DIFFERENTIAL TEMPERATURE SENSITIVITY OF ISCHEMIA-INDUCED GLUTAMATE RELEASE AND EICOSANOID PRODUCTION IN RATS

The effect of mild and moderate hypothermia on ischemia-induced glutamate release and eicosanoid production was evaluated in WKY rats subjected to incomplete forebrain ischemia. Under isoflurane anesthesia, microdialysis probes were inserted into the hippocampus and caudate nucleus. In four groups of rats, the intraischemic temperature was maintained at either 38 degrees C (normothermia), 36 degrees C, 34 degrees C (mild hypothermia) and 30 degrees C (moderate hypothermia). In these groups, normothermia was restored immediately upon reperfusion. In two additional groups, both intra- and post-ischemic temperatures were maintained at either 34 degrees C or 30 degrees C. The levels of glutamate were measured in the dialysate collected during ischemia and the levers of TxB(2), 6-keto-PGF(1 alpha) and PGF(2 alpha) were measured in dialysate collected prior to and after ischemia. As expected, hypothermia reduced ischemia-induced glutamate release in both structures. However, the application of mild hypothermia did not attentuate post-ischemic levels of all eicosanoids measured. Moderate hyothermia (30 degrees C) attenuated the post-ischemic increase in the levels of PGF(2 alpha). The data suggest that the processes that lead to eicosanoid formation are less sensitive to temperature reduction than those that lead to glutamate release.