Use of recombinant human α2-adrenoceptors to characterize subtype selectivity of antagonist binding

Marjamäki, Anne; Luomala, Kirsti; Ala-Uotila, Sari; Scheinin, Mika

doi:10.1016/0922-4106(93)90034-7

Cited by 66 publications

(24 citation statements)

References 16 publications

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“…The K d for the high-affinity site detected in the lateral (lat) PB, was in the range of that described for the alpha2c-adrenoceptor subtype reported as 1.4 nM in a preparation of membranes from transfected cells (Marjamaki et al 1993), while the high-affinity site in the PBel (4.7 nM) may represent alpha2A-adrenoceptors whose K a for [3H]-RAUW has been reported to be 7.4 nM in membranes from transfected cells (MarjamS_ki et al 1993). The Ki-values for the competitors yohimbine and prazosin also indicate the presence of subtypes A and C when compared to Ki-values found by others (Marjam~iki et al 1993). However, the low-affinity binding sites detected in PBel and PBlat (Ka>15 nM) cannot be identified at present and might represent non-specific binding sites.…”

Section: Discussionmentioning

confidence: 85%

Distribution of alpha2-adrenergic binding sites in the parabrachial complex of the rat

Herbert

Flügge

1995

Anat Embryol

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The present study describes the distribution of alpha 2-adrenoceptors in the parabrachial and Kölliker-Fuse nucleus of the rat by employing the tritium-labeled alpha 2-receptor antagonist rauwolscine ([3H]-RAUW) as a ligand. The [3H]-RAUW binding was densitometrically quantified in five nuclei of the parabrachial (PB) complex in serial coronal sections. We found that cytoarchitectonically and anatomically distinct nuclei of the PB complex exhibit different numbers of [3H]-RAUW-binding sites. The largest number of binding sites was observed over the external lateral PB and caudally over the waist area of the PB. Lower numbers of binding sites were found in the remaining lateral PB nuclei, followed by the medial PB and the Kölliker-Fuse nucleus. In addition we disclosed that the internal lateral PB contains a very low number of binding sites while the external medial PB is marked by dense [3H]-RAUW binding. Also, the affinities of the binding sites differed between the PB areas. High affinities were observed in the external lateral PB, the remaining lateral PB nuclei and in the waist area of the PB, while the medial PB and the Kölliker-Fuse nucleus exhibited only low affinities for the ligand. Furthermore, saturation curves demonstrated non-linear profiles, indicating the presence of more than one population of binding sites in the PB nuclei for the radioligand. Our data demonstrate that the PB exhibits a distinct distribution of alpha 2-adrenergic binding sites. These correlate well with the cytoarchitectonically defined nuclei of the PB complex and with the pattern of ascending axons from the medial nucleus of the solitary tract and the area postrema terminating in the PB. Since a large number of these projection neurons utilize adrenaline or noradrenaline as their transmitters, we conclude that solitary-parabrachial neurotransmission to the forebrain is, at least in part, mediated via alpha 2-adrenoceptors.

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Section: Discussionmentioning

confidence: 85%

Distribution of alpha2-adrenergic binding sites in the parabrachial complex of the rat

Herbert

Flügge

1995

Anat Embryol

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“…Stable recombinant Shionogi 115 mouse mammary tumour cell lines (S115) expressing the human α 2A -, α 2B -or α 2C -adrenoceptor subtypes were used (Marjamäki et al 1993;Ala-Uotila et al 1994). The S115 cells were homogenized in 30 volumes of 50 mM Tris buffer with 5 mM EDTA (pH 7.5 at 4°C).…”

Section: Methodsmentioning

confidence: 99%

Evaluation of the effects of a specific α2-adrenoceptor antagonist, atipamezole, on α1- and α2-adrenoceptor subtype binding, brain neurochemistry and behaviour in comparison with yohimbine

