Biomedical subjects

Mika Scheinin

Publications and source records attributed to Mika Scheinin.

At least 37 records · Page 2Linked to original sources

PubMed2004

Human positron emission tomography studies of brain neurokinin 1 receptor occupancy by aprepitant.

BACKGROUND: Aprepitant is a highly selective substance P (neurokinin 1 [NK(1)] receptor) antagonist that significantly improves the pharmacotherapy of acute and delayed highly emetogenic chemotherapy-induced nausea and vomiting, probably through an action in the brain stem region of the central nervous system. Here, we report the use of positron emission tomography imaging with the NK(1) receptor binding-selective tracer [(18)F]SPA-RQC to determine the levels of central NK(1) receptor occupancy achieved by therapeutically relevant doses of aprepitant in healthy humans. METHODS: Two single-blind, randomized, placebo-controlled studies in healthy subjects were performed. The first study evaluated the plasma concentration-occupancy relationships for aprepitant dosed orally at 10, 30, 100, or 300 mg, or placebo (n = 12). The second study similarly evaluated oral aprepitant 30 mg and placebo (n = 4). In each study, dosing was once daily for 14 consecutive days. Data from both studies were combined for analyses. The ratio of striatal/cerebellar [(18)F]SPA-RQ (high receptor density region/reference region lacking receptors) was used to calculate trough receptor occupancy 24 hours after the last dose of aprepitant. RESULTS: Brain NK(1) receptor occupancy increased after oral aprepitant dosing in both a plasma concentration-related (r =.97; 95% confidence interval [CI] =.94-1.00, p <.001) and a dose-related (r =.94; 95% CI =.86-1.00, p <.001) fashion. High (> or =90%) receptor occupancy was achieved at doses of 100 mg/day or greater. The plasma concentrations of aprepitant that achieved 50% and 90% occupancy were estimated as approximately 10 ng/mL and approximately 100 ng/mL, respectively. CONCLUSIONS: Positron emission tomography imaging with [(18)F]SPA-RQ allows brain NK(1) receptor occupancy by aprepitant to be predicted from plasma drug concentrations and can be used to guide dose selection for clinical trials of NK(1) receptor antagonists in central therapeutic indications.

Adult↗

PubMed2004

Loss of amitriptyline analgesia in alpha 2A-adrenoceptor deficient mice.

Tricyclic antidepressants have analgesic and sedative effects in addition to their antidepressive properties. We tested the acute analgesic and locomotor inhibitory effects of the tricyclic antidepressant amitriptyline and the alpha(2)-adrenoceptor agonist clonidine in wild-type control and in alpha(2A)-adrenoceptor knockout mice in hot-plate and tail-flick tests. Amitriptyline-induced analgesia was lost in alpha(2A)-adrenoceptor knockout mice. The locomotor inhibitory effect of amitriptyline was reduced, but not fully abolished in alpha(2A)-adrenoceptor knockout mice. Similar results were obtained with clonidine. We conclude that alpha(2A)-adrenoceptors appear to have a significant role in amitriptyline-induced acute analgesia in mice, and that alpha(2A)-adrenoceptors also participate in the sedative effects of amitriptyline.

Amitriptyline↗

PubMed2004

Cloning, characterisation and identification of several polymorphisms in the promoter region of the human alpha2B-adrenergic receptor gene.

