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 levels of TxB2, 6-keto-PGF1 alpha and PGF2 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 attenuate post-ischemic levels of all eicosanoids measured. Moderate hypothermia (30 degrees C) attenuated the post-ischemic increase in the levels of PGF2 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.