 mmHg in mature and middle-aged but to only approximately 150 mmHg in juveniles rats. Concomitantly, carotid blood flow (CBF) decreased in mature and middle-aged rats but remained constant in juveniles because carotid vascular conductance (CVC) decreased more in mature and middle-aged than juvenile rats. We also hypothesized that nitric oxide (NO) blunts cerebral vasoconstrictor responses to NE. Inhibition of NO synthase with l-NAME (10 mg/kg iv) induced similar increases in baseline ABP in each group, but larger decreases in CVC and CBF in mature and middle-aged than juvenile rats. Thereafter, the NE-evoked increase in ABP was similar in juvenile and mature but accentuated in middle-aged rats. Concomitantly, NE decreased CVC in juvenile and mature, but not middle-aged rats; in them, CBF increased. Thus, in juvenile rats, sparse noradrenergic innervation of cerebral arteries is associated with weak NE-evoked pressor responses and weak carotid vasoconstriction that allows autoregulation of CBF. Cerebral artery innervation density increases with maturation but lessens by middle age. Meanwhile, NE-evoked pressor responses and carotid vasoconstriction are stronger in mature and middle-aged rats, such that CBF falls despite the evoked increase in ABP. We propose that in juvenile and mature rats, NO does not modulate NE-evoked pressor responses, cerebral vasoconstriction, or CBF autoregulation, but by middle age, NO limits pressor responses and prevents breakthrough of CBF in the upper part of the autoregulatory range.

Beta3-adrenergic receptors in cardiac and vascular tissues emerging concepts and therapeutic perspectives

Catecholamines released by the orthosympathetic system play a major role in the short- and long-term regulation of cardiovascular function. Beta1- and beta2-adrenoreceptors (ARs) have classically been considered as mediating most of their effects on cardiac contraction. After their initial cloning and pharmacologic characterization in the late 1980s, beta3-ARs have been mostly thought of as receptors mediating metabolic effects (e.g., lipolysis) in adipocytes. However, definitive evidence for their expression and functional coupling in cardiovascular tissues (including in humans) has recently initiated a re-examination of their implication in the pathophysiology of cardiovascular diseases. Distinctive pharmacodynamic properties of beta3-AR, e.g., their upregulation in disease and resistance to desensitization, suggest that they may be attractive targets for therapeutic intervention. They may substitute efficient vasodilating pathways when beta1/2-ARs are inoperative. In the heart, their contractile effects, which are functionally antipathetic to those of beta1/2-AR, may protect the myocardium against adverse effects of excessive catecholamine stimulation and perhaps mediate additional ancillary effects on key aspects of electrophysiology or remodeling. Longitudinal studies in animals and patients with different stages of heart failure are now needed to identify the optimal therapeutic scheme using specific combinations of agonists or antagonists at all three beta-ARs.

Effects of chronic nitric oxide synthase inhibition on the cardiovascular responses to cannabinoids in vivo and in vitro

BACKGROUND AND PURPOSE

Since the vasorelaxant potency of the endocannabinoid anandamide is enhanced in perfused mesenteric vascular beds from rats made hypertensive by chronic inhibition of NO synthase (L-NAME in drinking water), we hypothesized that in vivo, anandamide-induced vasodilatation would be similarly enhanced in L-NAME-treated animals.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were given L-NAME in drinking water (7.5 mg kg(-1) day(-1)) for 4 weeks. Relaxant effects of anandamide were measured in perfused mesenteric vascular beds and in isolated small mesenteric arteries. Renal, mesenteric and hindquarters haemodynamic responses to anandamide, methanandamide, the synthetic cannabinoid agonist WIN-55212-2 and the cannabinoid receptor antagonist AM251 were assessed in conscious, chronically-instrumented rats.

KEY RESULTS

Vasorelaxant responses to anandamide were enhanced in the perfused mesentery but not in isolated mesenteric resistance vessels. In vivo, anandamide caused vasodilatation only in the hindquarters vascular bed and only in control rats. Methanandamide caused a late-onset (40 min after administration) tachycardia, mesenteric and hindquarters vasoconstriction, and renal vasodilatation, which did not differ between control and L-NAME-treated rats. AM251 had no effect on resting blood pressure in control or L-NAME-treated rats and WIN55212-2 caused pressor and renal and mesenteric vasoconstrictor responses, with hindquarters vasodilatation in both groups of animals.

CONCLUSIONS AND IMPLICATIONS

The results provide no in vivo evidence for enhanced vasodilator responses to cannabinoids, or up-regulation of endocannabinoids or their receptor activity, following chronic NO synthase inhibition.

Role of NO in the systemic hemodynamic response to β2-adrenoceptor stimulation

Blockade of NO synthesis in most narcotized rats was followed by an increase in depressor effects (by 45%) and decrease in total peripheral resistance (by 63%) upon treatment with isopropyl norepinephrine (isoproterenol). Our results indicate that NO secretion in the endothelium modulates the systemic hemodynamic response to beta(2)-adrenoceptor stimulation.

