Brain Adenosine and Transmitter Amino Acid Release from the Ischemic Rat Cerebral Cortex: Effects of the Adenosine Deaminase Inhibitor Deoxycoformycin

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Abstract
The effects of a potent adenosine deaminase inhibitor, deoxycoformycin, on purine and amino acid neuro‐transmitter release from the ischemic rat cerebral cortex were studied with the cortical cup technique. Cerebral ischemia (20 min) was elicited by four‐vessel occlusion. Purine and amino acid releases were compared from control ischemic animals and deoxycoformycin‐pretreated ischemic rats. Ischemia enhanced the release of glutamate, aspartate, and γ‐aminobutyric acid into cortical perfusates. The levels of adenosine, inosine, hypoxanthine, and xanthine in the same perfusates were also elevated during and following ischemia. Deoxycoformycin (500 μ/kg) enhanced ischemia‐evoked release of adenosine, indicating a marked rise in the adenosine content of the interstitial fluid of the cerebral cortex. Inosine, hypoxanthine, and xanthine levels were depressed by deoxycoformycin. Deoxycoformycin pretreatment failed to alter the pattern of amino acid neurotransmitter release from the cerebral cortex in comparison with that observed in control ischemic animals. The failure of deoxycoformycin to attenuate amino acid neurotransmitter release, even though it markedly enhanced adenosine levels in the extracellular space, implies that the amino acid release during ischemia occurs via an adenosine‐insensitive mechanism. Inhibition of excitotoxic amino acid release is unlikely to be responsible for the cerebroprotective actions of deoxycoformycin in the ischemic brain.