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α2-adrenoceptors, (α2A, α2B and α2C-subtypes), are Gi-coupled receptors. Central activation of brain α2A and α2C-adrenoceptors is the main site for α2-agonist mediated clinical responses in hypertension, ADHD, muscle spasm and ITU management of sedation, reduction in opiate requirements, nausea and delirium. However, despite having the same Gi-potency in functional assays, some α2-agonists also stimulate Gs-responses whilst others do not. This was investigated. Agonist responses to 49 different α-agonists were studied (CRE-gene transcription, cAMP, ERK1/2-phosphorylation and binding affinity) in CHO cells stably expressing the human α2A, α2B or α2C-adrenoceptor, enabling ligand intrinsic efficacy to be determined (binding KD/Gi-IC50). Ligands with high intrinsic efficacy (e.g., brimonidine and moxonidine at α2A) stimulated biphasic (Gi-Gs) concentration responses, however for ligands with low intrinsic efficacy (e.g., naphazoline), responses were monophasic (Gi-only). ERK1/2-phosphorylation responses appeared to be Gi-mediated. For Gs-mediated responses to be observed, both a system with high receptor reserve and high agonist intrinsic efficacy were required. From the Gi-mediated efficacy ratio, the degree of Gs-coupling could be predicted. The clinical relevance and precise receptor conformational changes that occur, given the structural diversity of compounds with high intrinsic efficacy, remains to be determined. Comparison with α1 and β1/β2-adrenoceptors demonstrated subclass affinity selectivity for some compounds (e.g., α2:dexmedetomidine, α1:A61603) whilst e.g., oxymetazoline had high affinity for both α2A and α1A- subtypes, compared to all others. Some compounds had subclass selectivity due to selective intrinsic efficacy (e.g., α2:brimonidine, α1:methoxamine/ etilefrine). A detailed knowledge of these agonist characteristics is vital for improving computer- based deep- learning and drug design. [ABSTRACT FROM AUTHOR]

α2‐Adrenoceptors, subdivided into α2A, α2B, and α2C subtypes and expressed in heart, blood vessels, kidney, platelets and brain, are important for blood pressure, sedation, analgesia, and platelet aggregation. Brain α2C‐adrenoceptor blockade has also been suggested to be beneficial for antipsychotic action. However, comparing α2‐adrenoceptor subtype affinity is difficult due to significant species and methodology differences in published studies. Here, 3H‐rauwolscine whole cell binding was used to determine the affinity and selectivity of 99 α‐antagonists (including antidepressants and antipsychotics) in CHO cells expressing human α2A, α2B, or α2C‐adrenoceptors, using an identical method to β and α1‐adrenoceptor measurements, thus allowing direct human receptor comparisons. Yohimbine, RX821002, RS79948, and atipamezole are high affinity non‐selective α2‐antagonists. BRL44408 was the most α2A‐selective antagonist, although its α1A‐affinity (81 nM) is only 9‐fold greater than its α2C‐affinity. MK‐912 is the highest‐affinity, most α2C‐selective antagonist (0.15 nM α2C‐affinity) although its α2C‐selectivity is only 13‐fold greater than at α2A. There are no truely α2B‐selective antagonists. A few α‐ligands with significant β‐affinity were detected, for example, naftopidil where its clinical α1A‐affinity is only 3‐fold greater than off‐target β2‐affinity. Antidepressants (except mirtazapine) and first‐generation antipsychotics have higher α1A than α2‐adrenoceptor affinity but poor β‐affinity. Second‐generation antipsychotics varied widely in their α2‐adrenoceptor affinity. Risperidone (9 nM) and paliperidone (14 nM) have the highest α2C‐adrenoceptor affinity however this is only 5‐fold selective over α2A, and both have a higher affinity for α1A (2 nM and 4 nM, respectively). So, despite a century of yohimbine use, and decades of α2‐subtype studies, there remains plenty of scope to develop α2‐subtype selective antagonists. [ABSTRACT FROM AUTHOR]

Abstract Highly selective drugs offer a way to minimize side‐effects. For agonist ligands, this could be through highly selective affinity or highly selective efficacy, but this requires careful measurements of intrinsic efficacy. The α1‐adrenoceptors are important clinical targets, and α1‐agonists are used to manage hypotension, sedation, attention deficit hypersensitivity disorder (ADHD), and nasal decongestion. With 100 years of drug development, there are many structurally different compounds with which to study agonist selectivity. This study examined 62 α‐agonists at the three human α1‐adrenoceptor (α1A, α1B, and α1D) stably expressed in CHO cells. Affinity was measured using whole‐cell 3H‐prazosin binding, while functional responses were measured for calcium mobilization, ERK1/2‐phosphorylation, and cAMP accumulation. Efficacy ratios were used to rank compounds in order of intrinsic efficacy. Adrenaline, noradrenaline, and phenylephrine were highly efficacious α1‐agonists at all three receptor subtypes. A61603 was the most selective agonist and its very high α1A‐selectivity was due to selective α1A‐affinity (>660‐fold). There was no evidence of Gq‐calcium versus ERK‐phosphorylation biased signaling at the α1A, α1B, or α1D‐adrenoceptors. There was little evidence for α1A calcium versus cAMP biased signaling, although there were suggestions of calcium versus cAMP bias the α1B‐adrenoceptor. Comparisons of the rank order of ligand intrinsic efficacy suggest little evidence for selective intrinsic efficacy between the compounds, with perhaps the exception of dobutamine which may have some α1D‐selective efficacy. There seems plenty of scope to develop affinity selective and intrinsic efficacy selective drugs for the α1‐adrenoceptors in future.

Highly selective drugs offer a way to minimize side‐effects. For agonist ligands, this could be through highly selective affinity or highly selective efficacy, but this requires careful measurements of intrinsic efficacy. The α1‐adrenoceptors are important clinical targets, and α1‐agonists are used to manage hypotension, sedation, attention deficit hypersensitivity disorder (ADHD), and nasal decongestion. With 100 years of drug development, there are many structurally different compounds with which to study agonist selectivity. This study examined 62 α‐agonists at the three human α1‐adrenoceptor (α1A, α1B, and α1D) stably expressed in CHO cells. Affinity was measured using whole‐cell 3H‐prazosin binding, while functional responses were measured for calcium mobilization, ERK1/2‐phosphorylation, and cAMP accumulation. Efficacy ratios were used to rank compounds in order of intrinsic efficacy. Adrenaline, noradrenaline, and phenylephrine were highly efficacious α1‐agonists at all three receptor subtypes. A61603 was the most selective agonist and its very high α1A‐selectivity was due to selective α1A‐affinity (>660‐fold). There was no evidence of Gq‐calcium versus ERK‐phosphorylation biased signaling at the α1A, α1B, or α1D‐adrenoceptors. There was little evidence for α1A calcium versus cAMP biased signaling, although there were suggestions of calcium versus cAMP bias the α1B‐adrenoceptor. Comparisons of the rank order of ligand intrinsic efficacy suggest little evidence for selective intrinsic efficacy between the compounds, with perhaps the exception of dobutamine which may have some α1D‐selective efficacy. There seems plenty of scope to develop affinity selective and intrinsic efficacy selective drugs for the α1‐adrenoceptors in future.Comparisons of the rank order of ligand intrinsic efficacy suggests little evidence for selective intrinsic efficacy between agonists for the three human α1‐adrenoceptors. [ABSTRACT FROM AUTHOR]

The role of stress effector systems in the initiation and progression of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), the most commonly used experimental model of MS, has strongly been suggested. To corroborate this notion, alterations in activity of the sympathoadrenal and sympathoneural axes of sympathoadrenal system (a major communication pathway between the central nervous system and the immune system), mirrored in altered release of their end-point mediators (adrenaline and noradrenaline, respectively), are shown to precede (in MS) and/or occur during development of MS and EAE in response to immune cell activation (in early phase of disease) and disease-related damage of sympathoadrenal system neurons and their projections (in late phase of disease). To add to the complexity, innate immunity cells and T-lymphocytes synthesize noradrenaline that may be implicated in a local autocrine/paracrine self-amplifying feed-forward loop to enhance myeloid-cell synthesis of proinflammatory cytokines and inflammatory injury. Furthermore, experimental manipulations targeting noradrenaline/adrenaline action are shown to influence clinical outcome of EAE, in a disease phase-specific manner. This is partly related to the fact that virtually all types of cells involved in the instigation and progression of autoimmune inflammation and target tissue damage in EAE/MS express functional adrenoceptors. Although catecholamines exert majority of immunomodulatory effects through β2-adrenoceptor, a role for α-adrenoceptors in EAE pathogenesis has also been indicated. In this review, we summarize all aforementioned aspects of immunopathogenetic action of catecholamines in EAE/MS as possibly important for designing new strategies targeting their action to prevent/mitigate autoimmune neuroinflammation and tissue damage.

