The efficiency of the neuronal re-uptake of noradrenaline-and the inhomogeneity of labelling of an incubated tissue.
In isolated vasa deferentia and atria of the rat, 90% of the spontaneous efflux of [(3)H]noradrenaline is subject to neuronal re-uptake, although the density of the adrenergic innervation is about seven times higher in the former than in the latter tissue. This surprising lack of any influence of the density of innervation on the efficiency of re-uptake is due to an inhomogeneous labelling of the tissue with [(3)H]noradrenaline. In the vas deferens the usual loading procedure results in two types of inhomogeneity: (1) autoradiography and an analysis of efflux indicate that a preferential labelling of surface-close varicosities takes place during loading. The consequences of this type of inhomogeneity are abolished by inhibition of uptake(1); desipramine enhances the spontaneous efflux much more for endogenous than for exogenous noradrenaline; (2) a second inhomogeneity involves a preferential labelling of the vesicles close to the surface of (labelled) varicosities. The consequences of this type of inhomogeneity of labelling are abolished by inhibition of vesicular uptake (by the reserpine-like compound Ro 4-1284). As a consequence of these inhomogeneities, the extent of neuronal re-uptake is much greater for endogenous than for exogenous noradrenaline.
Trendelenburg
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Institut für Pharmakologie und Toxikologie, Versbacher Str. 9, D-8700 Würzburg, F.R.G.
Schönfeld
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CL
Schömig
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E