Phosphorus metabolites and intracellular pH in the brains of normal and small for gestational age infants investigated by magnetic resonance spectroscopy.

The brains of 30 normal preterm and term infants whose birth wt were appropriate for gestational age and 13 who were small for gestational age but healthy were studied by phosphorus magnetic resonance spectroscopy to determine values for metabolite concentration ratios and intracellular pH. In the AGA infants, phosphocreatine/inorganic orthophosphate increased between 28 and 42 wk of gestational plus postnatal age, suggesting a rise in the phosphorylation potential of brain tissue. At the same time, the concentration of phosphomonoester (mainly phosphoethanolamine) fell and that of phosphodiester (including phosphatidylethanolamine and phosphatidylcholine) increased. These changes reflected myelination and proliferation of membranes. Intracellular pH was approximately 7.1 and did not change with brain maturation. No differences were detected in these variables between the infants who were small for gestational age and those who were appropriate for gestational age.