The effects and interactions of 4β-phorbol 12,13-dibutyrate(PDB) and polymyxin B(PMB) with adenosine on the electrically-evoked norepinephrine (NE) release were studied in the rat hippocampus. Slices from the rat hippocampus were equilibrated with <sup>3</sup>H-noradrenaline and the release of the labelled product, <sup>3</sup>H-NE, which evoked by electrical stimulation(3 Hz, 2 ms, 5 VCm<sup>-1</sup>, rectangular pulses) was measured. PDB(0.3 ~ 10μM), a selective protein kinase C(PKC) activator, increased the evoked NE release in a dose related fashion while increasing the basal rate of release. And the effects of 1μM PDB were significantly inhibited by 0.3μM tetrodotoxin(TTX) pretreatment or Ca<sup>++</sup>-free medium. PMB(0.03 ~ 1 mg), a specific PKC inhibitor, decreased the NE release in a dose dependent manner while increasing the basal rate of release. Adenosine (1 ~ 10μM) decreased the NE release without changing the basal rate of release, and this effect was significantly inhibited by 8-cyclopentyl-1,3-dipropylxanthine(2μM), a selective A<sub>1</sub>-receptor antagonist, treatment. Also, adenosine effects were significantly inhibited by PDB-and PMB-pretreatment. These results suggest that the PKC plays a role in the NE release in the rat hippocampus and might be participated in a post-receptor mechanism of the A<sub>1</sub>-adenosine receptor.
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