Direct demonstration of beta1- and evidence against beta2- and beta3-adrenoceptors, in smooth muscle cells of rat small mesenteric arteries

1 Recent evidence supports additional subtypes of vasodilator beta-adrenoceptor (beta-AR) besides the 'classical' beta(2). The aim of this study was to investigate the distribution of beta-ARs in the wall of rat mesenteric resistance artery (MRA), to establish the relative roles of beta-ARs in smooth muscle and other cell types in mediating vasodilatation and to analyse this in relation to the functional pharmacology. 2 We first examined the vasodilator beta-AR subtype using 'subtype-selective' agonists against the, commonly employed, phenylephrine-induced tone. Concentration-related relaxation was produced by isoprenaline (pEC(50): 7.70+/-0.1) (beta(1) and beta(2)). Salbutamol (beta(2)), BRL 37344 (beta(3)) and CGP 12177 (atypical beta) caused relaxation but were 144, 100 and 263 times less potent than isoprenaline; the 'beta(3)-adrenoceptor agonist' CL 316243 was ineffective. 3 In arteries precontracted with 5-HT or U 46619, isoprenaline produced concentration-related relaxation but salbutamol, BRL 37344, CGP 12177 and CL 316243 did not. SR 59230A, CGP 12177 and BRL 37344 caused a parallel rightward shift in the concentration-response curve to phenylephrine indicating competitive alpha(1)-AR antagonism, explaining the false-positive 'vasodilator' action against phenylephrine-induced tone. Endothelial denudation but not L-NAME slightly attenuated isoprenaline-mediated vasodilatation in phenylephrine and U 46619 precontracted MRA. 4 The beta-AR fluorescent ligand BODIPY TMR-CGP 12177 behaved as an irreversible beta(1)-AR antagonist in MRA and bound to the surface and inside vascular smooth muscle cells in intact vascular wall. Beta-ARs in smooth muscle cells were observed in a perinuclear location, consistent with the location of Golgi and endoplasmic reticulum. 5 Binding of BODIPY TMR-CGP 12177 was inhibited by BAAM (1 microM) in all three vascular tunics, confirming the presence of beta-ARs in adventitia, media and intima. Binding in adventitia was observed in both neuronal and non-neuronal cell types. Lack of co-localisation with a fluorescent ligand for alpha-ARs confirms the selectivity of BODIPY TMR-CGP 12177 for beta-ARs over alpha-ARs. 6 Our results support the presence of functional vasodilator beta(1)-ARs and show that they are mainly located in smooth muscle cells. Furthermore, we have demonstrated, for the first time, the usefulness of BODIPY TMR-CGP 12177 for identifying beta-AR distribution in the 'living' vascular wall.

Role of β2-adrenoceptors (ß-AR), but not ß1-, β3-AR and endothelial nitric oxide, in β-AR-mediated relaxation of rat intrapulmonary artery

The aim of this study was to analyze beta-adrenoceptor (beta-AR)-mediated relaxation in rat intralobar pulmonary artery. The relaxant responses of beta-AR agonists were characterized using beta-AR antagonists in prostaglandin F2alpha (PGF2alpha)-precontracted arteries. The role of nitric oxide (NO) and endothelium in beta-AR-mediated relaxation was also investigated. Isoprenaline (a non-selective beta-AR agonist) and salbutamol (a selective beta2-AR agonist) induced vasorelaxation. ICI 118551 (a selective beta2-AR antagonist) antagonized the effect of both isoprenaline and salbutamol (pA2 values of 9.57 and 9.51 respectively). In contrast, atenolol (1 microM) and CGP 20712A (0.1 microM), two beta1-AR antagonists, did not modify the relaxing effect of isoprenaline. The response to isoprenaline obtained in the presence of nadolol (10 microM, a beta1/beta2-AR antagonist) was not further inhibited by SR 59230A (1 microM, a selective beta3-AR antagonist). The non-beta1/beta2-AR agonists studied (BRL 37344, SR 58611A, and CGP 12177A) did not elicit vasorelaxation. Relaxation to isoprenaline and salbutamol was unaffected by L-N(G)-nitro-arginine methyl ester (100 microM, an inhibitor of NO synthase) or after endothelium removal. These results demonstrate the role of beta2-AR in mediating relaxation in rat intralobar pulmonary artery precontracted with PGF2alpha. They indicate that beta2-AR-mediated relaxation in this artery is NO- and endothelium-independent. Furthermore, they do not provide evidence of a relaxant role of either beta1- or beta3-AR in PGF2alpha-precontracted rat intrapulmonary artery.

