Selective antagonists are available for most of the a1-adrenoceptor subtypes (Table 12.1); however, the degree of selectivity varies, and consistent results between functional and radioligand binding assays is not always observed (Stam et al. 1998). Classically, though SNAP-5089, L765314, and SKF105854 are used to block a1A, a1B, and a1D adrenoceptors, respectively. a2 adrenoceptor mediated effects are classically differentiated from a1 in that the former are sensitive to antagonists such as yohimbine and idazoxan. Within the a2 adrenoceptor family a2A- and a2D-adrenoceptor mediated responses can be differentiated by the low sensitivity of the a2D - adrenoceptor to blockade by the commonly used antagonists, yohimbine, and rauwolscine (Bylund et al. 1995; Hieble et al. 1996).
Many useful pharmacological tools are available for (-adrenoceptor characterization. These include antagonists selective for p1-, (2-, or (^-adrenoceptors subtypes such as atenolol, ICI118551 and SR58894, respectively (Hieble 1991).
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