The most selective a1A-adrenoceptor subtype agonists that are currently available include SKF-89748 and A61603. No selective agonists are available for the a1B- or a1D-adrenoceptor subtype. A similar situation applies to a2-adrenoceptors. Thus, for the a2A-adrenoceptor subtype guanfacine and oxymetazoline are the agonists of choice although the latter exhibits only partial agonist activity at this receptor subtype and is a full agonist at a1A-adrenoceptors. Many more useful pharmacological tools are available for (-adrenoceptor characterization. Thus, agonists capable of selectively activating p1-, (2-, or (^-adrenoceptors such as xamoterol, salbutamol, and BRL37344 are frequently used to characterize the functional effects of these receptor subtypes, respectively. Species differences appear to be important for the (^-adrenoceptor, since several selective (3-adrenoceptor agonists can activate rodent, but not human, (3-adrenoceptors.
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