Comparison of the alpha-adrenoceptor-mediated effects of beta3-adrenoceptor ligands in rat pulmonary artery

We have recently shown that the beta-adrenoceptor ligands CGP 12177, bupranolol, and SR 59230A (aryloxypropanolamines), but not BRL 37344 and CL 316243 (phenylethanolamines), exhibit significant affinity for alpha1-adrenoceptors and that CGP 12177 displays partial agonist properties at alpha-adrenoceptors in rat pulmonary artery. In this study, bupranolol and SR 59230A were further evaluated for their potential alpha-adrenoceptor mediated effects (i.e., agonist and/or antagonist properties) in rat intralobar pulmonary artery and compared with BRL 37344 and CL 316243. Bupranolol induced a relaxation in phenylephrine-precontracted arteries, but had no effect in prostaglandin F2alpha(PGF2alpha) -precontracted ones. SR 59230A also elicited a relaxation in phenylephrine-precontracted arteries. In PGF2alpha -precontracted arteries, SR 59230A induced a contractile response that was insensitive to the irreversible alpha-adrenoceptor antagonist phenoxybenzamine. BRL 37344 at high concentrations, but not CL 316243, produced slight relaxation in both phenylephrine- and PGF2alpha -precontracted arteries. The contractile response to phenylephrine was antagonized by bupranolol and SR 59230A in a competitive manner (pA2: 6.38 and 7.08 respectively). The concentration-response curve to phenylephrine was also shifted to the right by BRL 37344 (mean pKb: 4.45), but not by CL 316243 (100 microM). This study indicates that the aryloxypropanolamine derivatives bupranolol and SR 59230A exhibit competitive antagonist, but no agonist properties on alpha1-adrenoceptors, SR 59230A also inducing alpha-adrenoceptor-independent contraction. Among the phenylethanolamines, BRL 37344 but not CL 316243, also exerts an antagonist effect on alpha1-adrenoceptors, with a much lower potency than the aryloxypropanolamines studied.

Ligands at β2-, β3-, and the Low-Affinity State of β1-Adrenoceptors Block the α1-Adrenoceptor-Mediated Constriction in Human Pulmonary and Rat Mesenteric Arteries

We examined whether the beta2-adrenoceptor agonists fenoterol and salbutamol, the beta3-adrenoceptor agonists CL 316243 and ZD 2079, and the agonists of the low-affinity state of beta-adrenoceptors, cyanopindolol and CGP 12177 block alpha1-adrenoceptors in that concentration range in which they relax the human pulmonary and rat mesenteric arteries preconstricted with phenylephrine 10 microM and 1 microM, respectively. For quantification of vasodilatation pEC25 values and for the antagonism toward alpha1-adrenoceptors, pA2 values were determined. We found that in the rat mesenteric artery, (1) the pEC25 values of the beta-adrenoceptor ligands resemble their respective pA2 values (difference < or = 0.9 log units), and (2) the order of potencies is the same for both parameters, ie, cyanopindolol approximately fenoterol > CGP 12177 > salbutamol > ZD 2079 > CL 316243. In the human pulmonary artery, (1) the pEC25 values are slightly lower (by 0.6-1.3 log units) than their respective pA2 values, and (2) the rank order of potencies is the same for both parameters. In conclusion, the present study suggests that ligands of beta2-adrenoceptors and of non-beta1-non-beta2-adrenoceptors relax rat and human vessels preconstricted with phenylephrine or norepinephrine mainly through their alpha1-adrenolytic effects. Hence, for the investigation of the role of beta-adrenoceptors in vessels, the constrictor agent should be chosen with great caution.

Impairment of the low-affinity state beta1-adrenoceptor-induced relaxation in spontaneously hypertensive rats

1 In hypertension, a decrease of the vascular beta-adrenergic relaxation has been described. However, the specific involvement of each beta-adrenoceptor (beta-AR) subtype, in particular the low-affinity state of beta1-AR, has not yet been evaluated. We investigated whether the low-affinity state of beta1-AR-induced relaxation was impaired in Spontaneously Hypertensive Rats (SHR). 2 The relaxant responses to CGP 12177 and cyanopindolol, low-affinity state beta1-AR agonists (with beta1-/beta2-AR antagonistic and partial beta3-AR agonistic properties) were evaluated on thoracic aortic rings isolated from 12-weeks-old Wistar Kyoto rats (WKY) and SHR. 3 In WKY, CGP 12177 and cyanopindolol produced an endothelium and nitric oxide (NO)-independent relaxation. CGP 12177-induced endothelium-independent relaxation was not modified either by beta1-, beta2-AR (nadolol) or beta3-AR (L-748337 or SR 59230A) antagonists but was significantly reduced by high concentrations of CGP 20712A (P<0.05). This relaxation was also reduced by adenylyl cyclase inhibitors, SQ 22536 or MDL 12330A. 4 In SHR, CGP 12177 produced mainly an endothelium and NO-dependent relaxation. This effect was not modified by nadolol, but was strongly reduced by beta3-AR blockade. Endothelium-independent relaxation to CGP 12177 was not altered by adenylyl cyclase inhibition, but was amplified in preparations from pertussis toxin-pretreated SHR. 5 The immunohistochemical analysis revealed an upregulation of beta3-AR in the endothelial layer of SHR aorta, whereas the beta3-AR-induced relaxation was not modified. 6 In conclusion, we demonstrated an impaired low-affinity state of the beta1-AR-induced relaxation and an upregulation of the beta3-AR in hypertension. Some clinical implications of those findings are discussed.

