Differential labelling of intraneuronal noradrenaline stores with different concentrations of (-)-3H-noradrenaline.

Isolated preparations of the rabbit vas deferens were incubated with (--)-(3)H-nor- adrenaline. A preferential release of (3)H-noradrenaline was demonstrated after electrical stimulation of the intramural nerves in those tissues labelled with 10 ng/ml (3)H-noradrenaline. There was no preferential release of (3)H-noradrenaline when the vasa were initially labelled with 100 ng/ml (3)H-noradrenaline. It is concluded that low concentrations of (3)H-noradrenaline do not mix homogeneously with the total tissue store but enter a small easily releasable store.