Yanwen Zhou,* Ying Liu,* Yunhua Hao, Ya Feng, Lizhen Pan, Wuchao Liu, Bing Li, Libin Xiao, Lingjing Jin, Zhiyu Nie Department of Neurology, Shanghai Tongji Hospital, Tongji University School of Medicine, Shanghai 200065, China *These authors contributed equally to this work Background: Botulinum neurotoxin type A (BoNT/A) is emerging as a treatment modality for Raynaud’s phenomenon (RP). However, the mechanism of the role of BoNT/A in antagonizing the constriction of arteriola in RP remains unclear. Materials and methods: We tested the constriction of arteriole diameter and the distribution of adrenergic receptors on the rat cremaster modle. Moreover, we measured the secretion of norepinephrine (NE), protein level changes and related receptors on cultured rat superior cervical ganglia neurons(SCGNs), a model of sympathetic neuron. Results: Based on our results, the inhibition of arteriole vasoconstriction was increased with increasing doses of BoNT/A. BoNT/Α, prazosin, and BQ123 treatment can result in significant inhibition of arteriole vasoconstriction with the same electrical stimulation. The inhibition effect of prazosin was equivalent to BoNT/A, while BQ123 has a synergistic effect with BoNT/A. After treating SCGNs using BoNT/A for 30 min, the decrease in fluorescence intensity of FM1-43 slowed down which was correlated with the doses of BoNT/A. Furthermore, release of NE in the supernatant was significantly decreased as measured by enzyme-linked immunosorbent assay, 24 h after a high dose of BoNT/A (25 µ/mL). Cleaved-SNAP-25 was detected by western blotting 24 h following BoNT/A (50 µ/mL) treatment. Moreover, receptor SV2C, GM1, and FGFR3 were detected on sympathetic neurons, similarly to cholinergic neurons. Conclusion: Our study showed that BoNT/A could significantly inhibit electrical stimulation-induced arteriole vasoconstriction through the sympathetic pathway. The mechanism was similar to the cholinergic one, in which the vesicle release of sympathetic neurons could be inhibited by cleavage of SNAP-25. The end result was blocked vesicle fusion with the presynaptic membrane after BoNT/A treatment, inhibiting the release of the NE. Keywords: botulinum neurotoxin type A, Raynaud’s phenomenon, α-adrenoceptor, arteriole diameter constrict rate, SNAP-25, SV2C, GM1, FGFR3, sympathetic neuron, vesicle cycle

The role of stress effector systems in the initiation and progression of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), the most commonly used experimental model of MS, has strongly been suggested. To corroborate this notion, alterations in activity of the sympathoadrenal and sympathoneural axes of sympathoadrenal system (a major communication pathway between the central nervous system and the immune system), mirrored in altered release of their end-point mediators (adrenaline and noradrenaline, respectively), are shown to precede (in MS) and/or occur during development of MS and EAE in response to immune cell activation (in early phase of disease) and disease-related damage of sympathoadrenal system neurons and their projections (in late phase of disease). To add to the complexity, innate immunity cells and T-lymphocytes synthesize noradrenaline that may be implicated in a local autocrine/paracrine self-amplifying feed-forward loop to enhance myeloid-cell synthesis of proinflammatory cytokines and inflammatory injury. Furthermore, experimental manipulations targeting noradrenaline/adrenaline action are shown to influence clinical outcome of EAE, in a disease phase-specific manner. This is partly related to the fact that virtually all types of cells involved in the instigation and progression of autoimmune inflammation and target tissue damage in EAE/MS express functional adrenoceptors. Although catecholamines exert majority of immunomodulatory effects through β2-adrenoceptor, a role for α-adrenoceptors in EAE pathogenesis has also been indicated. In this review, we summarize all aforementioned aspects of immunopathogenetic action of catecholamines in EAE/MS as possibly important for designing new strategies targeting their action to prevent/mitigate autoimmune neuroinflammation and tissue damage. [ABSTRACT FROM AUTHOR]

Abstract Strength training induces not only muscle growth but also increased bone strength, a change that is expected to be associated with increased bone blood flow. However, the effects of exercise on contractile properties of bone microvascultaure have not been investigated. Once-a-week strength training with electrical muscle stimulation was applied unilaterally to tibialis anterior muscle of guinea pigs, while muscle force was measured from both legs to compare their muscle strength and endurance. After 10 weeks of training, changes in the arteriolar diameters of isolated periosteum taken from both trained and non-trained legs were measured using a video tracking system. Electrical field stimulation evoked a phasic constriction followed by a sustained dilatation in periosteal arterioles of trained legs, while triggering only vasoconstriction in the arterioles of non-trained legs. In trained leg arterioles, phentolamine, an α-adrenoceptor antagonist, inhibited both the constriction and dilatation. Prazosin, an α 1 -adrenoceptor antagonist, inhibited only the constriction, while yohimbine, α 2 -adrenoceptor antagonist, or l -nitro arginine (L-NA), a nitric oxide (NO) synthase inhibitor, inhibited the dilatation. In non-trained leg arterioles, phentolamine or prazosin largely suppressed the constriction, but failed to unmask any dilatation. Consistently, noradrenaline (NAd)-induced arteriolar constriction was enhanced and prolonged by L-NA in trained but not non-trained side arterioles. Thus, NAd released from sympathetic nerves appears to activate endothelial α 2 -adrenoceptors to release NO resulting in the sustained dilatation of periosteum arterioles from trained leg. The altered sympathetic vasomotor function would facilitate the blood supply to the bone and may contribute to the exercise-induced bone strength gain. Highlights • Unilateral forced exercise of guinea-pig leg muscle develops sympathetic vasodilation in periosteal arterioles of trained but not non-trained legs. • The sympathetic vasodilatation in trained leg arterioles is mediated by endothelial but not neuronal nitric oxide. • The exercise appears to up-regulate endothelial α 2 -adrenoreceptor linked with nitric oxide release. • The exercise-induced sympathetic vasodilatation would facilitate bone blood supply and may contribute to the exercise-induced bone strength gain. [ABSTRACT FROM AUTHOR]

Effect of pathological prolongation of action potential duration on the α-adrenoceptor-mediated negative inotropy was studied in streptozotocin-induced diabetic mice myocardium. In streptozotocin-treated mouse ventricular myocardium, which had longer duration of action potential than that in control mice, the negative inotropic response induced by phenylephrine was smaller than that in control mice. 4-Aminopyridine prolonged the action potential duration and decreased the negative inotropy in control mice. Cromakalim shortened the action potential duration and increased the negative inotropy in streptozotocin-treated mice. These results suggest that the reduced α-adrenoceptor-mediated inotropy in the diabetic mouse myocardium is partly due to its prolonged action potential.