Endothelin-1 limits vascular smooth muscle beta-adrenergic receptor sensitivity by a PKC-dependent pathway

Endothelin-1 reduces the chronotropic and inotropic effects of the beta-adrenoceptor agonist isoproterenol in rabbit isolated atria. Vascular interactions between endothelin-1 and isoproterenol have not been reported. Rings of the rabbit aorta without endothelium were mounted on myographs to measure isometric tension. Vessels were precontracted to similar levels with phenylephrine (30 micromol/L) or endothelin-1 (30 nmol/L). Relaxation to isoproterenol and forskolin were obtained. Vascular sensitivity (pD2) to isoproterenol was not different in the presence of endothelin-1 (7.6 +/- 0.3; n = 13) and phenylephrine (7.5 +/- 0.3; n = 11). The maximal relaxation (Emax) however, was doubled (P < 0.05) by endothelin-1 (42 +/- 5%), as compared with phenylephrine (23 +/- 4%). In the presence of endothelin-1, chelerythrine (protein kinase C inhibitor; 10 micromol/L) increased (P < 0.05) vascular sensitivity to isoproterenol (8.6 +/- 0.4, n = 7), but had no influence on the Emax. In contrast, in the presence of phenylephrine, pD2 was unaffected by chelerythrine, whereas the Emax to isoproterenol was increased (P < 0.05; 50 +/- 4%, n = 8). Vascular sensitivity and Emax to forskolin were similar in the presence of endothelin-1 and phenylephrine. In conclusion, endothelin-1 reduces vascular sensitivity to isoproterenol in a PKC-dependent pathway. The permissive effect of endothelin-1 appears to directly target the beta-adrenoceptor/G protein complex upstream of adenylate cyclase.

Role of alpha-adrenergic receptors in the effect of the beta-adrenergic receptor ligands, CGP 12177, bupranolol, and SR 59230A, on the contraction of rat intrapulmonary artery

This study investigates the effect of the aryloxypropanolamines 4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one (CGP 12177), bupranolol, and 3-(2-ethylphenoxy)-1[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol oxalate (SR 59230A) [commonly used as beta(3)- and/or atypical beta-adrenergic receptors (beta-AR) ligands] on the contractile function of rat intralobar pulmonary artery. Affinities of beta-AR ligands for alpha(1)-adrenergic receptors (alpha(1)-AR) were also evaluated using [(3)H]prazosin binding competition experiments performed in rat cortical membranes. In intralobar pulmonary artery, CGP 12177 did not modify the basal tone, but antagonized the contraction induced by the alpha(1)-AR agonist phenylephrine (PHE). In arteries precontracted with PHE, CGP 12177 elicited relaxation, whereas in those precontracted with prostaglandin F(2alpha) (PGF(2alpha)), it further enhanced contraction. CGP 12177 induced an increase in intracellular calcium concentration in pressurized arteries loaded with Fura PE-3 and precontracted with PGF(2alpha). In PGF(2alpha) precontracted arteries, phentolamine (an alpha-AR antagonist) and phenoxybenzamine (an irreversible alpha-AR antagonist) antagonized the contractile responses to PHE and CGP 12177. Both responses were also decreased by bupranolol and SR 59230A. Specific [(3)H]prazosin binding was displaced by CGP 12177, bupranolol, and SR 59230A with pK(i) values of 5.2, 5.7, and 6.6, respectively. In contrast, (+/-)-(R*,R*)-[4-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]phenoxy]acetic acid sodium (BRL 37344) and disodium 5-[(2R)-2-([(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL 316243) (nonaryloxypropanolamines beta(3)-AR agonists) displayed very low affinity for [(3)H]prazosin binding sites (pK(i) values below 4). These data suggest that CGP 12177 exhibits partial agonist properties for alpha(1)-AR in rat pulmonary artery. They also show that bupranolol and SR 59230A exert an alpha(1)-AR antagonist effect. As a consequence, these aryloxypropanolamine compounds should be used with caution when investigating the role of beta(3)- and atypical beta-AR in the regulation of vascular tone.

