Effect of repeated +Gz exposures on energy metabolism and some ion contents in brain tissues of rats

Background: It has been demonstrated that during +Gz exposure cerebral bloo d flow is significantly reduced, resulting in brain ischemia. In pilots, su ch conditions could recur several times during centrifuge training and comb at maneuvers and could possibly cause reversible change in brain energy met abolism. Hypothesis: In Fats there is an association between +10 Gz exposur e and the decreased brain metabolism, as indicated by decreased adenosine t riphosphate (ATP) and ATPase activity, and increased adenosine diphosphate (ADP) and lactate, etc. The aim of the present study was to examine the tim e course and recovery of brain energy metabolism, lactate, ATPase activity, Na+, K+, Ca2+ and water contents after three +10 Gr exposures in rats. Met hods: There were 64 male Sprague-Dawley rats that were restrained and place d on an animal centrifuge. They were divided into groups of 16. Control rat s were exposed to +1 Gz and experimental rats were exposed to +10 Gz three times each for 3 min at 30-min intervals. After being euthanized, rat brain s were removed 0 h, 1 h, or 6 h after the last centrifuge run. Brain sample s were analyzed for energy metabolism, lactate, Na+-K+-ATPase activity, wat er and electrolytes contents. Results: The cortical ATP content Na+-K+-ATPa se and lactate dehydrogenase (LDH) activities decreased significantly, wher eas the cortical ADP, adenosine monophosphate (AMP) and lactate contents in creased significantly 0 h after three +10 Gz exposures, as compared with th ose of central. The ATP, ADP, and AMP contents returned to their control le vels 1 h after the +10 Gz exposures, however, lactate content Na+-K+-ATPase and LDH activities delayed recovery 6 h after +10 Gz exposures. The cortic al KC content increased significantly 0 h and 1 h after +10 Gz exposures, a nd returned to the control level 6 h after +Clr exposures. Na+ and water co ntents increased significantly 1 h and 6 h after the +10 Gz exposures. Ther e was no significant change in Ca2+ content after +Gz exposures. Conclusion s: Three +10 Gz (3 min each) exposures were associated with transient depre ssion of brain metabolism as indicated by a decrease in ATP, Na+-K+-ATPase activity, and an accumulation of lactate, and disturbance of ion homeostasi s. It is suggested that a causal relationship might exist between repeated high +Gz exposures and brain metabolism.