Haapalinna

Viitamaa

MacDonald

et al. 1997

Naunyn-Schmiedeberg's Arch Pharmacol

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In the present study we evaluated the alpha 1- and alpha 2-adrenoceptor subtype binding, central alpha 2-adrenoceptor antagonist potency, as well as effects on brain neurochemistry and behavioural pharmacology of two alpha 2-adrenoceptor antagonists, atipamezole and yohimbine. Atipamezole had higher selectivity for alpha 2- vs. alpha 1-adrenoceptors than yohimbine regardless of the subtypes studied. Both compounds had comparable affinity for the alpha 2A-, alpha 2C- and alpha 2B-adrenoceptors, but yohimbine had significantly lower affinity for the alpha 2D-subtype. This may account for the fact that significantly higher doses of yohimbine than atipamezole were needed for reversal of alpha 2-agonist (medetomidine)-induced effects in rats (mydriasis) and mice (sedation and hypothermia). The effect on central monoaminergic activity was estimated by measuring the concentrations of transmitters and their main metabolites in whole brain homogenate. At equally effective alpha 2-antagonising doses in the rat mydriasis model, both drugs stimulated central noradrenaline turnover (as reflected by increase in metabolite levels) to the same extent. Atipamezole increased dopaminergic activity only slightly, whereas yohimbine elevated central dopamine but decreased central 5-hydroxytryptamine turnover rates. In behavioural tests, atipamezole (0.1-10 mg/kg) did not affect motor activity but stimulated food rewarded operant (FR-10) responding (0.03-3 mg/kg) whereas yohimbine both stimulated (1 mg/kg) and decreased (> or = 3 mg/kg) behaviour in a narrow dose range in these tests. In the staircase test, both antagonists increased neophobia, but in the two compartment test only yohimbine (> or = 3 mg/kg) decreased exploratory behaviour. The dissimilar effects of the antagonists on neurochemistry and behaviour are thought to be caused by non alpha 2-adrenoceptor properties of yohimbine. In conclusion, the alpha 2-antagonist atipamezole blocked all alpha 2-adrenoceptor subtypes at low doses, stimulated central noradrenergic activity and had only slight effects on behaviour under familiar conditions, but increased neophobia. The low affinity for the alpha 2D-adrenoceptor combined with its unspecific effects complicates the use of yohimbine as pharmacological tool to study alpha 2-adrenoceptor physiology and pharmacology.

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“…Atipamezole, a new potent and selective a2-adrenoceptor antagonist having similar affinities to all three x2-adrenoceptor subtypes (Harrison et al, 1991;Marjamaki et al, 1993), was used in the present study to investigate possible beneficial effects of 02-receptor antagonism in the treatment of genetic obesity. Theoretically, at least two possible mechanisms of action of atipamezole could be implemented.…”

Section: Epididymal and Intraperitoneal White Fatmentioning

confidence: 99%

Potentiation of the anti‐obesity effect of the selective β3‐adrenoceptor agonist BRL 35135 in obese Zucker rats by exercise

Santti

Huupponen

Rouru

et al. 1994

British J Pharmacology

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1 The effects of chronic treatments with a selective P3-adrenoceptor agonist and a selective a2-adrenoceptor antagonist and their interactions with physical exercise training were studied in experimental obesity.2 BRL 35135 (p3-agonist, 0.5 mg kg-' day-' p.o.), atipamezole (OE2-antagonist, 4.0 mg kg-' day-' p.o.) and placebo were given to genetically obese male Zucker rats. Half of the rats were kept sedentary whereas the other half were subjected to moderate treadmill exercise training. Body weight gain, cumulative food intake, the neuropeptide Y content of the hypothalamic paraventricular nucleus, brown adipose tissue thermogenic activity (measured as GDP binding), plasma insulin and glucose levels were measured after 3 weeks' treatment and exercise. 3 Treatment with BRL 35135 reduced weight gain by 19%, increased brown adipose tissue thermogenic activity 45-fold and reduced plasma insulin by 50%. Atipamezole slightly increased food intake and neuropeptide Y content in the paraventricular hypothalamic nucleus but had no effect on the other measured parameters. Exercise alone had no effect on weight gain, food intake or thermogenic activity, whereas it reduced plasma insulin and glucose levels. 4 The effect of BRL 35135 on weight gain and thermogenic activity was significantly potentiated by exercise; the reduction in weight gain was 56% in comparison with 19% in sedentary animals. Food intake was significantly reduced in the BRL 35135-treated-exercise-trained animals, although neither p3-agonist nor exercise alone affected it. 5 Based on the present results in genetically obese Zucker rats, combination of 03-agonist treatment with a moderate physical training may offer a new feasible approach to the therapy of obesity.-

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Use of recombinant human α2-adrenoceptors to characterize subtype selectivity of antagonist binding

Cited by 66 publications

References 16 publications

Distribution of alpha2-adrenergic binding sites in the parabrachial complex of the rat

Distribution of alpha2-adrenergic binding sites in the parabrachial complex of the rat

Evaluation of the effects of a specific α2-adrenoceptor antagonist, atipamezole, on α1- and α2-adrenoceptor subtype binding, brain neurochemistry and behaviour in comparison with yohimbine

Potentiation of the anti‐obesity effect of the selective β3‐adrenoceptor agonist BRL 35135 in obese Zucker rats by exercise

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