Atypical beta-adrenoceptors, different from beta 3-adrenoceptors and probably from the low-affinity state of beta 1-adrenoceptors, relax the rat isolated mesenteric artery

(1) We examined whether beta3- and/or atypical beta-adrenoceptors relax the rat isolated mesenteric artery. (2) Mesenteric arteries precontracted with phenylephrine were relaxed by beta-agonists with the following potencies (pD2): nonselective agonist isoprenaline (6.00)>nonconventional partial agonist cyanopindolol (5.45)>beta2-agonist fenoterol (4.98)>nonconventional partial agonist CGP 12177 (4.19)>beta3-agonist ZD 2079 (3.72). The beta3-agonist CL 316243 1 mm relaxed the vessel only marginally. (3) The concentration-response curves (CRCs) for cyanopindolol, CGP 12177 and ZD 2079 were not affected by the nonselective beta-antagonist propranolol 0.3 microm, the beta2-antagonist ICI 118551 1 microm and by CL 316243 60 microm, but shifted to the right by bupranolol (pA2 5.3-5.7), CGP 20712 (5.4) and SR 59230A (6.5-6.7) (the latter three drugs block atypical and/or beta3-adrenoceptors at high concentrations). (4) The CRC for isoprenaline was shifted to the right by propranolol (pA2 7.0) but, in the presence of propranolol 0.3 microm, not affected by SR 59230A 1 microm. The CRC for fenoterol was shifted to the right by propranolol (pA2 6.9) and ICI 118551 (6.8). (5) Removal of endothelium diminished the vasorelaxant effects of cyanopindolol, CGP 12177 and ZD 2079. (6) Fenoterol and cyanopindolol also relaxed (endothelium-intact) mesenteric arteries precontracted with serotonin. The relaxant effect of cyanopindolol was antagonized by bupranolol to about the same degree as in phenylephrine-contracted vessels. (7) In conclusion, beta2- and atypical beta-adrenoceptors (but not beta3-adrenoceptors) relax the rat mesenteric artery. The atypical beta-adrenoceptor, which is partially located endothelially, may differ from the low-affinity state of the beta1-adrenoceptor.

Effects of two beta3-agonists, CGP 12177A and BRL 37344, on coronary flow and contractility in isolated guinea pig heart

The functional role of beta(3)-adrenergic receptors in the heart is still not clear. The actions of two widely used beta(3)-adrenoceptor agonists, such as BRL 37344 and CGP 12177, were studied in the isolated guinea pig heart, perfused at constant pressure according to the Langendorff technique. Heart contractility (dP/dt, first derivative of pressure measured over time) and coronary flow (CF) were assessed simultaneously. BRL 37344 and CGP 12177A at a concentration range of 10-8-10-5 M increased dP/dt and CF. The selective beta(3)-antagonist L-748337 (10-6 M) did not significantly influence either BRL 37344 or CGP 12177A-induced responses. However, both dP/dt and CF responses to BRL 37344 and CGP 12177A at a concentration of 10-7 M were abolished in the presence of the beta(1)/beta(2)-antagonist nadolol (10-5 M). In contrast, cardiovascular responses to CGP 12177A at a higher concentration of 10-5 M were hardly inhibited by nadolol (10-5 M). In addition, BRL 37344 and CGP 12177A at concentrations as low as 10-8 M almost completely abolished an isoprenaline-induced increase in contractility, suggesting that both BRL 37344 and CGP 12177A display beta(1)-antagonistic properties. These data suggest that the stimulatory cardiovascular responses to BRL 37344 at a full range of concentrations, and CGP 12177A at a low concentration of 10-7 M, are not mediated by beta(3)-adrenergic receptors, but rather by activation of beta(1)- or beta(2)-adrenergic receptors. Cardiovascular effects of CGP 12177A at a high concentration of 10-5 M are independent of beta(1)/beta(2)/beta(3)-adrenergic receptors. Summing up, it seems that in the isolated guinea pig heart the functional role of beta(3)-adrenoceptors is not significant. Nonetheless, BRL 37344 and CGP 12177A are not ideal tools for investigation of beta(3)-adrenergic receptor-dependent effects, because these compounds interact with other types of beta-adrenergic receptors.

Evidence against beta 3-adrenoceptors or low affinity state of beta 1-adrenoceptors mediating relaxation in rat isolated aorta

