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  • 1
    Electronic Resource
    Electronic Resource
    Effects of indomethacin on muscarinic inhibition of endogenous noradrenaline release from rat isolated trachea (1993)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 348 (1993), S. 21-27 
    Details
    ISSN: 1432-1912
    Keywords: Airways ; Methoctramine ; Muscarine receptors ; Noradrenaline release ; Prostanoids ; Indomethacin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The release of endogenous noradrenaline from rat isolated tracheae was evoked by electrical field stimulation (3 Hz, 540 pulses) in the presence of yohimbine, desipramine and tyrosine. The muscarine receptor agonist oxotremorine concentration-dependently inhibited the evoked release of noradrenaline by 95% at 1 μmol/l, EC50 values in two series of experiments 41 and 57 nmol/l, respectively. The effect of oxotremorine was antagonized by the non-selective muscarine receptor antagonist scopolamine (10–1000 nmol/l) in a manner suggesting a simple competitive interaction (slope of Schild plot −0.94; pA2 value 8.88). However, the M2 selective muscarine receptor antagonist methoctramine (0.1–10 μmol/l) affected the action of oxotremorine in a manner suggesting a complex interaction (slope of Schild plot −0.47). Addition of indomethacin (3 μmol/l) caused an increase of the evoked release of noradrenaline by 45% and low concentrations of oxotremorine (0.01 and 0.1 μmol/l, but not 1 μmol/l) became less effective resulting in a slight shift to the right of the concentration response curve (EC50 169 nmol/l). Moreover, in the presence of indomethacin methoctramine (0.1–10 μmol/l) antagonized the effects of oxotremorine in a manner suggesting a simple competitive interaction (slope of Schild plot −0.93, pA2 value 7.61). In the presence of indomethacin, the concentration response curve of oxotremorine was only slightly shifted to the right in the presence of the M1 receptor selective antagonist pirenzepine (1 μmol/l, −log KB 6.1) and not significantly affected by the M3 receptor selective antagonist pfluoro-hexahydrosiladifenidol (1 μmol/l). In conclusion, the release of noradrenaline in the rat trachea is inhibited via presynaptic muscarine heteroreceptors of the M2 subtype. In addition, activation of muscarine receptors affects the release of noradrenaline also indirectly, probably via the release of inhibitory prostanoids, and this involves muscarine receptors which are pharmacologically different from those at the sympathetic nerve terminals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168532
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  • 2
    Electronic Resource
    Electronic Resource
    β Adrenoceptor-mediated facilitation of endogenous noradrenaline release from rat isolated trachea (1994)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 350 (1994), S. 459-463 
    Details
    ISSN: 1432-1912
    Keywords: Airways ; β-Adrenoceptors ; Noradrenaline release ; Formoterol ; Epithelium ; Mucosa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Overflow of endogenous noradrenaline from rat isolated tracheae was evoked by electrical field stimulation (3 Hz, 540 pulses) in the presence of yohimbine, desipramine and tyrosine. Isoprenaline 100 nmol/l increased the evoked overflow of noradrenaline by about 65%. This effect was antagonized by propranolol (100 nmol/l) and the β2-selective adrenoceptor antagonist ICI 118,551 (100 nmol/l), but not by the β1-selective adrenoceptor antagonist CGP 20712 A (100 nmol/l). The β2-selective adrenoceptor agonist formoterol (1–100 nmol/l) also facilitated the evoked overflow of noradrenaline, but maximally by only about 25% at 10 nmol/l, i.e. formoterol behaved as a partial agonist at these facilitatory β-adrenoceptor. This assumption is also supported by the observation that formoterol (10 nmol/l) acted as antagonist against isoprenaline (100 nmol/l). Mechanical removal of the mucosa resulted in a 30% decrease in tissue noradrenaline and a 55% reduction of the evoked overflow of noradrenaline. In mucosa-denuded preparations isoprenaline failed to facilitate noradrenaline overflow. In the presence of indomethacin (3 μmol/l) the evoked overflow of noradrenaline from mucosa containing preparations was increased by about 50%, but isoprenaline still further facilitated the evoked noradrenaline overflow by about 40%. In conclusion, the overflow of noradrenaline in the rat trachea is facilitated via β2-adrenoceptors, an effect which requires an intact air-way mucosa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00173014
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  • 3
    Electronic Resource
    Electronic Resource
    Muscarinic inhibition of endogenous noradrenaline release from rabbit isolated trachea: receptor subtype and receptor reserve (1994)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 350 (1994), S. 464-472 
    Details
    ISSN: 1432-1912
