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

<jats:p><jats:list list-type="explicit-label"> <jats:list-item><jats:p>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 α<jats:sub>1</jats:sub>‐ and α<jats:sub>2</jats:sub>‐adrenoceptors.</jats:p></jats:list-item> <jats:list-item><jats:p>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.</jats:p></jats:list-item> <jats:list-item><jats:p>In aortic strips, pA<jats:sub>2</jats:sub> 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 α<jats:sub>1</jats:sub>‐type of receptor.</jats:p></jats:list-item> <jats:list-item><jats:p>In portal veins, the order of potency of the antagonists was prazosin > BE2254 > phentolamine > yohimbine > rauwolscine, again indicating an α<jats:sub>1</jats:sub>‐type of receptor.</jats:p></jats:list-item> <jats:list-item><jats:p>The mean pA<jats:sub>2</jats:sub> value for yohimbine was not significantly different in either tissue. However, mean pA<jats:sub>2</jats:sub> 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.</jats:p></jats:list-item> </jats:list></jats:p>