50 METABOLISM IN CHANGED CEREBRAL ACTIVITY 



23-35% in arterial blood and 15-22% in the sagittal sinus. The 

 arterio-venous difference also decreased indicating an impaired 

 oxygen uptake by the brain. Changes were complete within 15 min 

 and were not increased by prolonging the hypoxia to 1 hr. The 

 effects noted were due to lack of oxygen since the levels of glucose 

 in the blood were consistently higher than normal. 



These effects are apparently not obtained provided sufficient 

 time has been allowed for the animal to become acclimatized to the 

 lower oxygen tension. Albaum et al. (1953) exposed rats, in 

 stepwise progression, to oxygen tensions representing increased 

 altitudes until, over a period of weeks, a final tension equivalent to 

 20,000 ft was obtained. At this tension blood haemoglobin was 

 markedly increased. Animals were maintained at this altitude for 

 7 months, conditions under which unacclimatized adult rats die 

 within a few hours (Britton and Kline, 1945) and were then anaes- 

 thetized and brought back to ground level before freezing in liquid 

 nitrogen. No differences from normal were detected in the 

 quantities of cerebral phosphocreatine, adenosine triphosphate or 

 inorganic phosphate. Although anaesthesia and maintenance for 

 a short period at normal oxygen tensions might have obliterated any 

 temporary change in the quantities of these phosphates it would 

 appear that they were metabolized at normal rates in the acclima- 

 tized rats. Thus, injection of radioactive phosphate 1 hr before 

 freezing failed to reveal any differences in the rate of incorporation 

 of radioactivity into the phosphorus of adenosine triphosphate 

 between the normal controls and acclimatized animals. Com- 

 parable experiments as regards phosphate turnover have not been 

 reported with animals rendered anoxic as in the experiments of 

 Gurdjian et al. Reducing the oxygen content of the inspired air to 

 4-2% was without effect upon the quantities of adenosine triphos- 

 phate in rabbit brain (Stone et al., 1941) though phosphocreatine 

 had decreased. 



Changes in adenosine triphosphate occur in complete anoxia 

 and are accompanied by corresponding increases in the quantities 

 of adenosine diphosphate and adenylic acid (Gurdjian et al, 1949; 

 Albaum et al., 1953; Doring and Gerlach, 1957; Gerlach et al, 

 1958). Even so, levels remain high until phosphocreatine has 

 completely disappeared (Table 8). Such decreases are always 

 accompanied by increases in the quantities of inorganic phosphate, 

 the increase in which greatly exceeds the amount made available 



