Comparison of the effects of phenoxybenzamine and uptake blockade on noradrenaline efflux from rabbit ear arteries evoked by field stimulation and propagated nerve impulses.

1. A comparison has been made of the effects of blockade of prejunctional alpha-adrenoreceptors and blockade of transmitter noradrenaline uptake in segments of rabbit ear arteries subjected to field stimulation or neuronally propagated impulses. 2. The relationship between evoked release and frequency of stimulation differed in artery segments subjected to field stimulation and those receiving propagated nerve impulses. However, the effectiveness of phenoxybenzamine in increasing stimulation-induced efflux of radioactivity decreased as the frequency of stimulation increased in artery segments subjected to either field stimulation or neuronally propagated impulses. 3. Blockade of neuronal and extraneuronal uptake had no effect on evoked efflux from field-stimulated artery segments but it did produce a marked and significant enhancement of release evoked by propagated nerve impulses.