The extent of neuronal re-uptake of 3H-noradrenaline in isolated vasa deferentia and atria of the rat

Abstract

After pretreatment of rats with reserpine and pargyline (to inhibit vesicular uptake and monoamine oxidase, respectively) and after inhibition of catechol-O-methyl transferase (by U-0521) and in calcium-free solution, the adrenergic neurones of isolated vasa deferentia and atria were loaded with 3H-noradrenaline. The spontaneous efflux of 3H-noradrenaline and 3H-dihydroxyphenylglycol was determined, as well as the steady-state effect of two concentrations of desipramine. On the basis of a mathematical model of the adrenergic nerve ending, fractional rates (FR = rate of flux divided by tissue tritium content) were calculated for unidirectional outward diffusion, for outward transport and for neuronal re-uptake (all for 3H-noradrenaline). Although the density of adrenergic innervation is lower in atria than in vasa deferentia, neuronal re-uptake amounted to about 90% of the spontaneous efflux of 3H-noradrenaline in both tissues. While the FR for unidirectional outward diffusion was virtually the same in both tissues, the FR for outward transport of 3H-noradrenaline was more than three times higher in atria than in vasa deferentia. There is, as yet, no explanation for this pronounced difference.