Effect of Directly and Indirectly Acting Sympathomimetic Amines on Adrenergic Transmitter Granules

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Abstract
The actions of various sympathomimetic amines on release and reuptake of noradrenaline (NA)1in splenic nerve granules during incubation in phosphate buffer have been studied.The effect on the basic release rate was studied in the absence of NA in the medium.The degree of reuptake was determined with the aid of dl‐3H‐NA.Tyramine (TA) 10‐7–10‐4M causes a moderate direct releasing effect of NA from nerve granules which reaches a constant level within 10 min at 20d̀.In 10‐5–10‐3M concentration TA inhibits the reuptake of NA in granules.After previous loading of granules with radioactive NA, addition of TA to the incubation medium releases NA with apporoximately the same specific activity as that in the total store.Tritiated TA is taken up in nerve granules to a small extent, approximately corresponding to the direct release of NA.The releasing action of TA is blocked by reserpine 10‐5M.phenoxybenzamine 3 X 10‐4M and desmethylimipramine 3 X 10‐4M.Phenethylamine and amphetamine have a strong direct releasing effect and a moderate effect on reuptake of NA in granules.Ephedrine and mephentermine slightly retard NA release and inhibit NA reuptake at 3 X 10‐4M.Dopamine competitively inhibits reuptake of NA in granules.The effects of amines on release and reuptake in granules differ markedly from those exerted on the overall uptake of NA in perfused organs.

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