Postischemic spontaneous hyperthermia and its effects in middle cerebral artery occlusion in the rat

This study examined the time course and effects of postischemic spontaneous hyperthermia after transient and permanent focal ischemia. Rats underwent a 90-min, 120-min, or permanent middle cerebral artery occlusion (MCAO). Bo dy temperatures started rising 15-20 min after MCAO and reached 39-40.5 deg rees C during the first hour. Sustained hyperthermia was observed during th e rest of the first 24 h. In another experiment, rats were subjected to the same interventions, but a normothermic body temperature was maintained. Sp ontaneous hyperthermia significantly increased the infarct volumes measured 48 h after MCAO in all groups. Reperfusion 2 h after the onset of ischemia was not beneficial in the hyperthermic animals in contrast to the normothe rmic group. We also examined the effect of spontaneous hyperthermia on the temporal progression of infarcted and penumbral areas 4, 12, or 48 h after MCAO. During spontaneous hyperthermia, penumbral areas became infarcted are as more rapidly, which was most expressed at 4 h. These findings demonstrat e that severe spontaneous hyperthermia can occur in rats after MCAO and tha t it not only increases the infarct volumes in both transient and permanent ischemia, but also accelerates the incorporation of penumbral areas into n ecrotic areas, which significantly decreases the window of opportunity for therapeutic interventions. (C) 2000 Academic Press.