CHARACTERIZATION OF CONTRACTILE ADRENOCEPTORS IN THE HUMAN UMBILICAL ARTERY

Adrenoceptors mediating contraction in ring segments of human umbilica l arteries from normal term pregnancies were investigated in vitro. Co ntraction was elicited by (order of potency indicated): noradrenaline = the alpha(2)-adrenoceptor agonist oxymetazoline >> the alpha(1)-adre noceptor agonist phenylephrine. The alpha(1)-adrenoceptor antagonist p razosin antagonized the contraction elicited by noradrenaline and phen ylephrine. The alpha(2)-adrenoceptor antagonist rauwolscine antagonize d the contraction elicited by noradrenaline and oxymetazoline. Oxymeta zoline had an efficacy 5 times higher than that of noradrenaline and t he 5-hydroxytryptamine receptor antagonist methysergide antagonized th e contraction elicited by oxymetazoline. It is suggested that the cont ractile adrenoceptors in the human umbilical artery consist of both al pha(1) and alpha(2) subtypes. Furthermore, the contractile effect of o xymetazoline seems to be mediated via both alpha(2)-adrenoceptors and 5-hydroxytryptamine receptors.