Measurement of cerebral reactive hyperemia at the initial post-ischemia reperfusion stage under normothermia and moderate hypothermia in rats

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Inhibition of the initial events occurring immediately after ischemia-reperfusion seems to be beneficial for reducing the extent of subsequent chronic neuronal cell injury. We investigated the effects of moderate hypothermia (32°C) commencing 30 min before ischemia on reactive hyperemia by measuring cerebral blood flow (CBF) with a laser-Doppler flowmeter at the initial ischemia-reperfusion stage (60 min) following 10 min of global cerebral ischemia in rats. In normothermia, CBF was increased to approximately 240% and decreased thereafter, although it remained at approximately 150% after 60 min of ischemia-reperfusion. In contrast, hypothermia increased CBF to more than 270% after ischemia-reperfusion, then recovered to the basal level within 30 min. The period of reactive hyperemia under normothermia tended to be shortened by pre-administration of an NMDA antagonist, in a manner similar to hypothermia. Furthermore, hypothermia inhibited the presence of cells with caspase-3-like immunoreactivity in the hippocampal CA1 sector after 8 h of ischemia-reperfusion. Our findings indicate that hypothermia tends to shorten the period of reactive hyperemia during the initial ischemia-reperfusion stage. This phenomenon may be partly associated with activation of NMDA receptors and a beneficial effect of hypothermia in resisting progression of the neurotoxic cascade in the first 8 h after ischemia-reperfusion. (J Oral Sci 51, 615-621, 2009)