Smooth muscle of rabbit aorta contains alpha 1-but not alpha 2-adrenoceptors.

We have investigated the residual contractile response to noradrenaline remaining after phenoxybenzamine (3 x 10(-7) mol/l) in rabbit aorta, since it has been reported that phenoxybenzamine at low doses completely and irreversibly blocks alpha 1-but not alpha 2-adrenoceptors. The contraction elicited by noradrenaline slowly recovered with time after it had been almost abolished by phenoxybenzamine. This residual response was blocked by the alpha 1-selective antagonist prazosin (3 x 10(-8) mol/l) but not by the alpha 2-selective antagonist rauwolscine (3 x 10(-7) mol/l). The results confirm that the smooth muscle of rabbit aorta contains alpha 2-but not alpha 2-adrenoceptors.