Screening of a foetal brain genomic DNA library allowed to isolate a 10-kb fragment of the gene encoding the human alpha2B-adrenergic receptor, that contained 5.5 kb of the 5'-flanking region, the open reading frame and 2.9 kb of the 3'-flanking region. The 1-kb fragment upstream from the start codon was rich in GC, lacked consensus TATA or CAAT box, but contained several Sp1-binding sites. Other potential cis-regulatory elements found in the 5'-flanking region included AP2, USF, Stat-6, NFkappaB and Olf-1. A single canonical polyadenylation signal (AATAAA) was found at position +3252/+3257 and the polyadenylation site was 3274 nucleotides downstream from ATG. Transfection experiments with chimeric luciferase constructs containing various truncated fragments of the 5'-region showed that the fragment -3160/+3 exhibited promoter activity in all tested cell lines and permitted the definition of a minimal 200-bp promoter (-603/-411) containing three putative Sp1-binding sites and two initiator elements. Transcriptional activity of this region was inhibited by the addition of mithramycin, a specific inhibitor of Sp1 binding to GC-rich sequences. The search for sequence variants within a fragment covering 1.7 kb of 5'-flanking region and the coding region allowed us to identify five novel single nucleotide polymorphisms. Interestingly, the G/C substitution at position -98 relative to the start codon was common and in complete linkage with a previously identified insertion/deletion polymorphism in the coding region which was showed to affect alpha2B-adrenergic receptor function. Based on transfection data and computer-assisted sequence analysis, the -98 G/C single nucleotide polymorphism was located within a portion of the 5'-UTR (-127/+3) affecting luciferase activity and it created additional putative binding site for Sp1. However, G/C substitution had no significant incidence on promoter activity in BHK-21 or HeLa cells.

Base Sequence↗

PubMed2004

Clinical and pharmacological significance of alpha2-adrenoceptor polymorphisms in cardiovascular diseases.

The alpha2-adrenoceptors (alpha2-ARs) are receptors for endogenous catecholamines (norepinephrine and epinephrine) that mediate a number of physiological and pharmacological responses such as hypotension and sedation. Three distinct subtypes, denoted alpha2A-, alpha2B- and alpha2C-AR, have been characterized and cloned. Employment of mutation screening in the study of human populations from various ethnic backgrounds has shown that alpha2-AR genes are polymorphic. The functional and biochemical consequences of these polymorphisms have been analyzed by expressing the wild-type receptors and their respective genetic variants in heterologous systems such as CHO and COS-7 cells. Changes include alteration in G-protein coupling and in agonist-promoted receptor phosphorylation and desensitization. Case-control and population-based studies have shown clinical association with cardiovascular risk. Further investigation of the genetic variants in specialized cells and transgenic animals will provide the molecular basis of cardiovascular disease and may reveal alpha2-AR variants as potential targets for selective pharmacological interventions.

Cardiovascular Diseases↗

PubMed2004

Alpha2A-adrenoceptors are important modulators of the effects of D-amphetamine on startle reactivity and brain monoamines.

Amphetamines are commonly used to treat attention-deficit hyperactivity disorder, but are also widely abused. They are employed in schizophrenia-related animal models as they disrupt the prepulse inhibition (PPI) of the acoustic startle response. The behavioral effects of amphetamines have mainly been attributed to changes in dopamine transmission, but they also involve increases in the synaptic concentrations of norepinephrine (NE). alpha2-Adrenoceptors (alpha2-ARs) regulate the excitability and transmitter release of brain monoaminergic neurons mainly as inhibitory presynaptic auto- and heteroreceptors. Modulation of acoustic startle and its PPI by the alpha2A-AR subtype was investigated with mice lacking the alpha2A-AR (alpha2A-KO) and their wild-type (WT) controls, without drugs and after administration of the alpha2-AR agonist dexmedetomidine or the antagonist atipamezole. The interaction of D-amphetamine (D-amph) and the alpha2-AR-noradrenergic neuronal system in modulating startle reactivity and in regulating brain monoamine metabolism was assessed as the behavioral and neurochemical responses to D-amph alone, or to the combination of D-amph and dexmedetomidine or atipamezole. alpha2A-KO mice were supersensitive to both neurochemical and behavioral effects of D-amph. Brain NE stores of alpha2A-KO mice were depleted by D-amph, revealing the alpha2A-AR as essential in modulating the actions of D-amph. Also, increased startle responses and more pronounced disruption of PPI were noted in D-amph-treated alpha2A-KO mice. alpha2A-AR also appeared to be responsible for the startle-modulating effects of alpha2-AR drugs, since the startle attenuation after the alpha2-AR agonist dexmedetomidine was absent in alpha2A-KO mice, and the alpha2-AR antagonist atipamezole had opposite effects on the startle reflex in alpha2A-KO and WT mice.