1 The presence of beta(3)-adrenoceptors and the low affinity state of the beta(1)-adrenoceptor (formerly "putative beta(4)-adrenoceptor") was investigated in ring preparations of rat isolated aorta preconstricted with phenylephrine or prostaglandin F(2alpha) (PGF(2alpha)). Relaxant responses to isoprenaline, selective beta(3)-adrenoceptor agonists (BRL 37344, SR 58611A, CL 316243) and non-conventional partial agonists (CGP 12177A, cyanopindolol, pindolol) were obtained. 2 In phenylephrine-constricted, but not PGF(2alpha)-constricted rings, relaxations to isoprenaline showed a propranolol-resistant component. 3 In phenylephrine-constricted rings, relaxations to BRL 37344 (pEC(50), 4.64) and SR 58611A (pEC(50), 4.94) were not antagonized by the selective beta(3)-adrenoceptor antagonist SR 59230A (< or =1 microM). CL 316243 (< or =100 microM) failed to produce relaxation. In PGF(2alpha)-constricted rings only SR 58611A produced relaxation, which was not affected by SR 59230A (< or =3 microM). 4 Non-conventional partial agonists produced relaxation in phenylephrine-constricted but not PGF(2alpha)-constricted rings. The relaxation to CGP 12177A was unaffected by SR 59230A (< or =1 microM) or by CGP 20712A (10 microM), reported to block the low affinity state of the beta(1)-adrenoceptor. 5 beta-adrenoceptor antagonists also produced relaxation in phenylephrine-constricted rings with an order of potency of (pEC(50) values): bupranolol (5.5) approximately 38;SR 59230A (5.47) approximately 38;cyanopindolol (5.47)>pindolol (5.30)>alprenolol (5.10)>propranolol (4.83)>ICI 118551 (4.60)>CGP 12177A (4.38) approximately 38;CGP 20712A (4.35). Bupranolol (100 microM), alprenolol (30 microM), propranolol (100 microM) and SR 59230A (10 microM) produced no relaxation in PGF(2alpha)-constricted rings. 6 These results provide no evidence for the presence of functional beta(3)-adrenoceptors or the low affinity state of the beta(1)-adrenoceptor in rat aorta.

Beta(2)-adrenergic receptor gene delivery to the endothelium corrects impaired adrenergic vasorelaxation in hypertension

BACKGROUND

Impaired beta-adrenergic receptor (AR)-mediated vasorelaxation in hypertension plays a role in increased peripheral vascular resistance and blood pressure. Because the beta(2)AR is the most abundant vascular AR subtype, we sought to enhance betaAR vasorelaxation by overexpressing beta(2)ARs via adenoviral-mediated gene transfer (ADbeta(2)AR) to the vascular endothelium of the carotid artery.

METHODS AND RESULTS

In normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats, we exposed the right common carotid artery to ADbeta(2)AR in situ for 15 minutes by injection into the lumen while the blood flow was interrupted. Control carotids received an empty vector (ADempty). Three days later, transgene expression and selective endothelial localization were confirmed in infected vessels. Vasoregulation after beta(2)AR overexpression (2-fold) was studied in isolated organ baths. ADbeta(2)AR carotid responses to alpha(1)AR and alpha(2)AR agonists were not affected, whereas responses to epinephrine were altered and betaAR-mediated vasorelaxation was enhanced after beta(2)AR overexpression. As expected, betaAR-mediated vasodilatation in control carotids of SHR rats was significantly less than in similar control WKY carotid arteries. ADbeta(2)AR treatment enhanced betaAR vasorelaxation in SHR to levels similar to those seen in ADbeta(2)AR WKY carotids.

CONCLUSIONS

Our results demonstrate a critical role for the endothelium in betaAR-mediated vasorelaxation and suggest that impaired betaAR signaling may account for dysfunctional betaAR vasorelaxation in hypertension rather than impaired endothelium-dependent nitric oxide metabolism.

BRL 37344 inhibited adrenergic transmission in the rat portal vein via atypical beta-adrenoceptors

The effect of BRL 37344, a beta(3)-adrenergic agonist on adrenergic transmission in isolated segments of the rat portal vein was examined in this study. BRL 37344 (10(-9) - 10(-5)M) produced concentration-dependent inhibition of electrically induced contractions. This inhibitory effect of BRL 37344 was not antagonized by propranolol ( 10(-6)M). Isoprenaline ( 10(-9) - 10(-4)M) also produced a concentration-dependent inhibition of electrically induced contractions in the portal vein. Propranolol (10(-6)M) antagonized isoprenaline responses with a -logK(B) value of 8.14 +/- 0.32. BRL 37344-induced inhibition of electrically induced contractions was also unaffected by cyanopindolol (10(-6)M). Isoprenaline but not BRL 37344 significantly reduced noradrenaline-induced contractions of the rat portal vein. CGP12177A produced propranolol-resistant inhibition of electrically induced contractions of the rat portal vein. It was therefore concluded that BRL 37344 inhibited adrenergic transmission in the rat portal vein via atypical beta -adrenoceptors located prejunctionally.

