Quantitation of high energy phosphate compounds and metabolic significance in the developing dog brain

The phosphate metabolites, PCr, ATP, ADP and inorganic phosphate (Pi), were quantitated in the brain of the newborn, neonatal, juvenile and adult dog to investigate the potential control mechanisms responsible for increased ATP demands during development. The concentrations of PCr and Pi were measured in vivo by MRS using the enzymatic-measured ATP as the internal standard. Phosphocreatine values increased during development from 2.08 mmol/kg wet weight in the 0-2 day newborn to 5.11 mmol/kg wet weight in the adult brain and paralleled the increases in the total creatine pool (PCr + Cr) from 4.12 to 10.05 mmol/kg wet weight. Brain ATP concentrations increased approximately 40% during postnatal development; however, when expressed as intracellular concentration, no increase in ATP was apparent due to the age-dependent decrease in extracellular space. The Pi concentration, estimated by MRS, increased significantly during postnatal development with a range of 1.78 to 2.52 mmol/kg wet wt, then decreased to 1.97 mmol/kg wet weight at adulthood. In those developmental stages where total Pi was measured enzymatically on freeze-clamped tissue, the NMR visible Pi comprised about 48 to 93% of the total, with the highest percentage being visible in the newborn brain. The intracellular pH decreased from 7.21 in the newborn to 7.10 in the adult. With development, the free ADP concentration, calculated from the components of the creatine kinase equilibrium, ranged from 27 to 34 microM. These values are close to the apparent in vitro Km of ADP for oxidative phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)