Evidence for neuro‐effector transmission through postjunctional α2‐adrenoceptors in human saphenous vein

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Abstract
1 The effects of the α-adrenoceptor antagonist prazosin and the α2-adrenoceptor antagonist yohimbine were examined against stimulation-evoked contractions in human isolated saphenous veins. 2 The concentration of yohimbine producing 30% inhibition of stimulation-evoked contractions (IC30) was 13.2 nm, whereas the IC30 of prazosin was greater than 250 nm. 3 The inhibition of stimulation-evoked contractions by yohimbine was not prejunctionally mediated since yohimbine (0.01–0.1 μm) significantly potentiated the stimulation-evoked overflow of tritium in tissues pre-incubated with [3H]-noradrenaline. 4 The high potency of yohimbine and the low potency of prazosin indicate that neuro-effector transmission in human saphenous vein is mediated predominantly by postjunctional α2-adrenoceptors.

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