Creatine and nucleoside triphosphates in rat cerebral gray and white matter.

In vivo localized nuclear magnetic resonance spectroscopy has shown three-fold higher phosphocreatine/nucleoside triphosphate (PCr/NTP) ratios in cerebral white compared to gray matter. To interpret these results, total creatine (Cr) and ATP concentrations were measured enzymatically in samples taken from rapidly frozen rat cerebral cortex and corpus callosum. Total Cr (PCr plus Cr) and ATP concentrations were the same in the two regions. High performance liquid chromatography showed similar concentrations of total NTP in the two regions. These results suggest that higher in vivo PCr/NTP ratios in white compared to gray matter may be due to a higher PCr/Cr ratio in white matter and/or higher percentages of non-adenine mono- or diphosphate nucleotides in gray matter.