NO EVIDENCE FOR DIFFERENCES BETWEEN PRE-JUNCTIONAL AND POST-JUNCTIONAL ALPHA-2-ADRENOCEPTORS

1 We have examined the pre- and post-junctional effects of a series of .alpha.-adrenoceptor agonists and antagonists at .alpha.2-adrenoceptors in the pithed rat preparation and the human isolated saphenous vein. 2 In the pithed rat, there was no differnce in relative agonist and antagonist potencies between pre- and post-junctional .alpha.2-adrenoceptors but the absolute potencies of antagonists differed: antagonists were more potent prejunctionally. 3 In the human saphenous vein, the .alpha.2-adrenoceptor antagonist yohimbine had pre- and post-junctional actions over the same concentration range. 4 We have no evidence to suggest differences between pre- and post-junctional .alpha.2-adrenoceptors; differences in absolute antagonist potencies in the pithed rat may be due to non-equilibrium conditions.