ALPHA(1)-ADRENOCEPTOR SUBTYPES AND 2 RECEPTOR SYSTEMS IN VASCULAR TISSUES

The subtypes of alpha(1)-adrenoceptor are coexpressed in many tissues. We examined the relationship between coexpressed alpha(1)-adrenocepto r subtypes and their functions in blood vessels. Rat and rabbit aortas coexpressed three subtypes (alpha(1A), alpha(1B), alpha(1D)) and four subtypes (alpha(1A), alpha(1B), alpha(1D), alpha(1L)), respectively. In rat aorta however, noradrenaline-induced contraction was mediated p redominantly through the alpha(1D) subtype, and oxymetazoline produced alpha(1B)-mediated contraction. In rabbit aorta, concentration-respon se curves for noradrenaline were composed of two components (alpha(1B) and alpha(1L)-mediated), while oxymetazoline produced alpha(1L)-media ted contraction. Therefore, the inhibitory actions of some antagonists varied markedly among tissues and agonists. These results demonstrate diversity of the two receptor systems and suggest that the heterogene ity of physiological responses reflects the differences in functional subtypes among tissues and in their sensitivities to agonists and anta gonists.