RELEASE OF NORADRENALINE FROM CAT SPLEEN SLICES BY POTASSIUM

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Abstract
1 When cat spleen slices were exposed to a potassium-enriched (140mM) Krebs solution, 367 ± 31 ng g−1 5 min−1 of noradrenaline (NA) was released into the bathing medium. 2 Phenylephrine and clonidine (10−7 to 10−3M) did not significantly modify the potassium-evoked NA release; acetylcholine decreased it in a dose-dependent manner. 3 Phenoxybenzamine increased NA release by 50% but phentolamine did not alter it; high concentrations of this drug greatly decreased NA release. Cocaine increased the NA release by about 30%. 4 It is suggested that the failure of sympathomimetic amines to depress, and of α-adrenoceptor blocking agents to enhance the release of NA by high potassium concentrations may be related to prolonged depolarization of the nerve terminals, which may desensitize presynaptic α-receptors. The fact that the same drugs are able to modify NA release during electrical nerve stimulation may be ascribed to the much shorter periods of depolarization occurring under these conditions.