Specific alpha-adrenoceptor-mediated vasoconstriction in human veins and interaction with the calcium entry blockers nifedipine and diltiazem.

In order to characterize the pharmacological properties of post-junctional alpha-adrenoceptors, the vasoconstricting effects of the non-specific alpha-adrenoceptor agonist noradrenaline, of the specific alpha 1-adrenoceptor agonist phenylephrine and of the specific alpha 2-adrenoceptor agonist azepexole and the interaction with the calcium entry blockers nifedipine and diltiazem were studied in hand veins of eight healthy volunteers. Both subtypes of alpha-adrenoceptors could be demonstrated in human hand veins in vivo. The alpha 1-subtype seemed to prevail. Vasoconstriction induced by stimulation of either post-synaptic alpha 1- or alpha 2-adrenoceptors was reduced by the calcium entry blockers diltiazem and nifedipine.