The neuroprotective effects of ethyl pyruvate (EP), a stable derivative of pyruvate, on energy metabolism of rat brain exposed to ischemia-reperfusion stress were investigated by (31)P-nuclear magnetic resonance ((31)P-NMR) spectroscopy. Recovery level of phosphocreatine after ischemia was significantly greater when superfused with artificial cerebrospinal fluid (ACSF) with 2 mM EP than when superfused with ACSF without EP. EP was neuroprotective against ischemia only when administered before the ischemic exposure. Intracellular pH during ischemia was less acidic when superfused ahead of time with EP. EP did not show neuroprotective effects in neuron-rich slices pretreated with 100 microM fluorocitrate, a selective glial poison. It was suggested that both the administration of EP before ischemic exposure and the presence of astrocytes are required for EP to exert neuroprotective effects. We suggest the potential involvement of multiple mechanisms of action, such as less acidic intracellular pH, glial production of lactate, and radical scavenging ability.