EFFECTS OF ENDOTOXIN INJURY ON ENDOTHELIAL-CELL ADENOSINE METABOLISM

Adenosine is a potent autocoid that acts as a vasodilator and modulato r of inflammatory responses. Endothelial cells possess several mechani sms for altering circulating levels of adenosine and are capable of re lease of adenosine metabolites. We used cultured bovine aortic and mai n pulmonary arterial endothelial cells to determine whether endotoxin can alter adenosine uptake or release of adenosine metabolites. We fou nd that 24 hours, but not 6 hours, of incubation with endotoxin caused endothelial cell injury, as assessed by cell detachment and chromium 51 release. Despite this injury the extent of [H-3]adenosine uptake wa s unchanged. Using thin-layer chromatography to identify adenosine and its metabolites, we found that [3H]adenosine was primarily metabolize d into intracellular hypoxanthine and adenine nucleotides. After 1, 6, and 24 hours of incubation with endotoxin there was an increase in ex tracellular adenosine metabolites, which was accompanied by decreases in the level of intracellular adenosine 5'-triphosphate. The appearanc e of adenosine metabolites in culture supernatants was a more sensitiv e measure of endothelial cell injury than Cr-51 release or adherent ce ll number. The extracellular purine metabolite observed in response to endotoxin injury was mainly hypoxanthine. Our findings suggest that h ypoxanthine release is an early event in endotoxin-induced endothelial cell injury. Because hypoxanthine may act as a substrate for xanthine oxidase, resulting in toxic oxidant production, its release has the p otential of exacerbating vascular injury caused by endotoxin.