The effects of some alpha-adrenoceptor antagonists on the responses of the canine saphenous vein to B-HT 933, UK-14304 and methoxamine.

The benzoquinolizines Wy 25309, Wy 26703 and Wy 27127, previously reported as potent antagonists at presynaptic alpha 2-adrenoceptors were also potent antagonists of B-HT 933 in isolated saphenous veins of the dog confirming their activity at post synaptic alpha 2-adrenoceptors. Yohimbine was a more potent antagonist of B-HT 933 in isolated saphenous vein than were the Wy compounds or idazoxan contrasting with the reported potencies of these compounds at presynaptic sites in rat vas deferens and raising the possibility of differences between pre- and postsynaptic alpha 2-adrenoceptors. Contractions of the saphenous vein were observed with high concentrations of idazoxan.