Release of adenosine from rat hippocampal slices by nitric oxide donors

In the present study we have used perfused hippocampal slices to examine the hypothesis that nitric oxide (NO) can evoke the release of adenosine from nervous tissue. ATP stores were labeled by incubation with [3H]adenine. Electrical field stimulation at 5 Hz for 5 min evoked the release of 3H-purines, and this was enhanced by the NO donor S-nitroso-N-acetylpenicillamine (SNAP). Stimulation at 10 Hz for 15 min evoked a larger release of 3H-purines, which was enhanced in a concentration-dependent manner by both SNAP and sodium nitroprusside (SNP), with SNP being 100-fold less potent than SNAP. N-Acetylpenicillamine (N-AP) was without effect. SNAP had a markedly reduced, although significant, effect when given in the absence of field stimulation. Using HPLC it was found that SNAP enhanced the release of both endogenous and labeled adenosine in a concentration-dependent manner. At the highest concentration used (1 mM), SNAP increased electrically evoked release of endogenous adenosine 100-fold and unstimulated adenosine release eightfold. The ability of SNAP to enhance adenosine release was eliminated in the added presence of hemoglobin (10 microM), further supporting the proposal that the effects of SNAP were due to the liberation of NO. These data provide direct evidence that NO evokes a concentration-dependent release of adenosine from both stimulated and unstimulated nerves of the hippocampus. It is suggested that such NO-stimulated adenosine release may contribute to some of the reported effects of NO donors in the nervous system.