Purpose The aim of this study is to evaluate the effect of retigabine on the smooth muscle response to acetylcholine, adrenaline, α-and β-adrenoceptor agonists. Methods We studied the change in the spontaneous smooth muscle contraction of guinea pig gastric corpus strips before and after 20-min treatment with 2 μM retigabine. We also evaluated the effect of retigabine on the smooth muscle response to 10 μM acetylcholine, 1 and 10 μM adrenaline, 1 μM methoxamine, 0.1 μM p-iodoclonidine and 10 μM isoproterenol. Results We observed a significant reduction in the effects of all studied mediators and agonists when they were added to organ baths in the presence of retigabine. Retigabine diminished the effect of acetylcholine on the spontaneous smooth muscle activity. The effect was fully antagonized by XE-991 (Kv7 channel blocker), which supports our hypothesis about the role of KCNQ channels in the registered changes. The increase in the contraction force after adding of 1 μM adrenaline, methoxamine, and 0.1 μM p-iodoclonidine was also significantly smaller in presence of retigabine. However, comparing the effect of 10 μM adrenaline on the contractility before and after treatment with retigabine, we observed increased contractility when retigabine was present in the organ baths. Conclusion A possible explanation for the observed diminished effects of mediators and receptor agonists is that the effect of retigabine on smooth muscle contractility is complex. The membrane hyperpolarization, the interaction between Kv7 channels and adrenoceptors, and the influence on signaling pathways may contribute to the summary smooth muscle response. [ABSTRACT FROM AUTHOR]

Background: β-blockers offer the first line therapy in congenital long QT syndrome (LQTS), and are more effective to prevent the cardiac event in LQTS type 1 than in type 2 or 3. In contrast, left cardiac sympathetic denervation (LCS D) was shown to be highly effective in patients refractory to β-blockers. Total sympathetic ablation by LCSD indicates the addititional involvement of α-adr enoceptor-mediated pathway. In genotyped LQT2 patients, we therefore hypothesized that blockade of α-adrenoceptor in addition to α-adrenoceptor by carvedilol could reduce cardiac events more efficiently than other types of β-blockers. Methods and Results: The study population consisted of 51 genotyped LQT2 patients (18 males, 23 ± 11years old). They were divided into 2 groups (group 1: 43 patients treated with selective β-blockers, group 2: 8 patients with carvedilol) and retrospectively analyzed the efficacy of the respective β-blocker therapy in suppressing cardiac events. Cardiac events were observed in 11 patients of group 1 (26%) but none in group 2 during a follow-up period of 83 ± 80 months (P = 0.098). Conclusions: Carvedilol may be a potentially beneficial therapy for genotyped LQT2 patients who are refractory to other β selective blockers.

Rationale: No validated methods have been available for studying brain noradrenergic neurotransmission in vivo in humans. Positron emission tomography (PET) radiotracers are widely used in clinical drug development targeted to brain receptors and can also in some cases be employed to monitor extracellular (synaptic) neurotransmitter concentrations. Objectives: The objective of this study is to test the sensitivity of [C]ORM-13070 uptake to increased concentrations of extracellular (synaptic) noradrenaline in the human brain. Methods: Eight subjects underwent a control PET scan with [C]ORM-13070, a subtype-selective α-adrenoceptor antagonist radioligand, and two PET scans after two different noradrenaline challenges, i.e. during ketamine infusion and after a dose of atomoxetine combined with cold stimulation. Tracer uptake in the caudate nucleus and putamen was described with AUC values in scan time windows of 10-20 and 5-30 min post injection and quantified with the ratio method. Voxel-based analysis was performed with average bound per free (B/F) ratio images. Results: Both noradrenaline challenges were consistently associated with 10-20 % ( p < 0.05) reductions in tracer uptake in the dorsal striatum, as determined with region-of-interest-based analysis. Voxel-based analysis revealed significant reductions in B/F ratios in the dorsal striatum, in the brain stem and in several cortical areas. Reductions of 24 and 23 % were detected in the peak putamen clusters with ketamine and atomoxetine + cold, respectively. Conclusion: Direct experimental support was gained for the suitability of [C]ORM-13070 for imaging of brain noradrenergic neurotransmission. [ABSTRACT FROM AUTHOR]

Purpose: Dexmedetomidine acts as a selective α-adrenergic receptor agonist and an imidazoline receptor agonist, both of which are known to affect insulin secretion. Here, we investigated the effects of clinically relevant concentrations of dexmedetomidine on insulin secretion under in vivo conditions. Furthermore, its underlying mechanisms were examined using isolated islets in vitro. Methods: For the in vivo oral glucose tolerance test (OGTT), male Sprague-Dawley rats were randomly allocated to one of three groups ( n = 7 in each group): two groups infused with dexmedetomidine at a low (group L) or a high (group H) dose, and one control group infused with the same amount of saline (group C). For the in vitro perifusion study, insulin released from isolated islets was measured during stepwise changes in glucose. Dexmedetomidine (0.1-100 µM) was added to the chamber. Results: During the OGTT test, the insulin levels in group H were significantly lower than those in group C at 30, 60, and 90 min after glucose load. On the other hand, insulin levels in group L were comparable to those of group C at all time points. In the perfusion study, dexmedetomidine inhibited glucose-stimulated insulin secretion in a concentration-dependent manner. When co-treated with yohimbine, an α-adrenoceptor blocker, dexmedetomidine adversely increased glucose-induced insulin secretion. However, co-treatment with idazoxan, an antagonist for α-adrenergic and imidazoline receptors, completely abolished the action of dexmedetomidine. Conclusions: Dexmedetomidine had no effect on insulin secretion at sedative dose, whereas it significantly inhibited insulin secretion at supraclinical high concentrations mainly via the α-adrenoceptor. [ABSTRACT FROM AUTHOR]

Purpose: α-Adrenoceptors share inhibitory presynaptic functions with the more abundant α-adrenoceptor subtype, but they also have widespread postsynaptic modulatory functions in the brain. Research on the noradrenergic system of the human brain has been hampered by the lack of suitable PET tracers targeted to the α-adrenoceptor subtypes. Methods: PET imaging with the specific α-adrenoceptor antagonist tracer [C]ORM-13070 was performed twice in six healthy male subjects to investigate the test-retest reliability of tracer binding. Results: The bound/free ratio of tracer uptake relative to nonspecific uptake into the cerebellum during the time interval of 5 - 30 min was most prominent in the dorsal striatum: 0.77 in the putamen and 0.58 in the caudate nucleus. Absolute test-retest variability in bound/free ratios of tracer ranged from 4.3 % in the putamen to 29 % in the hippocampus. Variability was also <10 % in the caudate nucleus and thalamus. Intraclass correlation coefficients (ICC) ranged from 0.50 in the hippocampus to 0.89 in the thalamus (ICC >0.70 was also reached in the caudate nucleus, putamen, lateral frontal cortex and parietal cortex). The pattern of [C]ORM-13070 binding, as determined by PET, was in good agreement with receptor density results previously derived from post-mortem autoradiography. PET data analysis results obtained with a compartmental model fit, the simplified reference tissue model and a graphical reference tissue analysis method were convergent with the tissue ratio method. Conclusion: The results of this study support the use of [C]ORM-13070 PET in the quantitative assessment of α-adrenoceptors in the human brain in vivo. Reliable assessment of specific tracer binding in the dorsal striatum is possible with the help of reference tissue ratios. [ABSTRACT FROM AUTHOR]

