Characterisation of postjunctional ?-adrenoceptors in isolated human femoral veins and arteries

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Abstract
In order to characterise the pharmacological properties of postjunctional α-adrenoceptors, both the contractile effects of α-adrenoceptor agonists and the blocking potencies of selective α-adrenoceptor antagonists were studied in isolated human femoral veins and arteries. The veins were more sensitive to noradrenaline than the arteries. Guanfacine had a higher intrinsic activity in veins than in arteries, whereas the reverse was true for phenylephrine. The antagonists rauwolscine and yohimbine were more potent against noradrenaline in the veins than in arteries, while corynanthine was equally potent in either tissue. They antagonised the noradrenaline response in a competitive manner. Prazosin proved to be the most potent competitive antagonist in arteries, while in veins it exerted weak and noncompetitive antagonism. The results suggest that the α-adrenoceptor population at the postjunctional site differs between human femoral veins and arteries. The veins seem to contain more α2- than α1-adrenoceptors postjunctionally, whereas in the arteries the α2-subtype prevails. The results indicate the possibility of influencing selectively adrenergic reactions in the capacitance and resistance vessels.