Acoustic Stimulation↗

PubMed2004

Alpha(2A) adrenoceptors contribute to feedback inhibition of capsaicin-induced hyperalgesia.

BACKGROUND: Studies on receptor knockout mice have so far shown that of the three alpha2-adrenoceptor subtypes, the alpha(2A) adrenoceptor has a major role in mediating the powerful central analgesia induced by synthetic alpha2-adrenoceptor agonists. However, because a knockout of the gene for the alpha(2A) adrenoceptor has produced only little if any change in the pain sensitivity of control, nerve-injured, or inflamed animals, it has not been clear whether activation of alpha(2A)-adrenoceptors by endogenous ligands has a significant pain regulatory role. METHODS: The authors assessed spontaneous pain behavior and mechanical hypersensitivity induced by administration of capsaicin in the colon or paw of alpha(2A)-adrenoceptor knockout mice versus their wild-type controls. RESULTS: Enhanced pain hypersensitivity was observed in alpha(2A)-adrenoceptor knockout mice 20 min or more after administration of capsaicin, but before, hypersensitivity and spontaneous pain were of equal magnitude in alpha(2A)-adrenoceptor knockout and wild-type mice. When wild-type mice were pretreated with an alpha2-adrenoceptor antagonist, capsaicin-induced pain hypersensitivity increased to a level equal to that in alpha(2A)-adrenoceptor knockout mice. Capsaicin-induced hypersensitivity was suppressed in wild-type but not alpha(2A)-adrenoceptor knockout mice by a centrally acting alpha2-adrenoceptor agonist, whereas a peripherally acting alpha2-adrenoceptor agonist was without effect on hypersensitivity, although it attenuated capsaicin-induced spontaneous pain behavior in wild-type mice. CONCLUSIONS: This study shows that central alpha(2A)-adrenoceptors contribute to feedback inhibition of pain hypersensitivity. Also, alpha(2A)-adrenoceptors are critical for not only somatic but also visceral antinociceptive effects induced by synthetic alpha2-adrenoceptor agonists.

Administration, Rectal↗

PubMed2004

Neurochemical and behavioural changes in zebrafish Danio rerio after systemic administration of 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

Dopaminergic deficiency in the brain of zebrafish was produced by systemic administration of two catecholaminergic neurotoxins, 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the neurochemical and behavioural changes were characterized. The levels of dopamine and noradrenaline decreased significantly after the injection of MPTP and 6-OHDA. Corresponding to these changes, fish exhibited characteristic changes in locomotor behaviour, i.e. the total distance moved and velocity decreased after both neurotoxins. Tyrosine hydroxylase and caspase 3 protein levels were not altered after MPTP or 6-OHDA injections, as studied by immunohistochemistry and western blotting. The catecholaminergic cell clusters suggested to correspond to the mammalian nigrostriatal cell group displayed normal tyrosine hydroxylase immunoreactivity after the toxin treatment and did not show signs of DNA fragmentation that would indicate activation of cascades that lead to cell death. The results show that single systemic injections of MPTP and 6-OHDA induce both biochemical and behavioural changes in zebrafish, albeit failing to produce any significant morphological alteration in catecholaminergic cell clusters at the tested doses. This approach may be used for the screening of chemicals affecting the dopaminergic system. The model may be especially useful for evaluation of the role of novel genes in neurotoxicity, as a large number of zebrafish mutants are becoming available.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2003

The insertion/deletion variation in the alpha2B-adrenoceptor does not seem to modify the risk for acute myocardial infarction, but may modify the risk for hypertension in sib-pairs from families with type 2 diabetes.

