The effect of mild hypothermia on permanent focal ischemia in the rat

The effect of mild hypothermia on cerebral injury was evaluated in a rat model of permanent middle cerebral artery (MCA) and ipsilateral carotid artery occlusion. The MCA occlusion was performed in rats at temporalis muscle temperatures of 30 degrees C, 33 degrees C, 34.5 degrees C and 36.5 degrees C (n = 10, 8, 10, and 13, respectively). The animals were kept at the desired temperature for 1 hour and rewarmed to 36.5 degrees C. In a separate group of animals (n = 11), the temperature was decreased to 33 degrees C 1 hour after performing the arterial occlusion at normothermia. These animals were rewarmed to 36.5 degrees C after another hour with side by side controls (n = 9) kept at 36.5 degrees C throughout the experiment. Twenty-four hours after the MCA occlusion, rats were killed and the percentage of infarcted right hemisphere was determined in coronal brain sections with 2,3,5-triphenyltetrazolium chloride. The percentage of infarcted volume at 30 degrees C, 33 degrees C, and 34.5 degrees C (9.3 +/- 2.1%, 8.2 +/- 2.2%, and 8.4 +/- 2.2%) (SEM) was significantly smaller than at 36.5 degrees C (19.6 +/- 1.6%, P < 0.01). There were no significant differences between the hypothermic groups. When rats were cooled to 33 degrees C 1 hour after the arterial occlusion, the percentage of infarcted volume was also significantly smaller than the control group (8.0 +/- 1.8% vs. 17.4 +/- 2.1%) (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)