Effect of orotic acid on the metabolism of cerebral cortical astrocytes during hypoxia and reoxygenation: an NMR spectroscopy study.

Astrocytes were incubated under normoxic or hypoxic conditions in Dulbecco's minimum essential medium containing [2-13C]acetate, unlabeled glucose and in some cases orotic acid, an intermediate in pyrimidine biosynthesis. After 12 hr the medium was replaced by fresh medium without drug and incubation was continued for 17 hr in a normal oxygen atmosphere (reoxygenation). Thereafter, medium was removed, cell extracts were prepared, and metabolism in the treatment group was compared to the untreated hypoxia group and to control. 13C and 1H NMR spectra revealed that 13C enrichment in citrate and glutamine C-4 in the initial medium were increased in the presence of orotic acid, compared to the untreated hypoxia group but lower than control. The drug increased acetate utilization during hypoxia to normoxic levels. Thus it appears that the treatment group had a more active mitochondrial metabolism, which was also reflected in higher intracellular uridine diphosphoryl sugars and ADP concentrations. Glutamine labeling was increased in the cell extracts in the presence of orotic acid. Thus it appears that, in the presence of the pyrimidine nucleotide precursor, astrocytes are capable of normal metabolism during hypoxia which might have implications for neuronal survival during low oxygen insults, since neurons are dependent on astrocyte produced precursors for their neurotransmitter synthesis.