BACKGROUND: An insertion/deletion polymorphism in the alpha2B-adrenoceptor (AR) has been associated with the risk for acute myocardial infarction (AMI) and sudden cardiac death. In this study we tested whether this polymorphism is associated with the risk for AMI among members of families with type 2 diabetes. METHODS: 154 subjects with a history of AMI were matched for age and sex with one of their siblings who did not have a history of AMI. The prevalence of the genotypes of the alpha2B-AR insertion/deletion polymorphism was compared between the siblings using McNemar's test. We also explored the data to see whether this genetic variation affects the risk for hypertension by using logistic regression models in the two subpopulations of subjects, with and without a history of AMI. RESULTS: Among all study subjects, 73 (24%) carried the alpha2B-AR deletion/deletion genotype, 103 (33%) carried the insertion/insertion genotype, and 132 (43%) were heterozygous. The distribution of genotypes of the alpha2B-AR insertion/deletion variation in the group of subjects with a history of AMI and their phenotype-discordant siblings did not statistically significantly differ from that expected by random distribution (p = 0.52): the deletion/deletion genotype was carried by 34 subjects with AMI (22%), and by 39 subjects without AMI (25%). Neither did we observe any significant difference in deletion allele frequencies of the alpha2B-AR insertion/deletion polymorphism between patients with a history of AMI (0.44) and their sib-pair controls (0.46, p = 0.65). In an exploratory analysis, the alpha2B-AR deletion/deletion genotype was associated with increased odds for hypertension compared with subjects carrying any of the other genotypes. CONCLUSIONS: The deletion/deletion genotype of the alpha2B-AR does not emerge in this study as a risk factor for AMI among members of families with type 2 diabetes; however, it might be involved in the development of hypertension.

Journal Article↗

PubMed2003

Identification of duplicated fourth alpha2-adrenergic receptor subtype by cloning and mapping of five receptor genes in zebrafish.

The alpha(2)-adrenergic receptors (alpha(2)-ARs) belong to the large family of rhodopsinlike G-protein-coupled receptors that share a common structure of seven transmembrane (TM) alpha-helices. The aims of this study were (1) to determine the number of alpha(2)-AR genes in a teleost fish, the zebrafish (Danio rerio), (2) to study the gene duplication events that generated the alpha(2)-AR subtypes, and (3) to study changes in receptor structure that have occurred since the divergence of the mammalian and fish lineages. Here, we report the cloning and chromosomal mapping of fish orthologs for all three mammalian alpha(2)-ARs. In addition, we identified a fourth alpha(2)-AR subtype with two duplicates in zebrafish. Chromosomal mapping showed that the zebrafish alpha(2)-AR genes are located within conserved chromosomal segments, consistent with the origin of the four alpha(2)-AR subtypes by two rounds of chromosome or block duplication before the divergence of the ray fin fish and tetrapod lineages. Thus, the fourth subtype has apparently been present in the common ancestor of vertebrates but has been deleted or is yet to be identified in mammals. The overall percentage identity between the fish and mammalian orthologs is 53% to 67%, and in the TM regions 80% to 87%. These values are clearly lower than what is observed between mammalian orthologs. Still, all of the residues thought to be important for alpha(2)-adrenergic ligand binding are conserved across species and subtypes, and even the most divergent regions of the fish receptors show clear "molecular fingerprints" typical for orthologs of a given subtype.

Animals↗

PubMed2003

Molecular mechanisms of ligand-receptor interactions in transmembrane domain V of the alpha2A-adrenoceptor.

1. The structural determinants of catechol hydroxyl interactions with adrenergic receptors were examined using 12 alpha2-adrenergic agonists and a panel of mutated human alpha2A-adrenoceptors. The alpha2ASer201 mutant had a Cys --> Ser201 (position 5.43) amino-acid substitution, and alpha2ASer201Cys200 and alpha2ASer201Cys204 had Ser --> Cys200 (5.42) and Ser --> Cys204 (5.46) substitutions, respectively, in addition to the Cys --> Ser201 substitution. 2. Automated docking methods were used to predict the receptor interactions of the ligands. Radioligand-binding assays and functional [35S]GTPgammaS-binding assays were performed using transfected Chinese hamster ovary cells to experimentally corroborate the predicted binding modes. 3. The hydroxyl groups of phenethylamines were found to have different effects on ligand affinity towards the activated and resting forms of the wild-type alpha2A-adrenoceptor. Substitution of Ser200 or Ser204 with cysteine caused a deterioration in the capability of catecholamines to activate the alpha2A-adrenoceptor. The findings indicate that (i) Cys201 plays a significant role in the binding of catecholamine ligands and UK14,304 (for the latter, by a hydrophobic interaction), but Cys201 is not essential for receptor activation; (ii) Ser200 interacts with the meta-hydroxyl group of phenethylamine ligands, affecting both catecholamine binding and receptor activation; while (iii) substituting Ser204 with a cysteine interferes both with the binding of catecholamine ligands and with receptor activation, due to an interaction between Ser204 and the para-hydroxyl group of the catecholic ring.