Ethnopharmacological relevance The leaf of Alchornea cordifolia (Euphorbiaceae) is used in traditional African medicine in the treatment of various neurological and psychiatric disorders including depression. Previous studies have shown its potent antidepressant-like effect in the forced swimming test (FST). Hence, this study sought to investigate the involvement of monoaminergic systems in the antidepressant-like effect elicited by hydroethanolic leaf extract of Alchornea cordifolia (HeAC) in the FST. Materials and methods HeAC (25–400 mg/kg, p.o.) was administered 1 h before the FST. To investigate the contribution of monoaminergic systems to antidepressant-like effect, receptors antagonists were injected 15 min before oral administration of HeAC (200 mg/kg) to mice and 1 h thereafter, subjected to FST. Results HeAC (200 and 400 mg/kg, p.o.) produced dose dependent and significant ( P <0.001) antidepressant-like effect, in the FST, without accompanying changes in spontaneous locomotor activities in the open-field test. The anti-immobility effect of HeAC (200 mg/kg) in the FST was prevented by pretreatment of mice with SCH 23390 (0.05 mg/kg, s.c ., a dopamine D 1 receptor antagonist), sulpiride (50 mg/kg, i.p., a dopamine D 2 receptor antagonist), prazosin (1 mg/kg, i.p., an α 1 -adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α 2 -adrenoceptor antagonist), and GR 127993 (5-HT 1B receptor antagonist). Similarly, 3 days intraperitoneal injection of p -chlorophenylalanine ( p CPA, 150 mg/kg, i.p., an inhibitor of serotonin synthesis) prevented the antidepressant-like effect elicited by HeAC . The combination of subeffective doses of imipramine (5 mg/kg, p.o.) or fluoxetine (5 mg/kg , p.o.), with HeAC (25 mg/kg, p.o., subeffective dose) produced a synergistic antidepressant-like effect in the FST. Conclusion The hydroethanolic extract of Alchornea cordifolia possesses antidepressant-like effect mediated through interaction with dopamine (D 1 and D 2 ), noradrenergic (α 1 and α 2 adrenoceptors), and serotonergic (5HT 1B receptors) systems. Also, the potentiation of the anti-immobility effect of conventional antidepressants (fluoxetine and imipramine) by Alchornea cordifolia suggest potential therapeutic effect in depression. [ABSTRACT FROM AUTHOR]

The study examined the dose-dependent effects of selective antagonists of α-, α-, and α- adrenoceptors applied in concentrations of 10-10 M on atrial and ventricular contractility of rat myocardium in vitro. Selective blockade of each α-adrenoceptor subtype affected the contractile force of the atrial and ventricular strips. Various concentrations of α- and α-adrenoceptor antagonists produced positive inotropic effect on ventricular strips and negative effect on atrial strips. α-Adrenoceptor blocker in the majority of the tested concentrations produced a positive inotropic effect in both atria and ventricles. [ABSTRACT FROM AUTHOR]

Purpose: C-labelled 1-[( S)-1-(2,3-dihydrobenzo[1,2]dioxin-2-yl)methyl]-4-(3-methoxy-methylpyridin-2-yl)-piperazine (C-ORM-13070) is a novel PET tracer for imaging of α-adrenoceptors in the human brain. Brain α-adrenoceptors may be therapeutic targets in several neuropsychiatric disorders, including depression, schizophrenia and Alzheimer's disease. To validate the use of C-ORM-13070 in humans, we investigated its radiometabolism, pharmacokinetics, whole-body distribution and radiation dose. Methods: Radiometabolism was studied in a test-retest setting in six healthy men. After intravenous injection of C-ORM-13070, blood samples were drawn over 60 min. Plasma samples were analysed by radio-HPLC for intact tracer and its radioactive metabolites. Metabolite-corrected plasma time-activity curves were used for calculation of pharmacokinetics. In a separate group of 12 healthy men, the whole-body distribution of C-ORM-13070 and radiation exposure were investigated by dynamic PET/CT imaging without blood sampling. Results: Two radioactive metabolites of C-ORM-13070 were detected in human arterial plasma. The proportion of unchanged C-ORM-13070 decreased from 81 ± 4 % of total radioactivity at 4 min after tracer injection to 23 ± 4 % at 60 min. At least one of the radioactive metabolites penetrated into red blood cells, while the parent tracer remained in plasma. The apparent elimination rate constant and corresponding half-life of unchanged C-ORM-13070 in arterial plasma were 0.0117 ± 0.0056 min and 73.6 ± 35.8 min, respectively. The organs with the highest absorbed doses were the liver (12 μSv/MBq), gallbladder wall (12 μSv/MBq) and pancreas (9.1 μSv/MBq). The mean effective dose was 3.9 μSv/MBq, with a range of 3.6 - 4.2 μSv/MBq. Conclusion: C-ORM-13070 was rapidly metabolized in human subjects after intravenous injection. The effective radiation dose of C-ORM-13070 was in the same range as that of other C-labelled brain receptor tracers. An injection of 500 MBq of C-ORM-13070 would expose a subject to 2.0 mSv of radiation. This supports the use of C-ORM-13070 in repeated PET scans, for example, in receptor occupancy trials with novel drug candidates. [ABSTRACT FROM AUTHOR]

The interaction between drugs and receptors is particularly important in revealing the drug acting mechanism and developing new leads. In this work, α-Adrenoceptor ( α-AR) from HEK293 cell line is purified and immobilized on the surface of macro-pore silica gel to prepare an high-performance affinity chromatography stationary phase for the pursuit of drug-receptor interactions by competition zonal elution. Naftopidil is found to have only one type of binding site to α-AR with an association constant of 1.45 × 10 M and a concentration of binding sites of 1.56 × 10 M, while terazosin hydrochloride proves to present two kinds of binding site on the receptor at which the association constants are determined to be 1.61 × 10 M and 2.06 × 10 M, and the corresponding concentrations of the binding sites are 1.56 × 10 M and 1.11 × 10 M, respectively. It is concluded that the stationary phase containing attached α-AR can be used to realize the binding of a drug to the receptor. [ABSTRACT FROM AUTHOR]

Highlights: [•] Expression and activity of IP3 receptor were lost in obese mouse aortae. [•] PKC pathway was impaired in the aortae of obese mice. [•] PKCδ is likely to contribute to phenylephrine-induced contraction in obese mouse aortae. [Copyright &y& Elsevier]

Benign prostatic hyperplasia (BPH) is a progressive disease related to the imbalance of cell growth and apoptosis, and it plays a key role in the development of lower urinary tract symptoms (LUTS). The main pharmacological treatment is based on α-adrenoceptor blockers, but in several cases monotherapy has failed. Recent studies of prostate pathophysiology have noted the role of α-adrenoceptors and 5-HT receptors in prostate cell proliferation in addition to the usual role of α-adrenoceptors in prostate contraction. N-phenylpiperazine is a scaffold structure that may confer drug affinity for these three receptors. Therefore, the present work aimed to investigate the pharmacological characteristics of N1-(2-methoxyphenyl)- N4-hexylpiperazine (LDT66). Using isometric contraction assays with rat prostate and aorta, LDT66 reduced phenylephrine-induced contractions and showed K values of 3.4 and 2.2 nM for α- and α-adrenoceptors, respectively. According to the functional binding assays data, LDT66 showed a high affinity (nanomolar range) for the 5-HT receptors, behaving as an antagonist. LDT66 also showed a low affinity (micromolar range) for receptors unrelated to BPH such as α-adrenoceptors, α-adrenoceptors, muscarinic and 5-HT receptors, which is a desirable profile in order to prevent putative side effects. Accordingly, LDT66 (100 μg/kg) showed a marginal hypotensive effect. Using the DU-145 prostate cells, control experiments characterized the α-adrenoceptor- and 5-HT receptor-mediated cell growth by phenylephrine and 5-HT, respectively. LDT66 (50 nM) prevented both effects similarly. In conclusion, LDT66 is a high-affinity multi-target antagonist of relevant receptors for BPH, and it may be a new starting point for multi-target drug development to treat BPH and LUTS. [ABSTRACT FROM AUTHOR]

