Location of vascular alpha 2-adrenoceptors in man

To determine whether vascular postsynaptic alpha 2-adrenoceptors are innervated by sympathetic nerves in man, normal volunteers were infused for 90 min with angiotensin II (A II) and the alpha 2-adrenoceptor agonist alpha-methylnoradrenaline (MNA) in a double-blind cross-over study. Whilst systolic blood pressure returned to baseline within 5 min of terminating the A II infusion it remained elevated 40 min after stopping MNA. The prolongation of the pressor response to MNA, a substrate for neuronal uptake, was probably due to activation of alpha 2-adrenoceptors by MNA re-released from contiguous sympathetic nerve endings. The proximity of alpha 2-adrenoceptors to sympathetic nerve terminals suggests that they could contribute to blood pressure regulation in man.