Do low‐affinity states of β‐adrenoceptors have roles in physiology and medicine?

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Abstract
The pharmacology once ascribed to the ‘β4‐adrenoceptor’ is now believed to be that of a low‐affinity state of the β1‐adrenoceptor. The β2‐adrenoceptor may also have a low‐affinity state or site, while the β3‐adrenoceptor – the original low‐affinity β‐adrenoceptor – can display more than one pharmacology. In this issue, Mallem et al. show that CGP‐12177 relaxes thoracic aorta rings from normal rats by stimulating vascular smooth muscle low‐affinity β1‐adrenoceptors, apparently linked in part to Gi protein. By contrast, in rings from hypertensive rats, CGP‐12177 acts mainly via endothelial β3‐adrenoceptors. This work raises the possibility that low‐affinity states of β‐adrenoceptors have physiological roles, and suggests that they might be drug targets.British Journal of Pharmacology (2004) 143, 517–518. doi:10.1038/sj.bjp.0705991