Characterization of postsynaptic α‐adrenoceptors in rat aortic strips and portal veins

• Published in: British journal of pharmacology 1983-07, Vol.79 (3), p.655-665
• Main Authors: Digges, K.G., Summers, R.J.
• Format: Article
• Language: English
• Subjects: Adrenergic alpha-Agonists - pharmacology; Adrenergic alpha-Antagonists - pharmacology; alpha -adrenergic; Animals; Aorta - physiology; Clonidine - pharmacology; Female; Male; Muscle, Smooth, Vascular - physiology; Nordefrin - pharmacology; Oxymetazoline - pharmacology; Phenethylamines - pharmacology; Portal Vein - physiology; Prazosin - pharmacology; Rats; Rats, Inbred Strains; Receptors, Adrenergic, alpha - drug effects; smooth muscle; Tetralones; Yohimbine - pharmacology
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1983.tb10002.x

1 Postsynaptic α‐adrenoceptors in rat isolated aortic strips and portal veins have been examined using a number of agonist and antagonist drugs which have varying selectivity for α1‐ and α2‐adrenoceptors. 2 In both tissues (−)‐noradrenaline ((−)‐NA), (−)‐adrenaline ((−) Adr) (−)‐α‐methyl noradrenaline ((−)‐α‐Me‐NA) and (−)‐phenylephrine ((−)‐PE) were full agonists, while clonidine, oxymetazoline and (2‐(2,6‐dichlorophenyl)‐5,6‐dihydroimidazo(2,1,b) thiazole (44,549) were partial agonists. Guanfacine was a full agonist in aortic strips but only a partial agonist in portal veins. 3 In aortic strips, pA2 values for prazosin and yohimbine were not significantly different using (−)‐NA, (−)‐PE or guanfacine as the agonist, suggesting a single population of α‐adrenoceptors. The order of potency of the antagonists, prazosin = 2‐(β‐(4‐hydroxyphenyl)‐ethylaminomethyl)‐tetralone (BE2254) > phentolamine > yohimbine > rauwolscine, is indicative of an α1‐type of receptor. 4 In portal veins, the order of potency of the antagonists was prazosin > BE2254 > phentolamine > yohimbine > rauwolscine, again indicating an α1‐type of receptor. 5 The mean pA2 value for yohimbine was not significantly different in either tissue. However, mean pA2 values for prazosin, BE‐2254 and phentolamine were approximately one order of magnitude lower in portal veins than in aortic strips, suggesting that the receptors in the two tissues may not be identical.