Isoflurane attenuates carbogen-induced blood–brain barrier disruption independent of body temperature in mice and rats

Isoflurane protects the blood-brain barrier (BBB) against cerebral extravasation of Evans blue dye (EBD), a commonly used serum protein tracer, in animals subjected to BBB disruption. As such, it has been implicated as a therapeutic agent that can prevent brain edema and damage caused by a number of brain insults, including focal ischemia and subarachnoid hemorrhage. Recently, it has been shown that isoflurane inhibits the cerebral extravasation of EBD following ischemic stroke chiefly by inducing hypothermia, raising the intriguing possibility that isoflurane protected against other causes of BBB disruption also through hypothermia. To test this hypothesis, we subjected mice and rats to inhalation of 20-30% carbogen, an inducer of BBB disruption, in the presence or absence of isoflurane while measuring their rectal temperature. In mice, carbogen inhalation on its own decreased rectal temperature from 36.4 +/- 0.4 to 26.2 +/- 0.6 degrees C over a period of 60 minutes, and under this condition, isoflurane had no additional effect on body temperature. Nevertheless, isoflurane protected against carbogen-induced cerebral extravasation of EBD. In addition, when the body temperature was maintained in the normothermic range using an automated heating pad, isoflurane remained protective against cerebral extravasation of EBD. In rats, isoflurane also protected against cerebral extravasation of EBD, while having no effect on plasma pH, electrolyte concentrations, or osmolarity. In conclusion, isoflurane protected against BBB disruption caused by carbogen inhalation in mice and rats, but unlike isoflurane-mediated protection against ischemic BBB disruption, the effect could not be explained by anesthesia-induced hypothermia.