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No evidence for differences between pre‐ and postjunctional α 2 ‐adrenoceptors in the periphery
Author(s) -
Connaughton Sonia,
Docherty J.R.
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb14660.x
Subject(s) - yohimbine , vas deferens , prazosin , endocrinology , phentolamine , medicine , phenylephrine , stimulation , oxymetazoline , agonist , guinea pig , chemistry , receptor , biology , antagonist , blood pressure
1 We have compared prejunctional α 2 ‐adrenoceptors in rat and guinea‐pig vas deferens and rat and guinea‐pig atria with postjunctional α 2 ‐adrenoceptors in human saphenous vein and human platelets employing the antagonists yohimbine and SK&F 104078 and other α 2 ‐adrenoceptor antagonists. 2 Yohimbine was approximately 10 times more potent prejuunctionally than SK&F 104078 at antagonizing the inhibition by the α 2 ‐adrenoceptor agonist xylazine of stimulation‐evoked contractions in rat and guinea‐pig vas deferens, and at increasing stimulation‐evoked release of tritium in rat and guinea‐pig atria pre‐incubated with [ 3 H]‐noradrenaline. 3 Yohimbine was approximately 10 times more potent postjunctionally than SK&F 104078 at antagonizing contractions to noradrenaline in human saphenous vein and at displacing [ 3 H]‐yohimbine binding in human platelet membranes. 4 For the antagonists yohimbine, SK&F 104078, prazosin, phentolamine, CH 38083 and urapidil, there was a significant correlation between prejunctional potency in rat vas deferens atrium and postjunctional potency in human platelet, although the correlation was improved by the omission of prazosin. 5 We have no evidence for differences between functional pre‐ and postjunctional α 2 ‐adrenoceptors in the periphery, although these functional receptors may differ from the ligand binding site in the human platelet.