38 METABOLISM IN CHANGED CEREBRAL ACTIVITY 



degrading or metabolizing the phosphates formed. Enzymes 

 capable of degrading energy-rich phosphates include acid and 

 alkaline phosphatases, adenosine triphosphatase and adenosine- 

 5 '-nucleotidase. The onset of maturation of the cortex is accom- 

 panied by a rapid and marked increase in the activity of adenosine 

 triphosphatase. In the rat activity increased rapidly from the low 

 level existing from birth to the 6th day of age, to the adult level in 

 15 days (Potter et al., 1945). In the guinea pig a similar increase 

 occurred from the 43rd day of gestation to birth (Flexner and 

 Flexner, 1948). In the chicken embryo adenosine triphosphatase of 

 the brain increased steadily from the 12th day of incubation 

 (Moog, 1947). Other enzymes probably related to the metabolism 

 of adenosine triphosphate include adenosine-5 '-nucleosidase 

 which in rat brain increases from a negligible quantity at birth to 

 the adult level within 120 days (Naidoo and Pratt, 1954). Measure- 

 ments upon the activity of creatine phosphokinase have not been 

 reported but are likely to show a similar trend. 



It must be admitted that the extent to which these enzymes 

 govern the quantities of their substrates in the brain in vivo, or 

 whether this is a sole or even a major function is not known. Some 

 indication of the manner in which they might act is provided by 

 studies with diphosphopyridine nucleotide and the corresponding 

 nucleotidase. In rat brain the quantity of diphosphopyridine 

 nucleotide remains relatively low at 0-18 /xmoles/g wet wt. until 

 about 10 days after birth. Between the tenth and twentieth day 

 quantities increase rapidly to the adult level of 0*3 /xmoles/g. At 

 the same time the activity of the nucleotidase increases thirtyfold. 

 This enzyme can be inhibited by nicotinamide (see also p. 88). 

 When given by intraperitoneal injection, nicotinamide, as a dose 

 of 500 mg/kg body wt., increased the quantities of cerebral 

 diphosphopyridine nucleotide by 30% in the eight day old rat and 

 by 50% in the 25-day-old animal (Burton, 1957). The nucleotidase 

 is thus implicated, as part of its action at least, with control of the 

 quantities of its suh .i ate. Such control is essential for the main- 

 tenance of the processes of respiration and phosphorylation and 

 forms the subject of separate discussions (see pp. 109-111, 159). 



Phospholipids 



Simultaneously with the development of enzyme systems 

 relating to energy metabolism there occur equally profound changes 



