Autoregulation of Endogenous Epinephrine Release via Presynaptic Adrenoceptors in the Rat Hypothalamic Slice1

High-K (30 mM)-evoked release of endogenous epinephrine in hypothalamic slices from three rats in the presence of tetrodo-toxin, 3 x iO M, was measured by high-performance liquid chromatography wfth an eleCtrOchemiCal detector. Spontaneous and evoked release of epinephrmne was markedly reduced, when rats were pretreated with 2,3-dichloro-a-methylbenzylamine, an inhibitor of phenylethanolamine N-methyltransferase, the enzyme catalyzing the formation of epinephnne from norepnephrine, 80 mg/kg i.p., before decapitation. The amount of epinephnne re-leased during the resting state was lower by a factor of approx-imately 2 orders than that of norepinephrine and dopamine but was consistently higher than the limit of the sensitivity of this assay system, 0.1 to 0.3 pmol. The evoked release of epineph-rine was Ca dependent. Isoproterenol, 10 M to 10 M, dos