α-, α-, and α-adrenoceptors belong to the rhodopsin-like G-protein coupled receptors family. They are integral membrane proteins typified by a bundle of seven transmembrane helices. 50 % of the currently available drugs in the market target G-protein coupled receptors. Crystal structure of α-, α-, and α-adrenoceptors are not yet solved. We performed homology modeling of the human α-, α-, and α-adrenoceptor subtypes based on the crystal structure of the β-adrenergic receptor. Molecular docking studies of five different antagonists toward these receptors revealed receptor subtype selectivity, and which in turn potentially guide in the rational design of subtype selective antagonists. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Alpha1-adrenoceptor (α-AR) antagonists are now considered to be the first-line agents for the management for men with lower urinary tract symptoms associated with benign prostate hyperplasia (LUTS/BPH). A number of α-AR antagonists are currently approved in the United States, Europe and Asia, all of which are generally well tolerated; however, there are differences in the efficacy and adverse effect profiles among the various α-AR antagonists and patients. Recent molecular approaches have provided not only new knowledge about α-AR subtypes (α-, α- and α-AR) but also new strategies to improve the efficacy and reduce the adverse effects of LUTS medical therapy. Precious understanding of the subtype-specific roles of α-AR provides a better strategy for LUTS medical treatment. Additionally, in the future, molecular approaches may enable personalized medicine for LUTS based on individual differences in the genetic background. [ABSTRACT FROM AUTHOR]

Aims/hypothesis: Inspired by recent speculation about the potential utility of α-antagonism in the treatment of type 2 diabetes, the study examined the contribution of α-antagonism vs other mechanisms to the antihyperglycaemic activity of the imidazoline (±)-efaroxan. Methods: Effects of the racemate and its pure enantiomers on isolated pancreatic islets and beta cells in vitro, as well as on hyperglycaemia in vivo, were investigated in a comparative manner in mice. Results: In isolated perifused islets, the two enantiomers of efaroxan were equally potent in counteracting inhibition of insulin release by the ATP-dependent K (K) channel-opener diazoxide but (+)-efaroxan, the presumptive carrier of α-antagonistic activity, was by far superior in counteracting inhibition of insulin release by the α-agonist UK14,304. In vivo, (+)-efaroxan improved oral glucose tolerance at 100-fold lower doses than (−)-efaroxan and, in parallel with observations made in vitro, was more effective in counteracting UK14,304-induced than diazoxide-induced hyperglycaemia. The antihyperglycaemic activity of much higher doses of (−)-efaroxan was associated with an opposing pattern (i.e. with stronger counteraction of diazoxide-induced than UK14,304-induced hyperglycaemia), which implicates a different mechanism of action. Conclusions/interpretation: The antihyperglycaemic potency of (±)-efaroxan in mice is almost entirely due to α-antagonism, but high doses can also lower blood glucose via another mechanism. Our findings call for reappraisal of the possible clinical utility of α-antagonistic compounds in recently identified subpopulations of patients in which a congenitally higher level of α-adrenergic activation contributes to the development and pathophysiology of type 2 diabetes. [ABSTRACT FROM AUTHOR]

Abstract: Activation of coronary vascular α-adrenoceptors results in vasoconstriction which competes with metabolic vasodilation during sympathetic activation. Epicardial conduit vessel constriction is largely mediated by α1-adrenoceptors; the constriction of the resistive microcirculation largely by α2-adrenoceptors, but also by α1-adrenoceptors. There is no firm evidence that α-adrenergic coronary vasoconstriction exerts a beneficial effect on transmural blood flow distribution. In fact, α-blockade in anesthetized and conscious dogs improves blood flow to all transmural layers, during normoperfusion and hypoperfusion. Also, in patients with coronary artery disease, blockade of α1- and α2-adrenoceptors improves coronary blood flow, myocardial function and metabolism. This article is part of a Special Issue entitled “Coronary Blood Flow”. [Copyright &y& Elsevier]

Purposes: The alpha 2 (α)-adrenoceptor is highly important in the antinociception of tramadol administered systemically and intrathecally. However, it is unclear whether tramadol at the spinal level exerts an antinociceptive effect by directly binding with α-adrenoceptors in the spinal cord. This study was conducted to investigate the relationship between α-adrenoceptors and the antinociception of tramadol at the spinal level. Methods: The rat formalin test was designed to determine whether the intrathecal α-adrenoceptor antagonist yohimbine could reverse the antinociceptive effect of intrathecal tramadol. The binding affinity of tramadol for α-adrenoceptors in the spinal cord was determined by radioligand binding assay using the labeled α-adrenoceptor antagonist [H]-yohimbine. Results: The nociceptive test showed that intrathecal tramadol induced significant antinociception whereas pretreatment with intrathecal yohimbine partially reversed this antinociception. Scatchard analysis of the binding data showed [H]-yohimbine had high affinity ( K = 1.79 n M) for the α-adrenoceptor in the rat spinal cord, and that tramadol inhibited specific binding of [H]-yohimbine with the spinal cord membranes with a high affinity constant ( K = 34.14 μ M) and an IC50 of 68.25 μ M, which indicated that tramadol was much less potent than [H]-yohimbine at binding with α-adrenoceptors of the spinal cord. Conclusion: The results suggested that, with very weak binding affinity for α-adrenoceptors, the antinociception of intrathecal tramadol is partially related to α-adrenoceptors, and its intrathecal antinociception may mainly involve its indirect activation of α-adrenoceptors in the spinal cord. [ABSTRACT FROM AUTHOR]

Binding interaction between ligand and G-protein coupled receptor plays an important role in the several steps of exertion of therapeutic effect by a drug and has become increasingly interesting to pharmacists, chemists, biologists and companies. α-Adrenoceptor (α-AR) was purified from cell line which stably expressed α-AR and evenly immobilized on the surface of macroporous silica gel to prepare a novel stationary phase for investigating the interaction between drug and receptor. Control drugs of α-AR including phentolamine, terazosin and urapidil were used to characterize the retention properties of the stationary phase containing the receptor. Further work was performed to calculate the binding sites and association constant of prazosin binding to the immobilized receptor. The results presented a value of 4.55 × 10 M for binding sites and of 2.2 × 10 M for the association constant during the interaction between prazosin and α-AR. The proposed affinity method was stable at least in seven consecutive days, as well as had the primary bioactivities of recognizing and binding the ligand, providing an alternative for representing the interaction between drug and functional protein. [ABSTRACT FROM AUTHOR]

Background: β-blockers offer the first line therapy in congenital long QT syndrome (LQTS), and are more effective to prevent the cardiac event in LQTS type 1 than in type 2 or 3. In contrast, left cardiac sympathetic denervation (LCS D) was shown to be highly effective in patients refractory to β-blockers. Total sympathetic ablation by LCSD indicates the addititional involvement of α-adr enoceptor-mediated pathway. In genotyped LQT2 patients, we therefore hypothesized that blockade of α-adrenoceptor in addition to α-adrenoceptor by carvedilol could reduce cardiac events more efficiently than other types of β-blockers. Methods and Results: The study population consisted of 51 genotyped LQT2 patients (18 males, 23 ± 11years old). They were divided into 2 groups (group 1: 43 patients treated with selective β-blockers, group 2: 8 patients with carvedilol) and retrospectively analyzed the efficacy of the respective β-blocker therapy in suppressing cardiac events. Cardiac events were observed in 11 patients of group 1 (26%) but none in group 2 during a follow-up period of 83 ± 80 months (P = 0.098). Conclusions: Carvedilol may be a potentially beneficial therapy for genotyped LQT2 patients who are refractory to other β selective blockers. [Copyright &y& Elsevier]