Adrenergic Agonists↗

PubMed2003

alpha 2B-Adrenoceptor levels govern agonist and inverse agonist responses in PC12 cells.

Receptor density is an important determinant of cellular effector responses to receptor activation. We analysed cytosolic Ca(2+) responses to alpha(2)-adrenergic agents in PC12 cells expressing human alpha(2B)-adrenergic receptors (AR) at two densities (3.8 and 1.3 pmol/mg protein). The efficacy (E(max)) of agonists was greater in cells with higher receptor expression; while the potency (EC(50)) of norepinephrine and oxymetazoline was independent of alpha(2B)-AR levels. Several classical alpha(2)-AR antagonists behaved as either partial or inverse agonists in a receptor density-dependent fashion. No apparent structural similarities were found among the inverse agonists, precluding simple predictions of inverse agonist activity. Transfected PC12 cells expressing alpha(2B)-AR at relatively high density would be a useful approach to screen inverse agonists for this class of receptors. Our results further indicate that receptor density significantly influences the properties of ligands, not only of partial agonists as predicted by classical receptor theory, but also of antagonists and full agonists.

Adrenergic alpha-2 Receptor Agonists↗

PubMed2003

Constitutive precoupling to G(i) and increased agonist potency in the alpha(2B)-adrenoceptor.

The human alpha(2B)-adrenoceptor (alpha(2B)-AR) was mutated by substituting the D(3.49) aspartate in position 109 with an alanine (alpha(2B)-D109A) in the conserved DRY sequence at the cytoplasmic face of TM3. We studied the effects of the mutation on agonist binding and on receptor activation in CHO cells, including possible inverse agonism monitored by measuring intracellular Ca(2+) concentrations ([Ca(2+)](i)). The mutated receptor had increased binding affinity for agonists, especially dexmedetomidine (3.8-fold). The increased affinity was abolished by pretreatment of the cells with pertussis toxin. The mutation produced constitutive receptor activity evidenced as increased basal [Ca(2+)](i) and increased potency and efficacy of agonists to elicit Ca(2+) responses. The imidazoline derivative RX821002 functioned as an inverse agonist only through the alpha(2B)-D109A, reducing [Ca(2+)](i). The results thus indicate that this mutation causes constitutive receptor-G(i)-protein precoupling, and that the D(3.49) aspartate residue of the DRY motif is involved in controlling coupled and uncoupled conformations of alpha(2B)-AR.

Adrenergic alpha-Antagonists↗

PubMed2003

The alpha2A-adrenoceptor subtype is not involved in inflammatory hyperalgesia or morphine-induced antinociception.

The purpose of the present study was to investigate the role of the alpha(2A)-adrenoceptor subtype in inflammatory hyperalgesia, and in adrenergic-mu-opioid interactions in acute pain and inflammatory hyperalgesia. Behavioral responses to mechanical and thermal stimuli were studied in alpha(2A)-adrenoceptor knockout mice and their wild-type controls. Thermal nociception was evaluated as paw withdrawal latencies to radiant heat applied to the hindpaws. Mechanical nociception was measured using von Frey monofilament applications to the hindpaws. Mechanical and thermal hyperalgesia, induced with intraplantar carrageenan (1 mg/40 microl) were compared in alpha(2A)-adrenoceptor knockout and wild-type mice. The effects of the systemically administered mu-opioid receptor agonist morphine (1-10 mg/kg) were evaluated on mechanical withdrawal responses under normal and inflammatory conditions in knockout and wild-type mice. Withdrawal responses to radiant heat and von Frey monofilaments were similar in alpha(2A)-adrenoceptor knockout and wild-type mice before and after the carrageenan-induced hindpaw inflammation. Also, the antinociceptive effects of morphine in mechanical nociceptive tests were similar before and after carrageenan-induced hindpaw inflammation. Our observations indicate that alpha(2A)-adrenoceptors are not tonically involved in the modulation of inflammation-induced mechanical and thermal hyperalgesia. In addition, alpha(2A)-adrenoceptors do not appear to play an important role in mu-opioid receptor-mediated antinociception or antihyperalgesia.

