Factors influencing the uptake of noradrenaline by subcellular particles in homogenates of rat brain

A preparation of granules obtained from rat brain by differential centrifugation has been investigated for characteristics of release and uptake of catecholamines. Activation and fluorescence spectra obtained from chromatographically isolated extracts of such granules indicated that noradrenaline is the predominant endogenous catecholamine. The rate of release of this endogenous noradrenaline varied directly with temperature of incubation. When the brain granules were incubated with exogenously added noradrenaline, uptake varied directly with the external concentration of the amine, with partial saturation appearing at concentrations beyond 200 mμg noradrenaline/ml incubation medium. Partial depletion of noradrenaline from brain granules by incubation at 37° did not alter the capacity of the granules to take up exogenous noradrenaline. Greater actual uptake of exogenous noradrenaline by the granules occurred at 37° than at 4°, even though total uptake was less at 37°. Administration of reserpine to the rats markedly decreased endogenous levels of noradrenaline in the brain granules. Although granules from reserpine-treated animals continued to demonstrate an uptake of exogenous noradrenaline, the total quantity taken up was markedly below that in control preparations. Neither dinitrophenol nor iodoacetic acid altered the uptake of exogenous noradrenaline by the brain granules.