Abstract: The human hepatocellular carcinoma (HCC) is a common cancer with high mortality rate. We examined the density and coupling to phospholipase C (PLC) of the α1-adrenoceptors. In HCC liver, the α1-adrenoceptor density – as assessed by [³H]-Prazosin binding – was significantly reduced to about 75% when compared to non-adjacent non-tumorous liver (NA-NL) (P=0.0002). The decrease in maximal α1-adrenoceptor concentration (Bmax) was accompanied by a significant reduction in noradrenaline-stimulated PLC activity (P<0.032 versus NA-NL) (assessed by [³H]-PIP2 hydrolysis). GTPγS-stimulated PLC activity in HCC livers did not statistically differ from NA-NL livers. NaF, which activates all G-proteins, stimulated PLC in both HCC and NA-NL livers to a similar extent. The altered noradrenaline-induced functional responsiveness of HCC livers was not reflected by changes in the binding affinity of [³H]-Prazosin for α1-adrenoceptors (NA-NL: 0.066±0.010pmol/l; tumour: 0.067±0.020pmol/l). These results demonstrate that human HCC causes profound alteration of the hepatic α1-adrenoceptor signal transduction pathway and may account for a negative cancer related metabolism of carbohydrates and wasting syndrome in tumour patients. [Copyright &y& Elsevier]

Abstract: It has recently been shown that clonidine suppresses itch-related responses via its action on α2-adrenoceptors in the spinal cord, raising the possibility that the descending noradrenergic system regulates itch signaling in the spinal cord. In this study, we investigated whether the transmission of itch signals in the spinal cord is under tonic inhibition by the descending noradrenergic system. An intraplantar injection of serotonin in mice induced biting of the treated paw (an itch-related response). An intrathecal injection of 6-hydroxydopamine (catecholaminergic neurotoxin) enhanced the itch-related response. There was a significant inverse correlation between the response and noradrenaline content. An intrathecal injection of phentolamine (α-adrenoceptor antagonist) enhanced serotonin-induced biting, although prazosin (α1-, α2B-, and α2C-adrenoceptor antagonist) and yohimbine (α2-adrenoceptor antagonist) had no effects. Intrathecal injections of phenylephrine (α1-adrenoceptor agonist) and clonidine (α2-adrenoceptor agonist) inhibited serotonin-induced biting. The action of phenylephrine was antagonized by intrathecal prazosin but not 5-methylurapidil (α1A-adrenoceptor antagonist), cyclazosin (α1B-adrenoceptor antagonist), and BMY 7378 (α1D-adrenoceptor antagonist). mRNAs encoding α1A-, α1B-, α2A-, α2B-, and α2C-adrenoceptor subtypes were expressed in the dorsal root ganglion and spinal dorsal horn. These results suggest that the descending noradrenergic system exerts tonic inhibition on itch signaling in the spinal cord. Both α1- and α2-adrenoceptors may be involved in the tonic inhibition of itch signaling and the stimulation of either α-adrenoceptor subtype may result in the inhibition of itch. [Copyright &y& Elsevier]

Abstract: Activation of coronary vascular α-adrenoceptors results in vasoconstriction which competes with metabolic vasodilation during sympathetic activation. Epicardial conduit vessel constriction is largely mediated by α1-adrenoceptors; the constriction of the resistive microcirculation largely by α2-adrenoceptors, but also by α1-adrenoceptors. There is no firm evidence that α-adrenergic coronary vasoconstriction exerts a beneficial effect on transmural blood flow distribution. In fact, α-blockade in anesthetized and conscious dogs improves blood flow to all transmural layers, during normoperfusion and hypoperfusion. Also, in patients with coronary artery disease, blockade of α1- and α2-adrenoceptors improves coronary blood flow, myocardial function and metabolism. [Copyright &y& Elsevier]

Diabetes is associated with an increased vascular tone usually involved in the pathogenesis of diabetic cardiovascular complications such as hypertension, stroke, coronary artery disease, or erectile dysfunction (ED). Enhanced contractility of penile erectile tissue has been associated with augmented activity of the RhoA/Rho kinase (RhoK) pathway in models of diabetes-associated ED. The present study assessed whether abnormal vasoconstriction in penile arteries from prediabetic obese Zucker rats (OZRs) is due to changes in the intracellular Ca2+ concentration ([Ca2+]i) and/or in myofilament Ca2+ sensitivity. Penile arteries from OZRs and lean Zucker rats (LZRs) were mounted on microvascular myographs for simultaneous measurements of [Ca2+]i and tension. The relationships between [Ca2+]i and contraction for the α1-adrenergic vasoconstrictor phenylephrine (PE) were left shifted and steeper in OZRs compared with LZRs, although the magnitude of the contraction was similar in both groups. In contrast, the vasoconstriction induced by the thromboxane A2 receptor agonist U-46619 was augmented in arteries from OZRs, and this increase was associated with an increase in both the sensitivity and maximum responses to Ca2+. The RhoK inhibitor Y-27632 (10 μM) reduced the vasoconstriction induced by PE to a greater extent in OZRs than in LZRs, without altering Ca2+. Y-27632 inhibited with a greater potency the contraction elicited by high KCl in arteries from OZRs compared with LZRs without changing [Ca2+]i. RhoK-II expression was augmented in arteries from OZRs. These results suggest receptor-specific changes in the Ca2+ handling of penile arteries under conditions of metabolic syndrome. Whereas augmented vasoconstriction upon activation of the thromboxane A2 receptor is coupled to enhanced Ca2+ entry, a RhoK-mediated enhancement of myofilament Ca2+ sensitivity is coupled with the α1-adrenergic vasoconstriction in penile arteries from OZRs. [ABSTRACT FROM AUTHOR]

P2X 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 receptor-regulated vasoconstriction in the different types of arteries in the rat is not clear as compared with α-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) was the same as that of maximal vasoconstrictions for noradrenaline ( E) in the internal carotid, pulmonary, mesenteric arteries, and aorta. Moreover, the value of ( E/ E)/( E/ E) was 0.4 in each of the four arteries, but it was 0.8 in the tail artery. In conclusion, P2X 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. [ABSTRACT FROM AUTHOR]

We investigated cardiac and vascular gene profiles in response to immobilization stress (IMO) in rats, an animal model of emotional stress-induced takotsubo cardiomyopathy using microarray analysis, followed by re-confirmation with real-time reverse transcription-polymerase chain reaction. Expression levels of the identified genes were further estimated by pretreatment with an α1-adrenoceptor blocker and/or a β1-adrenoceptor blocker. In response to IMO, expression of 46 genes was significantly altered in the heart and that of 49 genes was significantly altered in the aorta. Pathway analysis with DAVID Bioinformatics Resources indicated that regulation of transcription and response to endogenous stimulation were the top two scoring pathways. Altered expression of cardiac genes was blunted by pretreatment with a β1-adrenoceptor blocker or α1 + β1-adrenoceptor blockers. In contrast, that of aortic genes was blunted by pretreatment with an α1-adrenoceptor blocker or α1 + β1-adrenoceptor blockers. Activation of α1-adrenoceptor in the blood vessels or activation of β1-adrenoceptors in the heart were mainly responsible for emotional stress-induced alteration of cardiac and vascular gene profiles. [ABSTRACT FROM AUTHOR]

