title: Relation between density (maximum binding) of alpha adrenoceptor binding sites and contractile response in four canine vascular tissues.
abstract: In microsomal fractions from dog aorta, saphenous veins, mesenteric arteries and veins, both [3H]prazosin and [3H]rauwolscine displayed monophasic saturation in binding. The Kd for [3H] rauwolscine binding was similar for all these blood vessels, but the maximum number of [3H]rauwolscine binding sites was 3 to 7 times higher in veins compared to arteries. The Kd for [3H] prazosin was higher in saphenous vein than that in the arteries. The maximum number of binding sites for [3H]prazosin was similar, except for that in aorta, which was 3 times greater. Phenylephrine (alpha-1 adrenoceptor selective agonist) or norepinephrine (nonselective adrenoceptor agonist) produced similar maximal responses in all vessels. The alpha-2 adrenoceptor selective agonist, B-HT 920 (2-amino-6-allyl-3,4,7,8-tetrahydro-6H-thiazolo[5,4-d]-azepine)-induced contraction in veins but not in arteries. Prazosin (10(-6) M) inhibited completely the contractions to norepinephrine (3 x 10(-6) M) in mesenteric arteries and to phenylephrine (3 x 10(-6) M) in arteries and veins. Contractile responses of mesenteric artery were unaffected by rauwolscine. Rauwolscine (10(-7) M) caused a greater parallel rightward shift of the concentration-response curve to norepinephrine than did prazosin (10(-7) M) in saphenous veins, and a further rightward shift of responses to norepinephrine after 10(-7) M prazosin in mesenteric vein and saphenous vein and abolished B-HT 920-induced responses at alpha-2 adrenoceptors. The tissues responding to B-HT-920 correspond to those having the highest alpha-2 receptor density as measured by [3H]rauwolscine binding. The density of such sites required for contraction to be initiated in veins was much higher than with alpha-1 adrenoceptor sites.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Neurosciences, Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada.
authors.forename: A G
authors.initials: AG
authors.lastname: Shi
authors.forename: C Y
authors.initials: CY
authors.lastname: Kwan
authors.forename: E E
authors.initials: EE
authors.lastname: Daniel
mesh_terms: D000818:Animals; D001011:Aorta / Q000502:physiology; D001381:Azepines / Q000494:pharmacology; D004285:Dogs; D066298:In Vitro Techniques; D008638:Mesenteric Arteries / Q000502:physiology; D008642:Mesenteric Veins / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D014666:Vasomotor System / Q000502:physiology*; D014680:Veins / Q000502:physiology; D015016:Yohimbine / Q000378:metabolism
chemical_list: D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; C024763:talipexole; D009638:Norepinephrine; D011224:Prazosin