METABOLIC AND BIOSYNTHETIC ALTERATIONS IN CULTURED ASTROCYTES EXPOSEDTO HYPOXIA REOXYGENATION

To investigate the astrocyte response to hypoxia/reoxygenation, as a m odel relevant to the pathogenesis of ischemic injury, cultured rat ast rocytes were exposed to hypoxia. On restoration of astrocytes to normo xia, there was a dramatic increase in protein synthesis within 3 h, an d sodium dodecyl sulfate-polyacrylamide gel electrophoresis of metabol ically labeled astrocyte lysates showed multiple induced bands on fluo rograms. Levels of cellular ATP declined during the first 3 h of reoxy genation and the concentration of AMP increased to almost-equal-to 3.6 nmol/mg of protein within 1 h of reoxygenation. Reoxygenated astrocyt es generated oxygen free radicals early after replacement into ambient air, and addition of diphenyliodonium, an NADPH oxidase inhibitor, di minished the generation of free radicals as well as the induction of s everal bands on fluorogram. Although addition of cycloheximide on reox ygenation resulted in inhibition of both astrocyte protein synthesis a nd accumulation of cellular AMP, it caused cell death within 6 h, sugg esting the importance of protein synthesis in adaptation of hypoxic as trocytes to reoxygenation. Potential physiologic significance of biosy nthetic products of astrocytes in hypoxia/reoxygenation was suggested by the recovery of glutamate uptake. These results indicate that the a strocyte response to hypoxia/reoxygenation includes generation of oxyg en free radicals and de novo synthesis of products that influence cell viability and function in ischemia.