Purpose: Combination therapy of male lower urinary tract symptoms with α-adrenoceptor and muscarinic receptor antagonists attracts increasing interest. Propiverine is a muscarinic receptor antagonist possessing additional properties, i.e., block of L-type Ca channels. Here, we have investigated whether propiverine and its metabolites can additionally antagonize α-adrenoceptors. Methods: Human prostate and porcine trigone muscle strips were used to explore inhibition of α-adrenoceptor-mediated contractile responses. Chinese hamster ovary (CHO) cells expressing cloned human α-adrenoceptors were used to determine direct interactions with the receptor in radioligand binding and intracellular Ca elevation assays. Results: Propiverine concentration-dependently reversed contraction of human prostate pre-contracted with 10 μM phenylephrine (−log IC [M] 4.43 ± 0.08). Similar inhibition was observed in porcine trigone (−log IC 5.01 ± 0.05), and in additional experiments consisted mainly of reduced maximum phenylephrine responses. At concentrations ≥1 μM, the propiverine metabolite M-14 also relaxed phenylephrine pre-contracted trigone strips, whereas metabolites M-5 and M-6 were ineffective. In radioligand binding experiments, propiverine and M-14 exhibited similar affinity for the three α-adrenoceptor subtypes with −log K [M] values ranging from 4.72 to 4.94, whereas the M-5 and M-6 did not affect [H]-prazosin binding. In CHO cells, propiverine inhibited α-adrenoceptor-mediated Ca elevations with similar potency as radioligand binding, again mainly by reducing maximum responses. Conclusions: In contrast to other muscarinic receptor antagonists, propiverine exerts additional L-type Ca-channel blocking and α-adrenoceptor antagonist effects. It remains to be determined clinically, how these additional properties contribute to the clinical effects of propiverine, particularly in male voiding dysfunction. [ABSTRACT FROM AUTHOR]

The present study examined the ability of 6-fluoronorepinephrine (6FNE), a full selective α-adrenoceptor agonist, to produce antidepressant-like effects in mice. The drug, administered in the 4th ventricle, produced marked anti-immobility effects at mid-dose range in the acute forced swim, tail suspension and repeated open-space forced swim tests with minimal effect on open-field motor activity and also reversed anhedonia following lipopolysaccharide administration. Its antidepressant effects were equal to or greater than that of an established systemic antidepressant, desmethylimipramine, given subacutely. Experiments with α-adrenoceptor antagonists indicated that the drug acts primarily via the α2-receptor in contrast to endogenous catecholamines which appear to control depressive behaviour primarily via the α1-receptor. Antidepressant activity declined at higher doses signifying a possible pro-depressant effect of one of the α-adrenoceptor subtypes. Compared to the selective α2-agonist, dexmedetomidine, 6FNE showed equivalent antidepressant action in the tail suspension test but appeared to have a greater efficacy or speed of action in the repeated open-space forced swim test which produces a more sustained depression. Studies of regional brain Fos expression induced during the antidepressant tests showed that 6FNE tended to inhibit neural activity in two stress-responsive regions (locus coeruleus and paraventricular hypothalamus) but to enhance activity in two areas involved in motivated behaviour (nucleus accumbens shell and lateral septal nucleus) producing a neural pattern consistent with antidepressant action. It is concluded that 6FNE elicits a rapid and effective antidepressant and anti-stress response that may compare favourably with available antidepressants. [ABSTRACT FROM AUTHOR]

Electrical intercellular communication in the heart allows the propagation of an action potential from cell to cell. This is realized by low-ohmic cell-to-cell channels, the gap junction channels, which are dodecameric proteins consisting of two hexameric hemichannels. Each of the neighbouring cell provides one hemichannel, which consists of six connexins. In the heart, the connexin isoforms Cx43, Cx40 and Cx45 are present with Cx43 being the most abundant isoform. This intercellular communication is regulated acutely by control of the gap junction conductance and chronically by control of the connexin expression. The short half-life time of Cx43 indicates the permanent adaptation of cell communication to the actual requirements. β-Adrenoceptor stimulation enhances Cx40- but reduces Cx45-conductance, while Cx43 channels in most species do not seem to be acutely affected by β-adrenoceptor signalling. In contrast, chronic exposure to β-adrenergic stimulants activates protein kinase A and the mitogenic-activated protein kinase cascade (including protein 38 (p38), mitogenic-activated protein kinase kinase 1, extracellular signal-regulated kinase (ERK)1/2 and c-JUN NH terminal kinase (JNK)), the calcineurin pathway, translocation of activator protein 1 (AP1), CRE-binding protein and nuclear factor of activated T cells, finally leading to enhanced Cx43-mRNA and Cx43-protein expression together with Cx43 phosphorylation, but does not affect Cx40. α-Adrenoceptors also play a role in controlling cardiac intercellular communication: α-adrenergic stimulation acutely uncouples the cells, while a chronic stimulation enhances Cx43 expression via protein kinase C, p38, ERK1/2, JNK, c-fos and AP1, but does not alter Cx40 expression. While general cardiac protein synthesis, e.g. of β-actin, is controlled via α-adrenoceptors, Cx43 expression is regulated via α-adrenoceptors. However, α-adrenoceptor density in the heart varies among species, with high abundance in rat heart and low in human heart. Acute α-adrenergic stimulation, e.g. during ischemia, can lead to uncoupling and facilitates re-entrant arrhythmia. Chronic adrenergic upregulation of Cx43 expression seems to be involved in cardiac hypertrophy. In maladaptive hypertrophy, the enhanced Cx43 is increasingly incorporated in the lateral membrane of the cells rather at the cell poles, which may mean a gap junction disarray. This could-together with a mismatch in cell size and coupling-contribute to arrhythmogenesis. Thus, cardiac adrenoceptors are directly involved in the control of intercellular electrical communication and thus probably are a critical factor in the maintenance of regular cell-to-cell conduction and of the cardiac electrical networking. They probably are involved in the formation of an arrhythmogenic substrate in certain heart diseases. [ABSTRACT FROM AUTHOR]

Abstract: Zebrafish, like other teleosts, display rapid skin color change in response to the background through sympathetic nerves. Here, the α- and β-adrenoceptors of melanophores were studied pharmacologically both in zebrafish embryo and adult scale. In vitro experiments on adult scale melanophores demonstrated that both α1- and α2-adrenoceptors are functional in melanosome aggregation, the α2 subtype being predominant. Most melanophores in zebrafish embryos were able to concentrate melanosomes to α2-adrenergic agonist α-methylnorepinephrine when they first appeared. This ability increased at least in the following 48h, showing melanophores at these stages have developed functional adrenoceptors and these receptors increase independently before sympathetic innervation. However, even high concentration (10−3 M) of α1-adrenoceptor agonist phenylephrine was not able to evoke any paling of the embryos. In adult scales, propranolol enhanced the melanosome-aggregating response of epinephrine and isoproterenol, but not norepinephrine, indicating β-adrenoceptor mediates melanosome-dispersing response in adult zebrafish. Similar response was not observed in embryos until 60h post-fertilization (hpf). The melanophore adrenoceptor blocking effects of phentolamine and propranolol in embryos were much lower than that in adult zebrafish, suggesting these adrenoceptors in developing melanophores are less sensitive to the classical antagonists. [Copyright &y& Elsevier]

Abstract: In rat tail artery, short trains of electrical stimuli evoke both ATP-mediated excitatory junction potentials (EJPs) and a slow noradrenaline (NA)-mediated depolarization (NAD). Here we have investigated the contribution of α1- and α2-adrenoceptors to the NAD. The α1-adrenoceptor antagonist, prazosin (0.1μM), and the α2-antagonist, rauwolscine (1μM), reduced the amplitude of the NAD and in combination these agents virtually abolished the NAD. The KATP channel blocker, glibenclamide (10μM) abolished the α2-adrenoceptor-mediated component of the NAD, indicating that activation of these receptors produces closure of KATP channels. The α1-adrenoceptor-mediated component of the NAD was increased in amplitude by glibenclamide. Changes in membrane conductance were monitored by measuring the time constant of decay of EJPs (τEJP). The τEJP was increased during α1-adrenoceptor-mediated depolarization, indicating a decrease in membrane conductance; i.e. closure of K+ channels. Broad-spectrum K+ channel blockers (tetraethylammonium, 4-aminopyridine, Ba2+) and the TASK-1K+ channel blocker, anandamide (10μM), did not reduce the α1-adrenoceptor-mediated NAD. The α1-adrenoceptor-mediated NAD was unaffected by the Cl− channel blockers, 9-anthracene carboxylic acid (100μM) and niflumic acid (10μM) or by the non-selective cation channel blocker, SKF 96365 (10μM). These findings indicate that the NAD is produced by activation of both α1-and α2-adrenoceptors. The α2-adrenoceptor-mediated component is produced by closure of KATP channels whereas the α1-adrenoceptor-mediated component is most likely mediated by closure of another type of K+ channel. [Copyright &y& Elsevier]