Endothelial adrenoceptors

alpha2 -Adrenergic agonists cause endothelium-dependent relaxation in a number of isolated blood vessels. This effect is explained by the activation of endothelial alpha 2 -adrenoceptors linked to nitric oxide synthase by G i -coupling proteins. The endothelial response to alpha 2 -adrenergic agonists is blunted considerably after regeneration of the endothelium and in atherosclerotic arteries. The relaxation of isolated arteries caused by beta-adrenergic agonists is reduced by removal of the endothelium and, in most cases, by inhibitors of the l -arginine nitric oxide pathway. Likewise, in the intact animal and in the human forearm the vasodilatation to beta 2 -adrenergic agonists is blunted by inhibitors of nitric oxide synthase. Whether these findings reflect the presence of functional beta-adrenoceptors on the endothelium remains controversial. Several beta-adrenergic blockers cause endothelium-dependent relaxation in vitro or augment the production of nitric oxide in vivo. However, these responses cannot be attributed to interactions with endothelial beta-adrenoceptors.

Release of endothelial nitric oxide in coronary arteries by celiprolol, a beta(1)-adrenoceptor antagonist: possible clinical relevance

Mechanisms underlying celiprolol-induced vasodilatation were analyzed in isolated porcine coronary arteries. Celiprolol induced dose-related relaxation of the artery rings with endothelium, an effect which was suppressed by N(G)-nitro-L-arginine methylester (L-NAME), nitric oxide (NO) scavenger, guanylate cyclase inhibitor, endothelium denudation, and removal of Ca(2+). L-NAME contracted, and superoxide dismutase relaxed, the arteries only when the endothelium was preserved. Neither superoxide dismutase nor beta-adrenoceptor antagonists changed celiprolol-induced relaxations. Celiprolol increased the cyclic GMP content in the tissue. The release of NO from endothelium, estimated by the extracellular production of cyclic GMP in arteries incubated in medium containing guanylate cyclase and GTP, was augmented by celiprolol, and L-NAME abolished this action of celiprolol. It is concluded that celiprolol elicits relaxation by acting on sites other than beta-adrenoceptors in the endothelium and by releasing NO, which activates soluble guanylate cyclase in smooth muscle and produces cyclic GMP. Scavenging of superoxide anions from the endothelium does not seem to account for the induced relaxation.

beta-Adrenergic receptor stimulation of L-type Ca2+ channels in rabbit portal vein myocytes involves both alphas and betagamma G protein subunits

1. Previous studies have shown that purified G protein alphas and betagamma subunits stimulate vascular L-type Ca2+ channels through protein kinase A and C (PKA and PKC), respectively. The present study tested whether activation of endogenous G proteins via beta-adrenergic receptor binding also stimulates vascular Ca2+ channels through both Galphas and Gbetagamma and the subsequent activation of PKA and PKC. 2. Peak Ba2+ current (IBa) in freshly isolated rabbit portal vein smooth muscle cells was significantly increased by bath application of 0.5 microM isoproterenol (isoprenaline; ISO) when measured using the whole-cell patch clamp method (53 +/- 3 % increase, n = 15). Stimulation of IBa by ISO was partially reversed by a PKA inhibitor, KT 5720, or a PKC inhibitor, calphostin C, and completely blocked when cells were pretreated with both KT 5720 and calphostin C. 3. Dialysis of cells with polyclonal antibody to Galphas significantly reduced but did not completely eliminate ISO-induced stimulation of IBa. The remaining stimulation was abolished by calphostin C. Dialysis of cells with a polyclonal antibody to Gbeta also significantly reduced ISO-induced stimulation and the remaining stimulation was abolished by KT 5720. Dialysis of cells with both antibodies completely prevented the stimulation of IBa by ISO. 4. ISO-induced stimulation of IBa was reversed by ICI-118,551, a specific beta2-adrenoceptor antagonist, but not by CGP 20712A, a specific beta1-adrenoceptor antagonist. In addition, the beta2-adrenoceptor agonist zinterol significantly increased peak IBa while the beta1-adrenoceptor agonist dobutamine and beta3-adrenoceptor agonist BRL 37344A had little effect on peak IBa. 5. These data suggest that beta-adrenergic receptor stimulation of vascular L-type Ca2+ channels involves both alphas and betagamma G-protein subunits, which exert their effects through PKA and PKC, respectively.

Vascular responses to beta-adrenoceptor subtype-selective agonists with and without endothelium in rat common carotid arteries

1. Using the cannula inserting method, vasodilator responses to beta-adrenoceptor agonists (isoprenaline, denopamine and procaterol) were investigated in isolated and perfused rat common carotid arteries. 2. Each beta-adrenoceptor agonist induced a vasodilation in preparations preconstricted by phenylephrine in a dose-related manner. The potencies were in the order of isoprenaline > procaterol >> denopamine. 3. Denopamine-induced dilations were significantly inhibited by 1 nmol betaxolol (a selective beta1-adrenoceptor antagonist), but it was not influenced by 1 nmol ICI 118,551 (a selective beta2-adrenoceptor antagonist). On the other hand, procaterol-induced vasodilations were significantly inhibited by 1 nmol ICI 118,551 but not modified by 10 nmol betaxolol. 4. ACh-induced vasodilations disappeared after intraluminal saponin injection to remove endothelium, but procaterol- and denopamine-induced dilations were not modified by removal of the endothelium. 5. Pretreatment with L-NG-nitroarginine methyl ester (L-NAME) readily inhibited ACh-induced vasodilations. However, neither procaterol- or denopamine-induced vasodilation was modified by L-NAME treatment. 6. From these results, it is concluded that in the rat common carotid arteries (1) there are abundant beta2- and a few beta1-adrenoceptors, and (2) there is no participation of the endothelium-dependent mechanism in beta-adrenoceptor mediated vasodilations.

