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  • Title: Presynaptic alpha 2-adrenoceptors exclusively sensitive to agonists of phenylethylamine structure on the sympathetic nerves of the human gall bladder artery.
    Author: Kapocsi J, Zimanyi I, Farsang C, Vizi ES.
    Journal: Neurosci Res; 1987 Jun; 4(5):413-8. PubMed ID: 2823195.
    Abstract:
    The influence of alpha 2-adrenoceptor agonists and antagonists on the release of noradrenaline was studied in human gall bladder (cystic) artery preparations, in which transmitter stores were labelled with [3H]noradrenaline. The preparations were stimulated at 2 Hz for 3 min (360 shocks each of 1 ms duration two times (S1 and S2)). Both the L-noradrenaline and alpha-methylnoradrenaline (10(-6) M) significantly reduced (S2/S1 = 0.27 +/- 0.05; 0.43 +/- 0.04, respectively), whilst clonidine, xylazine and guanfacine at 10(-6) M failed to affect the stimulation evoked release of [3H]noradrenaline. Yohimbine (10(-6) M), CH-38083, which is a new, selective alpha 2-adrenoceptor antagonist (10(-7) M) and prazosin (10(-6) M) enhanced the evoked release of radioactivity, where S2/S1 were 2.50 +/- 0.19; 2.99 +/- 0.32; 1.48 +/- 0.05, respectively. Administering the alpha 2-antagonists and prazosin together, we were unable to demonstrate an additive effect. Yohimbine and CH-38083 prevented, while prazosin reduced, the inhibitory effects of L-noradrenaline or alpha-methylnoradrenaline on the release of radioactivity. Our results suggest that one type of presynaptic alpha 2-adrenoceptor modulates the release of noradrenaline evoked by electrical stimulation of the human cystic artery. This receptor is sensitive to alpha 2-adrenoceptor agonists which have a phenylethylamine structure, but is insensitive to imidazolines and guanfacine.
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