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Evidence that the population of postjunctional‐adrenoceptors mediating contraction of smooth muscle in the rabbit isolated ear vein is predominantly α 2
Author(s) -
Daly C.J.,
McGrath J.C.,
Wilson V.G.
Publication year - 1988
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.1476-5381.1988.tb11626.x
Subject(s) - rauwolscine , prazosin , yohimbine , phenylephrine , potency , schild regression , medicine , endocrinology , population , competitive antagonist , contraction (grammar) , muscle contraction , chemistry , antagonist , biology , receptor , biochemistry , in vitro , environmental health , blood pressure
1 Noradrenaline (NA), phenylephrine and UK‐14304 elicited concentration‐dependent contractions of the rabbit isolated ear vein of similar maximal magnitude. The rank order of potency, UK‐14304 > noradrenaline > phenylephrine, is consistent with that of an effect mediated through an α 2 ‐subtype. 2 The potent and highly selective α 1 ‐adrenoceptor antagonists prazosin and YM‐12617, at concentrations as high as 1 μ m , produced less than a 4 fold rightward displacement of the NA concentration‐response curve. 3 The selective α 2 ‐adrenoceptor antagonists rauwolscine, Wy‐26703 and CH‐38083 antagonized responses to noradrenaline in a competitive manner. For all three antagonists, the pA 2 values were consistent with an effect at α 2 ‐adrenoceptors. However, 0.1 μm YM‐12617 increased the potency of rauwolscine 2 fold indicating the presence of a small population of postjunctional α 1 ‐adrenoceptors. 4 The relative antagonist potency of the yohimbine diastereoisomers rauwolscine and corynanthine against noradrenaline (rauwolscine 30 fold > corynanthine) is also consistent with an effect at α 2 ‐adrenoceptors. 5 Contractions elicited by noradrenaline in the rabbit isolated ear vein appear to be mediated predominantly by postjunctional α 2 ‐adrenoceptors.