title: Vasoconstriction mediated by postsynaptic alpha 2-adrenoceptor stimulation.
abstract: The postsynaptic alpha-adrenoceptors involved in vasoconstriction brought about by B-HT 933 (2-amino-6-ethyl-4,5,7,8-tetrahydro-6H-oxazolo-[5,4-d]-azepin) administered i.v. to pithed, normotensive rats were characterized. The rate of onset of the hypertensive response to i.v. B-HT 933 is slower than that induced by (-)-phenylephrine, an agonist of alpha 1-adrenoceptors. The antagonism of the alpha-adrenoceptor blocking drugs rauwolscine, yohimbine and corynanthine was quantified towards B-HT 933-induced increases in diastolic pressure. Rauwolscine (pA2 = 7.06) and yohimbine (pA2 = 6.83) were effective antagonists, whereas corynanthine proved much less potent (pA2 = 5.03). On the basis of the reported selectivity of yohimbine and its two diastereoisomers rauwolscine and corynanthine for alpha 1- and alpha 2-adrenoceptors, it is concluded that the postsynaptic alpha-adrenoceptors triggered by B-HT 933 are of the alpha 2-type. B-HT 933 identifies a subclass of postsynaptic alpha 2-adrenoceptors in vascular smooth muscle distinct from postsynaptic alpha 1-adrenoceptors. Both types of alpha-adrenoceptors are likely to be involved in the mediation of vasoconstriction.
mesh_terms: D000818:Animals; D001381:Azepines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D008297:Male; D010080:Oxazoles / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D015016:Yohimbine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D001381:Azepines; D010080:Oxazoles; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D015016:Yohimbine; C015603:azepexole