Alpha-adrenergic receptors in human blood vessels

The evidence for the presence of postjunctional alpha 1- and alpha 2-adrenoceptor subtypes in human blood vessels is reviewed. Experiments in healthy subjects are described that show that alpha 1- as well as alpha 2-adrenoceptor mediated vasoconstriction contribute to vascular smooth muscle tone and that adrenaline and noradrenaline have similar affinities for each subtype. In addition, evidence is presented for a preferential intrajunctional location of alpha 1-adrenoceptors and a preferential extrajunctional location of alpha 2-adrenoceptors in human blood vessels. It is concluded that at present postjunctional alpha-adrenoceptors in human blood vessels can be classified as alpha 1 and alpha 2. Despite the fact that both subtypes mediate vasoconstriction, these receptors are likely to subserve different physiological functions.