Hyperbaric and normobaric reoxygenation of hypoxic rat brain slices--impact on purine nucleotides and cell viability.

Hyperbaric oxygen treatment has been suggested as able to reduce hypoxia induced neuronal damage. The aim of the study was to compare the impact of different reoxygenation strategies on early metabolical (purine nucleotide content determined by HPLC) and morphological changes (index of cell injury after celestine blue/acid fuchsin staining) of hypoxically damaged rat neocortical brain slices. For this purpose slices (300μm and 900μm) were subjected to either 5 or 30min of hypoxia by gassing the incubation medium with nitrogen. During the following reoxygenation period treatment groups were administered either 100% oxygen (O) or room air (A) at normobaric (1atm absolute, NB-O; NB-A) or hyperbaric (2.5atm absolute, HB-O; HB-A) conditions. After 5min of hypoxia, both HB-O and NB-O led to a complete nucleotide status restoration (ATP/ADP; GTP/GDP) in 300μm slices. However, reoxygenation after 30min of hypoxia was less effective, irrespective of the oxygen pressure. Furthermore, administering hyperbaric room air resulted in no significant posthypoxic nucleotide recovery. In 900μm slices, both control incubation as well as 30min of hypoxia resulted in significantly lower trinucleotide and higher dinucleotide levels compared to 300μm slices. While there was no significant difference between HB-O and NB-O on the nucleotide status, morphological evaluation revealed a better recovery of the index of cell injury (profoundly injured/intact cell-ratio) in the HB-O group. Conclusively, the posthypoxic recovery of metabolical characteristics was dependent on the duration of hypoxia and slice thickness, but not on the reoxygenation pressure. A clear restorative effect on purine nucleotides was found only in early-administered HB-O as well as NB-O in contrast to room air treated slices. However, these pressure independent metabolic changes were morphologically accompanied by a significantly improved index of cell injury, indicating a possible neuroprotective role of HB-O in early posthypoxic reoxygenation.