title: Postsynaptic alpha 1- and alpha 2-adrenoceptors in the circulatory system of the pithed rat: selective stimulation of the alpha 2-type by B-HT 933.
abstract: The antagonism by yohimbine (1 mg/kg, i.v.) of vasopressor responses in pithed rats was most pronounced towards B-HT 933 (dose ratio 18.3) and moderate towards clonidine (dose ratio 3.7) and especially L-phenylephrine (dose ratio 2.5). Prazosin (0.1 mg/kg, i.v.) had no effect on the pressor responses to B-HT 933, moderately affected those to clonidine (dose ratio 3.9), but strongly diminished those to L-phenylephrine (dose ratio 53). Phentolamine (1 mg/kg, i.v.) was devoid of a differential antagonism. The results obtained suggest a subclassification of postsynaptic alpha-adrenoceptors into alpha 1- and alpha 2-subtypes mediating pressor effects. B-HT 933 is a selective agonist and yohimbine an antagonist of postsynaptic alpha 2-adrenoceptors. L-Phenylephrine preferably stimulates and prazosin preferentially occupies the alpha 1-adrenoceptors. Clonidine is a potent agonist of both types and phentolamine behaves as a non-selective antagonist.
mesh_terms: D000818:Animals; D001381:Azepines / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D010080:Oxazoles / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000032:analysis*; D011942:Receptors, Adrenergic, alpha / Q000032:analysis* / Q000187:drug effects; D017981:Receptors, Neurotransmitter / Q000145:classification / Q000187:drug effects; D014666:Vasomotor System / Q000032:analysis* / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D001381:Azepines; D010080:Oxazoles; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D017981:Receptors, Neurotransmitter; D010656:Phenylephrine; D015016:Yohimbine; C015603:azepexole; D003000:Clonidine; D011224:Prazosin; D010646:Phentolamine