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.