[Various indicators of brain metabolism during hypoxia and hyperthermia].

Hypoxic, thermal and radiation tolerance of rats exposed to hypoxia and overheating for 4 to 22 days was measured. Activities of succinic dehydrogenase, lactate dehydrogenase and alkaline phosphomonoesterase as well as water content in the brain were examined biochemically and histochemically. Brain tolerance and metabolism varied in a phasic manner. Both specific and nonspecific adaptive reactions were identified. A direct correlation was established between hypoxic tolerance and aerobic oxidation decrease as well as enzyme-dependent transport in cerebral vascular walls. A relationship between CNS radiation tolerance and permeability of the blood-brain barrier was detected.