Abstract: Noradrenaline, essential for the modulation of memory, is released in various parts of the brain from nerve terminals controlled by the locus coeruleus (LoC). Noradrenaline release consequent upon input from higher brain areas also occurs within the LoC itself. We examined the effect of noradrenaline on adrenergic receptors in the LoC on memory processing, using colored bead discrimination learning in the young domestic chick. We have shown previously that the release of noradrenaline in the hippocampus and cortex (mesopallium) is essential for acquisition and consolidation of short-term to intermediate and to long-term memory. Noradrenaline release within the LoC is triggered by the glutamatergic input from the forebrain. Inhibition by LoC injection of NMDA or AMPA receptor antagonists is rescued by injection of β2-and β3-adrenoceptor (AR) agonists in the hippocampus. We show that inhibition of α2A-ARs by BRL44408 in the LoC up to 30 min post-training consolidates weakly-reinforced learning. Conversely activation of α2A-ARs in the LoC at the times of consolidation between short-term and intermediate and long-term memory caused memory loss, which is likely to be due to a decreased release of noradrenaline within these two time windows. The α2A-AR antagonist will block presynaptic inhibitory receptors leading to an increase in extracellular noradrenaline. This interpretation is supported by the actions of noradrenaline uptake blockers that produce the same memory outcome. BRL44408 in the mesopallium also caused memory enhancement. β2-ARs are important in the first time window, whereas α1-, α2C-and β3-ARs are important in the second time window. The results reveal that for successful memory formation noradrenaline release is necessary within the LoC as well as in other brain regions, at the time of consolidation of memory from short-term to intermediate and from intermediate to long-term memory. [ABSTRACT FROM AUTHOR]

Abstract: Mesenteric veins are more sensitive than arteries to the constrictor effects of sympathetic nerve stimulation and α-adrenoceptor agonists. We tested the hypothesis that α1- and α2-adrenoceptors interact to enhance adrenergic reactivity of mesenteric veins. We studied neurogenic and agonist-induced constrictions of mesenteric veins and arteries in vitro. Norepinephrine concentration–response curves were left-shifted in veins compared to arteries. UK 14,304 (0.01–1μM, α2-adrenoceptor receptor agonist) did not constrict arteries or veins but enhanced constrictions and Ca2+ signals mediated by α1-adrenoceptor stimulation in veins. Yohimbine (α2-adrenoceptor receptor antagonist) and MK912 (α2C-adrenoceptor receptor antagonist), but not α2A- or α2B-adrenoceptor antagonists, produced rightward shifts in norepinephrine concentration–response curves in veins. Pharmacological studies revealed that α1D-adrenoceptors mediate venous constrictions. Norepinephrine responses in veins from α2C-adrenoceptor knock-out (KO) mice were not different from wild type veins. Yohimbine inhibited norepinephrine constrictions in α2C-adrenoceptor KO veins suggesting that there is upregulation of other α2-adrenoceptors in α2C-KO mice. These data indicate that α1D- and α2C-adrenoceptors interact in veins but not in arteries. This interaction enhances venous adrenergic reactivity. Mesenteric vein-specific α2-adrenoceptor linked Ca2+ and perhaps other signaling pathways account for enhanced venous adrenergic reactivity. [ABSTRACT FROM AUTHOR]

Abstract: Organic cation transporters (OCTs), comprising OCT1, OCT2 and OCT3 subtypes, control absorption and elimination of xenobiotics and endogenous compounds in kidney, liver and placenta. In addition, they ensure “uptake2”, low-affinity catecholamine clearance in sympathetically-innervated tissue and the CNS. The prototypical OCT ligand, disprocynium24 (D24), recognises OCT3, but its actions at OCT1 and OCT2 remain unknown. Herein, together with two other isocyanine derivatives (AAC291 and AAC301) and chemically-related adrenergic agents, we evaluated actions of D24 at OCTs, monoamine transporters and α1- and α2-adrenoceptors. D24 concentration-dependently suppressed [3H]-1-methyl-4-phenylpyridinium (MPP+) transport at human (h) and rat (r) OCT1, OCT2 and OCT3 in stably transfected HEK293 cells. Interestingly, low concentrations of D24 enhanced transport by h/rOCT2, a substrate-dependent effect suppressed by inhibition of protein kinase C. AAC291 and AAC301 likewise inhibited transport by all classes of h/r OCT and at low concentrations induced even more marked increases in transport by h/rOCT2. Further, by analogy to D24, they displayed antagonist properties at hα1A/B/D-adrenoceptors (Ca2+-flux) and hα2A/B/C-adrenoceptors ([35S]GTPγS binding). They were, however, less potent than D24 at serotonin transporters ([3H]citalopram binding) and AAC291 did not bind to dopamine and norepinephrine transporters. The preferential α1B-adrenoceptor antagonist, AH11110A, the α2-adrenoceptor agonist, RWJ52353, and the adrenergic neurotoxin DSP-4 likewise affected [3H]MPP+ transport, in an OCT-subtype and species-dependent manner. In conclusion, D24, other isocyanine congeners and chemically-related adrenergic agents inhibit OCT-mediated [3H]MPP+ transport, and all drugs display significant activity at α1- and α2-adrenoceptor subtypes, expanding previous reports of promiscuity between pharmacophores recognising α-adrenoceptors and OCTs. [Copyright &y& Elsevier]

The study examined the effect of α-adrenoceptor stimulation with methoxamine on chronotropic function of isolated heart perfused ex vivo according to Langendorff and cardiac chronotropy in vivo. Stimulation of α-adrenoceptors in isolated heart induced gradually developing bradycardia, which progressed during several minutes. Similar stimulation in vivo produced a short-term bradycardia probably terminated by the compensatory influences in the whole organism. Comparison of the data obtained in both experimental paradigms during α1-adrenoceptor stimulation revealed unidirectional changes in cardiac chronotropy characterized with time-related peculiarities. [ABSTRACT FROM AUTHOR]

Abstract: Using both immunocytochemical and flow cytometric analyses of rat peritoneal exudate cells constitutive expression of tyrosine hydroxylase and both β2- and α1- adrenoceptors on macrophages was revealed. Furthermore, according to the characteristic assemblage of tyrosine hydroxylase and adrenoceptor subtype expression different macrophage subsets were identified. In vitro treatment of macrophages with the non-selective α,β-adrenoceptor agonist arterenol and/or the β-adrenoceptor antagonist propranolol indicated that β-adrenoceptors potentiated nitric oxide (NO) production and suggested α-adrenoceptor-mediated suppression of hydrogen peroxide (H2O2) production. An increase in H2O2 production in the presence of the α1-adrenoceptor antagonist ebrantil provided support for this. Chronic propranolol treatment in vivo led to increased NO and H2O2 production by peritoneal macrophages. Furthermore, this treatment resulted in opposing effects on the expression of β2- and α1-adrenoceptors on peritoneal macrophages (a stimulatory effect on β2-adrenoceptors and a suppressive effect on α1-adrenoceptors). In conclusion, a subset of resident peritoneal macrophages synthesizes catecholamines, which may exert differential effects on H2O2 and NO production via distinct adrenoceptors. Finally, chronic propranolol treatment affected adrenoceptor expression on peritoneal macrophages and altered their capacity to generate NO and H2O2. [Copyright &y& Elsevier]