A difference in the affinity of some selective ?2-adrenoceptor antagonists when compared on isolated vasa deferentia of rat and rabbit

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Abstract
The α2-adrenoceptor antagonist potencies of the benzoquinolizines (Wy 26 703, Wy 25 309, Wy 26 392), the benzodioxans (RX 781 094, RS 21 361), yohimbine and rauwolscine have been compared at presynaptic α2-adrenoceptors in the isolated vasa deferentia of the rat and rabbit. Yohimbine and rauwolscine are of equal potency as antagonists in both the rat and rabbit against the agonists clonidine or UK 14 304. The benzoquinolizines and benzodioxans are very weak antagonists of clonidine or UK 14 304 at the presynaptic α2-adrenoceptors of the rabbit vas deferens when compared to their potency at the presynaptic α2-adrenoceptors of the rat vas deferens. This suggests that the presynaptic α2-adrenoceptors present in the rat vasa deferentia may be different from those present in the rabbit vasa deferentia.