RAT CULTURED ASTROCYTES RELEASE GUANINE-BASED PURINES IN BASAL CONDITIONS AND AFTER HYPOXIA HYPOGLYCEMIA/

Brain ischemia stimulates release from astrocytes of adenine-based pur ines, particularly adenosine, which is neuroprotective. Guanosine, whi ch has trophic properties that may aid recovery following neurological damage, is present in high local concentrations for several days afte r focal cerebral ischemia. We investigated whether guanine-based purin es, like their adenine-based counterparts, were released from astrocyt es and whether their release increased following hypoxia/hypoglycemia. HPLC analysis of culture medium of rat astrocytes showed spontaneous release of endogenous guanine-based purines at a higher rate than thei r adenine-based counterparts. The concentration of guanosine (approxim ate to 120 nM) and adenosine ( approximate to 43 nM) in the culture me dium remained constant, whereas concentrations of adenine and guanine nucleotides, particularly GMP, and their metabolites increased with ti me. Exposure of the cultures to hypoxia/hypoglycemia for 30 min increa sed the extracellular concentration of adenine-based purines by 2.5-fo ld and of guanine-based purines by 3.5-fold. Following hypoxia/hypogly cemia extracellular adenine nucleotide levels increased further. Adeno sine concentration increased, but not proportionally to nucleotide lev els. Accumulation of adenosine metabolites indicated it was rapidly me tabolized. Conversely, the concentrations of extracellular guanine-bas ed nucleotides remained elevated and the concentration of guanosine co ntinued to increase. These data indicate that astrocytes are a major s ource of guanine-based purines, the release of which is markedly incre ased following hypoxia/hypoglycemia, permitting them to exert neurotro phic effects. (C) 1999 Wiley-Liss, Inc.