Analgesia↗

PubMed2003

The alpha2-adrenoceptor antagonist atipamezole reduces the development and expression of d-amphetamine-induced behavioural sensitization.

The possible effect of atipamezole, a potent and specific alpha(2)-adrenoceptor antagonist, on the development and expression of d-amphetamine-induced behavioural sensitization was evaluated in mice. Male (C57Bl/6J) mice were given daily doses of d-amphetamine (2 mg/kg). In addition, groups of mice received injections of atipamezole (0.3 or 1 mg/kg) 20 min before d-amphetamine or vehicle administration. Idazoxan (1 mg/kg) was used in some experiments to extend the results to other alpha(2)-adrenoceptor antagonists. Challenge doses of d-amphetamine were administered to the mice on days 7-9 to evaluate the effects of alpha(2)-adrenoceptor antagonists on the d-amphetamine sensitization, evidenced by increased locomotor activation. Mice treated repeatedly with d-amphetamine developed strong locomotor sensitization that was reduced by pretreatment with alpha(2)-adrenoceptor antagonists. Acute atipamezole at both doses attenuated the expression of d-amphetamine-induced sensitization. Atipamezole at 1 mg/kg alone had no effect on locomotor activity, but the lower dose (0.3 mg/kg) increased locomotor activity after repeated administration. These results indicate that alpha(2)-adrenoceptor antagonists modulate the actions of d-amphetamine in a manner not explicable by their enhancing actions on noradrenaline and dopamine release, and may thus provide a novel approach to the treatment of motor complications caused by dopaminergic agents, such as dyskinesias, and perhaps also drug dependence.

Adrenergic alpha-2 Receptor Antagonists↗

PubMed2003

Influence of prazosin and clonidine on morphine analgesia, tolerance and withdrawal in mice.

Rapid development of tolerance and dependence limits the usefulness of morphine in long-term treatment. We examined the effects of clonidine (alpha(2)-adrenoceptor agonist) and prazosin (alpha(1)-adrenoceptor antagonist) on morphine analgesia, tolerance and withdrawal. Morphine tolerance was induced using a 3-day cumulative twice-daily dosing regimen with s.c. doses up to 120 mg/kg. Tolerance was assessed on day 4, as loss of the antinociceptive effect of a test dose of morphine (5 mg/kg). After 10 h, morphine withdrawal was precipitated with naloxone (1 mg/kg). Prazosin had no analgesic effect alone but dose-dependently potentiated morphine analgesia in morphine-naive mice. Another alpha(1)-adrenoceptor antagonist, corynanthine, had similar effects. Prazosin also increased the analgesic potency of the morphine test dose in morphine-tolerant mice. Naloxone-precipitated vertical jumping was not affected, but weight loss was reduced by prazosin. Acutely administered clonidine potentiated morphine analgesia and alleviated opioid withdrawal signs, as expected. We conclude that in addition to the already established involvement of alpha(2)-adrenoceptors in opioid actions, also alpha(1)-adrenoceptors have significant modulatory role in opioid analgesia and withdrawal.

Adrenergic alpha-Agonists↗

PubMed2003

Variation in the alpha2B-adrenoceptor gene as a risk factor for prehospital fatal myocardial infarction and sudden cardiac death.