    Keywords: Airways ; Rabbit trachea ; Noradrenaline release ; Muscarine receptors ; M2 muscarine receptor subtype ; Prejunctional receptors ; Oxotremorine dissociation constant ; Receptor reserve
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of the present study was to characterize putative muscarine receptors on sympathetic nerve terminals in the rabbit trachea. Release of endogenous noradrenaline from in vitro incubated rabbit tracheae was evoked by electrical field stimulation (3 Hz, 540 pulses) and quantified by high performance liquid chromatography with electrochemical detection. The muscarine receptor agonist oxotremorine inhibited the evoked release of noradrenaline completely at 1 μol/l (EC50: 64 nmol/l). The concentration response curve was very steep (Hill coefficient of 2.3). Scopolamine shifted the concentration response curve of oxotremorine to the right (−log KB 8.48) demonstrating specific, inhibitory muscarine receptors. Several subtype-preferring muscarine receptor antagonists also shifted the concentration response curve of oxotremorine to the right. The rank order of potency was (−log KB or pA* 2): scopolamine (8.48) 〉 AF DX 384 (7.88*; slope of Schild plot 1.1) 〉 (R)-trihexyphenidyl (7.87) 〉 4-DAMP (7.85) 〉 AQ-RA 741 (7.77) ≫ methoctramine 6.18 〉 pirenzepine (6.0) 〉p-fluoro-hexahydrosiladifenidol (p-FHHSiD, 5.68). When these affinity constants were plotted against reported −log Ki values determined in binding studies on human cloned muscarine receptor subtypes (m1-m5), the best correlation was obtained for m2. Indomethacin (3 μmol/l), which on its own increased the evoked noradrenaline release by about 45%, affected neither the inhibitory effect of oxotremorine nor the antagonistic potency of methoctramine or p-FHHSiD. After preincubation for 48 min with 300 μmol/l phenoxybenzamine, which has been shown to inactivate muscarine receptors irreversibly, the concentration response curve of oxotremorine was shifted 5.2 fold to the right and the maximal inhibition was reduced by 50%, whereas the slope remained steep (Hill coefficient 2.6). These experiments indicated that a fraction of about 22% of the muscarine receptors has to be occupied by oxotremorine to produce half-maximum inhibition of noradrenaline release; the dissociation constant of oxotremorine at the prejunctional muscarine receptors was 0.33 μmol/l. In conclusion, the sympathetic nerve terminals in the rabbit trachea are endowed with inhibitory M2-like muscarine receptors for which methoctramine displayed a low affinity. Since a large receptor reserve could be excluded, the steep concentration response curve of oxotremorine suggests that activation of muscarine receptors has to reach a threshold level before the onset of an inhibitory effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00173015
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of histamine H3 receptors inhibiting 5-HT release from porcine enterochromaffin cells: Further evidence for H3 receptor heterogeneity (1994)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 350 (1994), S. 375-379 
    Details
    ISSN: 1432-1912
    Keywords: Enterochromaffin cells ; 5-Hydroxytryptamine release ; Histamine H3 receptors ; Thioperamide ; (R)-α-methyl-histamine ; Imetit ; Porcine small intestine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The nature of the histamine receptor mediating inhibition of 5-HT release was investigated in strips of the porcine small intestine by investigating the effects of histamine ligands on the overflow of endogenous 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA). The overflow was measured by HPLC, combined with electrochemical detection and represents calcium-sensitive 5-HT release from enterochromaffin cells, as reported previously. The histamine H3 receptor selective agonists (R)-α-methyl-histamine and imetit inhibited the overflow of 5-HT maximally by 50–60%, with EC50 values of 48 and 3.2 nmol/l, respectively. Effects on 5-HT overflow were always accompanied by similar effects on the overflow of 5-HIAA. Thioperamide (100 nmol/l) shifted the concentration response curve of (R)-α-methyl-histamine to the right (pKB value 8.38). The inhibitory effect of 1 μmol/l (R)-α-methyl-histamine was antagonized in a concentration-dependent manner by thioperamide (IC50: 65 nmol/l) and dimaprit (IC50: 8.6 μmol/l); however, the effect of (R)-α-methyl-histamine was weakly antagonized by burimamide (by 38% at 100 μmol/l) and not significantly affected by other H3 receptor antagonists, such as impromidine, betahistine and phenylbutanoyl-histamine (each up to 100 μmol/l). In conclusion, H3 receptors mediating inhibition of 5-HT release from porcine enterochromaffin cells have a particular pharmacological profile indicating that heterogeneity of H3 receptors may exist. The data suggest that histamine H3 receptors modulating 5-HT release in pig small intestine do not belong to either H3A or H3B receptors as defined in rat tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00178954
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