Role of endothelium/nitric oxide in atypical beta-adrenoceptor-mediated relaxation in rat isolated aorta

The role of endothelium in the modulation of classical and atypical beta-adrenoceptor-mediated vasorelaxation was investigated in ring preparations of rat isolated thoracic aorta. Rings were pre-constricted with a sub-maximal concentration of noradrenaline (1 microM) and relaxant responses to cumulative concentrations of beta-adrenoceptor agonists obtained. Endothelium removal or pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM) or 1H-[1,2,4] oxadiazolol[4,3,-a] quinoxalin-1-one (ODQ, 10 microM) significantly reduced the relaxant effects of isoprenaline, but had less effect on relaxant responses to the atypical beta-adrenoceptor agonist, (+/-)-4-(3-t-butylamino-2-hydroxypropoxy)-benzimidazol-2-one hydrochloride (CGP 12177A). Sodium nitroprusside (3 nM) shifted the isoprenaline concentration-response curve to the left and restored the attenuated responses in the presence of L-NAME back to control levels. Sodium nitroprusside had little effect on the CGP 12177A concentration-response curve. The results show that the endothelium/nitric oxide (NO) pathway modulates beta-adrenoceptor-mediated vasorelaxation in rat aorta and that classical beta-adrenoceptors are modulated to a greater extent than atypical beta-adrenoceptors.

Beta 1-, beta 2- and atypical beta-adrenoceptor-mediated relaxation in rat isolated aorta

beta-adrenoceptor-mediated relaxation was investigated in ring preparations of rat isolated thoracic aorta. Rings were pre-constricted with a sub-maximal concentration of noradrenaline (1 microM) and relaxant responses to cumulative concentrations of beta-adrenoceptor agonists obtained. The concentration-response curve (CRC) to isoprenaline was shifted to the right by propranolol (0.3 microM) with a steepening of the slope. Estimation of the magnitude of the shift from EC(50) values gave a pA(2) of 7.6. Selective beta(1)- and beta(2)-adrenoceptor antagonists, CGP 20712A (0.1 microM) and ICI 118551 (0.1 microM), respectively, produced 4 and 14 fold shifts of the isoprenaline CRC. Atypical beta-adrenoceptor agonists also produced concentration-dependent relaxation of aortic rings. The order of potency of the beta-adrenoceptor agonists was (-log EC(50)): isoprenaline (6. 25)>cyanopindolol (5.59)>isoprenaline+propranolol (5.11)>CGP 12177A (4.40)>ZD 2079 (4.24)>ZM 215001 (4.07)>BRL 37344 (3.89). Relaxation to CGP 12177A and ZM 215001 was unaffected by propranolol (0.3 microM). SR 59230A ( Collapse

Key Words

• atypical β-adrenoceptors
• β₃-adrenoceptors
• β₄-adrenoceptors
• β₁-adrenoceptors
• β₂-adrenoceptors
• vascular smooth muscle
• rat aorta

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MESH Headings

• Acetylcholine/pharmacology
• Adrenergic alpha-Agonists/pharmacology
• Adrenergic beta-Agonists/pharmacology
• Adrenergic beta-Antagonists/pharmacology
• Animals
• Aorta, Thoracic/drug effects
• Aorta, Thoracic/physiology
• Bupranolol/pharmacology
• Dose-Response Relationship, Drug
• Imidazoles/pharmacology
• In Vitro Techniques
• Isoproterenol/pharmacology
• Male
• Muscle Relaxation/drug effects
• Muscle Relaxation/physiology
• Muscle, Smooth, Vascular/drug effects
• Muscle, Smooth, Vascular/physiology
• Norepinephrine/pharmacology
• Pindolol/analogs & derivatives
• Pindolol/pharmacology
• Propanolamines/pharmacology
• Propranolol/pharmacology
• Rats
• Rats, Wistar
• Receptors, Adrenergic, beta/classification
• Receptors, Adrenergic, beta/physiology
• Receptors, Adrenergic, beta-1/physiology
• Receptors, Adrenergic, beta-2/physiology
• Substrate Specificity
• Vasodilator Agents/pharmacology

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Affiliation(s)

L Brawley School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow G4 0BA
A M Shaw School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow G4 0BA
A MacDonald School of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow G4 0BA

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