ABSTRACT
The a 1L-adrenoceptor also appears to mediate contraction of several blood vessels (113). Many antagonists, including those capable of differentiating between a 1a-and a 18-adrenoceptors, do not discriminate between the a 1a-and a 1L-adrenoceptors (115). The low potency of RS 17053 against phenylephrine-reduced contraction of the rat portal vein (86) suggests that the a 1L-adrenoceptor mediates this response, in contrast to the high potency of this antagonist in the perfused rat kidney where a 1A-adrenoceptors are presumably involved (76). Again, studies on the potential role of the a 1Ladrenoceptor in regulation of vascular tone have been limited by the lack of antagonists that antagonize a 1L-but not am-adrenoceptors. Some recently identified compounds have this profile (116).
