title: Identification and characterization of platelet α2-adrenoceptors and imidazoline receptors in rats, rabbits, cats, dogs, cattle, and horses.
abstract: This study aimed to pharmacologically identify and characterize α2-adrenoceptors and imidazoline (I) receptors (I1- and I2-subtype) on canine, feline, bovine, equine, murine, and leporine platelet membranes. Saturation binding studies with both (3)H-yohimbine and (3)H-clonidine showed that α2-adrenoceptors were expressed on canine, leporine, feline, and murine platelets but not on bovine and equine platelets. In competition studies, the rank order of affinity of 6 compounds for canine platelet α2-adrenoceptors was similar to that of potency at α2A-subtype reported in human platelets. Saturation binding studies in the presence of norepinephrine showed that canine, feline, bovine, and equine platelets had I1-receptors defined by (3)H-clonidine binding, but neither murine nor leporine platelets had I1-receptors; whereas, platelets of all species had I2-receptors defined by (3)H-idazoxan binding. In competition studies, more potent compounds displayed biphasic competition curves with (3)H-clonidine. The rank orders of affinity of I1 compounds for high-affinity components of I1-receptors of canine, feline, bovine, and equine platelets and I2-receptors of all species platelets were similar to those of compounds for high-affinity components reported in human I1- and I2-receptors, respectively. Guanine nucleotides inhibited the high-affinity component of naphazoline binding to canine I1-receptors, but not to I2-receptors. Furthermore, guanine nucleotides dose-dependently inhibited (3)H-clonidine binding to I1-receptors; whereas, they did not interfere with (3)H-idazoxan binding to I2-receptors, supporting the notion that Il-receptors may belong to a G protein-coupled receptor superfamily in canine platelets. Interspecific variations of platelet α2-adrenoceptor and imidazoline receptor expressions may explain different platelet responses to catecholamines and imidazoline α-adrenergic agents.
authors.affiliation: Department of Veterinary Internal Medicine, Faculty of Agriculture, Tottori University, Koyama-Minami 4-101, Tottori 680-8553, Japan. Electronic address: hikasa@muses.tottori-u.ac.jp.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Hikasa
authors.forename: Kyoko
authors.initials: K
authors.lastname: Masuda
authors.forename: Yuki
authors.initials: Y
authors.lastname: Asakura
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yamashita
authors.forename: Chie
authors.initials: C
authors.lastname: Sato
authors.forename: Masae
authors.initials: M
authors.lastname: Kamio
authors.forename: Ayako
authors.initials: A
authors.lastname: Miura
authors.forename: Takuya
authors.initials: T
authors.lastname: Taniguchi
authors.forename: Nao
authors.initials: N
authors.lastname: Minamizuru
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism*; D002415:Cats; D002417:Cattle; D004285:Dogs; D005260:Female; D006736:Horses; D054755:Imidazoline Receptors / Q000378:metabolism*; D008297:Male; D011817:Rabbits; D011869:Radioligand Assay; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*
chemical_list: D054755:Imidazoline Receptors; D018341:Receptors, Adrenergic, alpha-2
keywords: Catecholamine; Imidazoline receptor; Mammalian; Platelet; α(2)-adrenoceptor; α-adrenergic agents