Influence of profound hypothermia on the blood-brain barrier permeability during acute arterial hypertension.

In hypothermic rats with acute hypertension induced by intravenous injection of adrenalin, regional changes in blood-brain barrier permeability to macromolecules were investigated using Evans blue as indication. Evans blue albumin extravasation was determined as a macroscopic finding and a quantitative estimation with a spectrophotometer using homogenized brain to release the dye was also performed to evaluate the macroscopic findings. Five groups of rats were studied: Group I: normothermia + acute hypertension; Group II: hypothermia + acute hypertension; Group III: control hypothermia; Group IV: normothermia + hypotension; Group V: control normothermia. The rats were anaesthetized with diethyl-ether. Body temperature was lowered by submerging anaesthetized animals in an ice water bath. The colonic temperature was reduced to 20 +/- 1 degrees C. During adrenaline-induced acute hypertension the mean arterial blood pressure increased in both normothermic and hypothermic animals. Blood-brain barrier lesions were present in 40% of normothermic rats, and 60% of hypothermic rats after adrenaline-induced hypertension. Mean value for Evans blue dye in the whole brain was found to be 0.530 +/- 0.202 mg% in the normothermic rats and 0.752 +/- 0.256 mg% in the hypothermic rats during adrenaline-induced hypertension. This difference between normothermic and hypothermic rats was found to be statistically significant (P less than 0.01). Our results showed that the extravasation of Evans blue albumin was most pronounced in the brains of hypothermic rats compared to normothermic rats after adrenaline-induced acute hypertension.