PT - JOURNAL ARTICLE AU - Naselsky, Diane P. AU - Ashton, Daryl AU - Ruffolo, Robert R. AU - Hieble, J. Paul TI - Rabbit α<sub>2</sub>-Adrenoceptors: Both Platelets and Adipocytes Have α<sub>2A</sub>-Pharmacology DP - 2001 Jul 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 219--225 VI - 298 IP - 1 4099 - http://jpet.aspetjournals.org/content/298/1/219.short 4100 - http://jpet.aspetjournals.org/content/298/1/219.full SO - J Pharmacol Exp Ther2001 Jul 01; 298 AB - The recombinant α2-adrenoceptors, designated as α2a and α2d, have highly similar amino acid sequences, but distinct pharmacological properties. It has been suggested that these two receptor subtypes are species orthologs, since the α2-adrenoceptors of a given species have pharmacological characteristics corresponding to either the α2a- (human, pig) or α2d- (rat, mouse, guinea pig, cow) adrenoceptor. Radioligand binding assays in rabbit adipocyte suggest α2D-adrenoceptor pharmacology. However, functional studies examining prejunctional α2-adrenoceptors in several tissues pharmacologically define the receptor of the rabbit as an α2A-adrenoceptor rather than an α2D-adrenoceptor. We characterized the α2-adrenoceptor of rabbit adipocyte and platelet, comparing the ability of norepinephrine and 13 adrenoceptor antagonists to inhibit the binding of [3H]RX821002 with the affinity of these drugs for the human α2a-adrenoceptor or the rat α2d-adrenoceptor. Pharmacological characteristics of the adipocyte and platelet receptor were very similar, with an excellent correlation between pKi values (r2 = 0.95, slope of regression = 1.01). Drug affinities for both platelet and adipocyte receptors correlated better with the α2a-adrenoceptor (r2 = 0.68–0.77) than with the α2d-adrenoceptor (r2 = 0.37–0.38). Despite the relatively low affinity of the rabbit adipocyte α2-adrenoceptor for yohimbine and rauwolscine, this receptor, as well as the platelet receptor, have α2A-adrenoceptor pharmacology. Subtle differences in the α2-adrenoceptor binding characteristics of these native rabbit tissues compared with the recombinant human α2a-adrenoceptor may result either from minor differences in the sequence of human and rabbit α2a-adrenoceptors or from differences in the environment to which native and recombinant receptors are exposed. The American Society for Pharmacology and Experimental Therapeutics