Differences between the alpha 2-adrenoceptor in rat submaxillary gland and the alpha 2A-and alpha 2B-adrenoceptor subtypes.
1. The alpha 2-adrenoceptors of rat submaxillary gland, labelled with [3H]-rauwolscine, were characterized by use of a range of subtype selective ligands and were compared to rabbit spleen alpha 2A-adrenoceptors and rat kidney alpha 2B-adrenoceptors. 2. In rat submaxillary gland, [3H]-rauwolscine labelled an apparently homogeneous population of binding sites with relatively low affinity (Kd = 11.65 nM) compared to the affinity in rat kidney (Kd = 2.18 nM) and rabbit spleen (Kd = 4.64 nM). 3. In competition studies using 16 ligands the alpha 2-adrenoceptors in rat submaxillary gland appeared to differ from both the alpha 2A-adrenoceptor of rabbit spleen (r = 0.62) and also the alpha 2B-adrenoceptor of rat kidney (r = 0.28). 4. The affinity data obtained with benoxathian, imiloxan and WB 4101 indicated the presence of an alpha 2B-adrenoceptor in rat submaxillary gland. However, data for chlorpromaxine, oxymetazoline, spiroxatrine and xylometazoline indicated that submaxillary gland alpha 2-adrenoceptors were of the alpha 2A subtype. The affinity estimate for prazosin in rat submaxillary gland was intermediate between its affinity at the alpha 2A- and alpha 2B-adrenoceptors while affinity estimates for idazoxan and phentolamine in rat submaxillary gland were greater than those obtained at either the alpha 2A- or alpha 2B-adrenoceptor. 5. These data indicate that rat submaxillary gland alpha 2-adrenoceptors differ from the alpha 2A- and alpha 2B-adrenoceptors found in rabbit spleen and rat kidney, respectively.
Michel
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Institute of Pharmacology, Syntex Research, Palo Alto, CA 94303.
Loury
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Whiting
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D000818:Animals; D001667:Binding, Competitive; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D013045:Species Specificity; D013154:Spleen / Q000378:metabolism; D013363:Submandibular Gland / Q000378:metabolism*
D011942:Receptors, Adrenergic, alpha