Termination of responses to sympathetic nerve stimulation and to noradrenaline in a perfused arterial preparation: the role of neuronal and extraneuronal uptake.

Perfused branch vessels of bovine radial artery in vitro responded to sympathetic nerve stimulation and to noradrenaline added extralumenally and intralumenally with constrictions monitored as flow reductions. Cocaine and 17 beta-estradiol, inhibitors of neuronal and extraneuronal uptake, respectively, enhanced responses to exogenous noradrenaline given by either route. An analysis of response recovery rates, namely termination of action, revealed that the extraneuronal and neuronal uptake process each accounted for between 35 to 50% of the total inactivation capacity of the perfused neuroeffector system for noradrenaline. Responses to periarterial nerve stimulation over a 0.5 to 10 Hz frequency range, involving minimal to moderate flow reductions, were substantially magnified by cocaine and by 17 beta-estradiol. An analysis of response duration and recovery rates showed that extraneuronal processes were more significant than neuronal uptake in terminating noradrenergic transmitter action over the frequency band of 0.5 to 10 Hz.