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  • 1
    Electronic Resource
    Electronic Resource
    Effects of flow-stop on the metabolism of noradrenaline released by nerve stimulation in the perfused spleen (1973)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 278 (1973), S. 179-194 
    Details
    ISSN: 1432-1912
    Keywords: Noradrenaline ; Noradrenaline Metabolites ; Perfused Spleen ; Nerve Stimulation ; Transmitter Overflow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The metabolic pathway of 3H-noradrenaline released spontaneously and by nerve stimulation was studied in the isolated perfused spleen of the cat. The deaminated glycol, DOPEG, (3,4 dihydroxyphenylglycol) was the main metabolite in spontaneous outflow, accounting for 62.5±1.6% of the total radioactivity (n=13). Of the total increase in radioactive products elicited by nerve stimulation at 5 Hz or 10 Hz around 30% was accounted for by the noradrenaline metabolites, particularly DOPEG and the O-methylated fraction. In the presence of 2.9×10−6 M of cocaine the total overflow of radioactivity induced by stimulation was unchanged but DOPEG formation from released noradrenaline was abolished. These findings indicate that DOPEG formation results from the recapture of the released transmitter by adrenergic nerve endings and subsequent intraneuronal deamination. The total overflow of noradrenaline was reduced by flow-stop while the metabolism of the released transmitter was increased significantly. Cocaine, 2.9×10−6 M, prevented the increase in DOPEG when stimulation was applied under flow-stop conditions. The decrease in noradrenaline overflow induced by flow-stop is partly due to the increase in the metabolism of the released transmitter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00500649
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Inhibition by dopamine of 3H-noradrenaline release elicited by nerve stimulation in the isolated cat's nictitating membrane (1975)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 289 (1975), S. 179-203 
    Details
    ISSN: 1432-1912
    Keywords: Nerve Stimulation ; Noradrenaline ; Dopamine ; Nictitating Membrane ; Neurotransmission ; α-Adrenoceptors ; Dopamine Receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary After loading the isolated nerve-muscle preparation of the cat nictitating membrane with 3H-(±)-noradrenaline the effects of exogenous dopamine and (-)-noradrenaline were determined on 3H-transmitter overflow elicited by nerve stimulation in the presence of cocaine, 29 μM. Dopamine, 0.20 μM, and (-)-noradrenaline, 0.18 μM, inhibited 3H-noradrenaline release elicited by nerve stimulation at 4 or 10 Hz. Similar results were obtained with apomorphine 0.03 or 0.1 μM. Chlorpromazine, 1 μM, or pimozide, 1 μM, antagonized selectively the reduction in 3H-noradrenaline release obtained with dopamine or apomorphine, without affecting the inhibition obtained with (-)-noradrenaline. Phentolamine, 1 μM, antagonized more effectively the inhibitory effects of (-)-noradrenaline than those of dopamine. Phenoxybenzamine, 0.29 μM, prevented the inhibition of 3H-transmitter overflow obtained with (-)-noradrenaline, dopamine or apomorphine. In the absence of cocaine neither chlorpromazine nor pimozide were able to increase 3H-transmitter overflow during nerve stimulation. In contrast to these results, block of α-adrenoceptors by phentolamine or phenoxybenzamine resulted in an increase 3H-transmitter overflow during nerve stimulation. Inhibition by dopamine of 3H-transmitter overflow appears to be mediated through dopamine receptors probably located in the outer surface of adrenergic nerve endings. These dopamine receptors differ from the prejunctional α-adrenoceptors that mediate the negative feed-back regulatory mechanism for noradrenaline release by nerve stimulation. The prejunctional inhibitory dopamine receptors are not involved in an endogenously mediated regulatory mechanism for noradrenaline release by nerve stimulation under normal conditions. The possibility that these dopamine receptors are involved in the hypotension commonly observed in patients with chronic l-Dopa treatment is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00501305
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  • 3
    Electronic Resource
    Electronic Resource
    Prejunctional effects of a purified toxin from the scorpion Tityus serrulatus (1975)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 287 (1975), S. 243-259 
    Details
    ISSN: 1432-1912
    Keywords: Scorpion Toxin ; Noradrenaline ; Noradrenaline Metabolites ; Guinea-Pig Atria ; Nerve Stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of a purified fraction of the venom of the Brazilian scorpion, Tityus serrulatus, were studied in isolated guinea-pig atria previously labelled with 3H-noradrenaline. Exposure to 0.3 and 1.0 μ/ml of the scorpion toxin resulted in a long lasting positive chronotropic effect which was concentration-dependent. The increase in atrial rate coincided with an enhancement in spontaneous outflow of radioactivity. The increase in outflow of radioactive products elicited by exposure to 1.0 μg/ml of the scorpion toxin was approximately 3-fold. 3H-noradrenaline accounted for 60% of the total increase in outflow of radioactivity elicited by the scorpion toxin and the 3H-deaminated glycol (3,4-dihydroxyphenylglycol) represented the main metabolite formed, accounting for approximately 35% of the total release. 20 min after exposure to 1.0 μg/ml of the scorpion toxin the overflow of the labelled transmitter elicited by accelerans nerve stimulation (4 Hz, during 60 sec, supramaximal voltage) was increased 8-fold. This effect of the scorpion toxin appears to be unrelated to inhibition of neuronal uptake, block of α-adrenoceptors or stimulation of β-adrenoceptors. Consequently, in addition to releasing noradrenaline, the scorpion toxin enhances transmitter overflow elicited by nerve stimulation through a prejunctional effect which appears to reflect a nove mechanism of action.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00501471
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Selective inhibition by hydrocortisone of 3H-normetanephrine formation during 3H-transmitter release elicited by nerve stimulation in the isolated nerve-muscle preparation of the cat nictitating membrane (1975)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 287 (1975), S. 261-275 
    Details
    ISSN: 1432-1912
    Keywords: Nerve Stimulation ; Noradrenaline Metabolites ; Hydrocortisone ; Extraneuronal Uptake ; Normetanephrine ; Nictitating Membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The metabolism of 3H-noradrenaline released by nerve stimulation in the isolated nerve-muscle preparation of the cat nictitating membrane was determined under control conditions and in the presence of hydrocortisone, 28 μM, a concentration which inhibits the high affinity extraneuronal uptake of noradrenaline in this tissue. in the controls the main fraction in the overflow elicited by stimulation at 10 Hz during 2 min was the deaminated glycol, 3H-DOPEG (3,4-dihydroxyphenylglycol), which accounted for 45.2±2.96% of the total radioactivity. Under these conditions, 3H-noradrenaline represented 30.8±1.92%, while 3H-normetanephrine accounted for 14.5±0.94% of the total overflow of radioactivity. During exposure to hydrocortisone there was a selective inhibition in 3H-normetanephrine formation from 3H-noradrenaline released by stimulation while the other fractions were not affected significantly. In contrast to these results, there were no changes in the spontaneous outflow of 3H-normetanephrine during exposure to hydrocortisone. The results obtained support the view that 3H-normetanephrine in sponteneous release originates from the activity of prejunctional catechol-O-methyltransferase. On the other hand, 3H-normetanephrine formed during transmitter release elicited by nerve stimulation is due to the activity of extraneuronal catechol-O-methyltransferase. Access of 3H-noradrenaline released by nerve stimulation to extraneuronal catechol-O-methyltransferase is mediated through the high-affinity, hydrocortisone-sensitive extraneuronal uptake mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00501472
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    Paper (German National Licenses)
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