The effects of adenosine analogues on the electrically-evoked acetylcholine(ACh) release and the influence of ischemia on the effects were studied in the rat hippocampus. Slices from the rat hippocampus were equilibrated with 0.1μM [<sup>3</sup>H]-choline and the release of the labelled product, [<sup>3</sup>H]-ACh, was evoked by electrical stimulation(3 Hz, 2 ms, 5 VCm<sub>γ</sub> and rectangular pulses for 2 min), and the influence of various agents on the evoked tritiumoutflow was investigated. Ischemia(10 min with 95% N<sub>2</sub> + 5% CO<sub>2</sub>) increased both the basal and evoked ACh release. These increases were abolished by glucose addition into the superfused medium, and they significantly inhibited either by 0.1 & 0.3μM TTX pretreatment or by removing Ca<sup>++</sup> in the medium. MK-801(1 ~ 10μM), a specific NMDA receptor antagonist, and glibenclamide (1μM), a K<sup>+</sup>-channel inhibitor, did not alter the evoked ACh release and nor did they affect the ischemia-induced increases In ACh release. However, polymyxin B(0.03 mg), a specific protein kinase C inhibitor, significantly inhibited the effects of ischemia on the evoked ACh release. Adenosine and N^6-cyclopentyladenosine decreased the ACh release in a dose dependent manner in ischemic condition, though the magnitude of inhibition was far less than those in normal(normoxic) condition. However, the treatment with 5μM DPCPX, a potent A<sub>1</sub>-adenosine receptor antagonist, potentiated the ischemia-effect. These results indicate that the evoked-ACh release is potentiated by ischemia, and this process being most probably mediated by protein kinase C, and that the decreased effect of ACh release mediated by A<sub>1</sub>-adenosine receptor is significantly inhibited in ischemic state.
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