OBJECTIVES: Our aim was to corroborate the observed association between the deletion/deletion (DD) genotype of the insertion/deletion polymorphism in the alpha(2B)-adrenoceptor (AR) and increased risk for acute myocardial infarction (AMI), and to study whether this genotype also confers an increased risk for sudden cardiac death (SCD). BACKGROUND: Vasospasm has been suggested to play a role in AMI. Alpha(2)-AR mediate coronary vasoconstriction in humans, and studies on mice suggest the involvement of the alpha(2)-AR subtype B in vasoconstriction. A deletion variant of the human alpha(2B)-AR has been associated with impaired receptor desensitization in vitro. In a population-based prospective study of 912 middle-aged men, the DD genotype of the alpha(2B)-AR conferred an increased risk for AMI. METHODS: A series of 700 unselected sudden out-of-hospital deaths of middle-aged white men subjected to medico-legal autopsy was analyzed. RESULTS: Genotype information was obtained for 683 men (DD = 22%, insertion/deletion = 51%, insertion/insertion = 27%). Carriers of the DD genotype had an increased risk for SCD (n = 278, odds ratio [OR] = 2.0, p = 0.01) and fatal AMI (n = 84, OR = 2.1, p = 0.04) compared with the other two genotypes combined. The risks for SCD and fatal AMI were higher in carriers of the DD genotype who died before the age of 55 years (OR = 4.5 and 5.0, p < 0.001 for both). CONCLUSIONS: Middle-aged white men carrying the DD genotype of the alpha(2B)-AR have a significantly increased risk for SCD and AMI, especially before the age of 55 years.

Adult↗

PubMed2003

Functional expression and direct visualization of the human alpha 2B -adrenergic receptor and alpha 2B -AR-green fluorescent fusion protein in mammalian cell using Semliki Forest virus vectors.

The alpha 2B -adrenergic receptor ( alpha 2B -AR), a member of the G protein-coupled receptor (GPCR) superfamily, was expressed at high levels from Semliki Forest virus (SFV) vectors in mammalian cells. Constructs were engineered by fusing enhanced green fluorescent protein (eGFP) and the SFV capsid to opposite ends of the alpha 2B -AR. The receptor fusions alpha 2B -AR-eGFP and CAP- alpha 2B -AR expressed in CHO-K1 cells generated alpha 2B values of 176 and 122pmol/mg of membrane protein, respectively, and showed similar ligand binding characteristics, alpha 2B -AR subtype-selectivity, and G protein activation as reported for stable expression in CHO-K1 cells. Cryo-electron microscopy and eGFP-based fluorescence indicated the same subcellular receptor distribution. SFV expression is well suited for studies on the pharmacology, biochemistry, and cell biology of GPCRs, and for large-scale recombinant protein production in mammalian suspension culture to generate sufficient receptor quantities for structural biology.

Adrenergic alpha-2 Receptor Antagonists↗

PubMed2003

Alpha2-adrenergic drug effects on brain monoamines, locomotion, and body temperature are largely abolished in mice lacking the alpha2A-adrenoceptor subtype.

alpha(2)-ARs regulate brain monoaminergic function by inhibiting neuronal firing and release of monoamine neurotransmitters, noradrenaline (NA), serotonin (5-HT) and dopamine (DA). Both alpha(2A)- and alpha(2C)-AR inhibit monoamine release in vitro in brain slices, but the in vivo roles of individual alpha(2)-AR subtypes in modulating monoamine metabolism have not been characterised. Metabolism of brain monoamine neurotransmitters, locomotor activity and body temperature were investigated in mice with targeted inactivation of the gene encoding alpha(2A)-AR (alpha(2A)-knockout, alpha(2A)-KO) and wild-type (WT) mice after treatment with the alpha(2)-AR agonist dexmedetomidine and the antagonist atipamezole. Dexmedetomidine caused profound hypothermia (up to 14.7 degrees C mean reduction in rectal temperature) and locomotor inhibition in WT mice, and inhibited the turnover of NA, 5-HT and DA, but increased NA turnover in alpha(2A)-KO mice. alpha(2)-AR agonist-induced hypothermia and locomotor inhibition were attenuated, but not totally abolished, in alpha(2A)-KO mice. These results suggest that alpha(2A)-ARs are principally responsible for the alpha(2)-AR mediated inhibition of brain monoamine metabolism, but other alpha(2)-ARs, possibly alpha(2C)-ARs, are also involved, especially in the striatum. However, secondary effects of the physiological alterations caused by drug administration, especially hypothermia, may have contributed to the observed neurochemical changes in WT mice.

Adrenergic alpha-Agonists↗