[3H]dihydroergocryptine binding to alpha-adrenoceptors in human femoral veins and arteries.

In order to characterise subtypes of alpha-adrenoceptors in human vascular tissue, radioligand binding studies with [3H]dihydroergocryptine were carried out in human femoral veins and arteries. Binding of [3H]dihydroergocryptine to venous and arterial membranes was rapid and reversible reaching steady state within 4-6 min at 25 degrees C. [3H]Dihydroergocryptine was displaced from its receptor site on vascular membranes by unlabelled alpha-adrenoceptor agonists and antagonists in a concentration-dependent manner. Yohimbine and guanfacine which possess high affinity for alpha 2-adrenoceptors were more effective in competing for [3H]dihydroergocryptine binding sites in veins than in arteries. Prazosin and phenylephrine with high affinity for alpha 1-adrenoceptors were more effective displacers in arteries than in veins. The results suggest that the alpha-adrenoceptor population differs between human femoral veins and arteries. In veins, predominantly alpha 2-adrenoceptors are present, whereas in arteries the adrenoceptor of the alpha 1 type prevails. The results show that the uneven distribution of alpha 1- and alpha 2-adrenoceptors as has been found in animal experiments and pharmacological investigations with human vessels could also be demonstrated by binding studies with [3H]dihydroergocryptine in human femoral arteries and veins.