BRIEF HYPOXIC STRESS DOWN-REGULATES E-COLI-INDUCED IL-1-ALPHA AND IL-1-BETA GENE-EXPRESSION IN PERFUSED LIVER

Hepatic cytokine gene expression is independently stimulated by circul ating microbial products and reductions in the cellular O-2 supply. Al though these stimuli occur sequentially after gram-negative bacteremia , it is unknown whether their interplay augments production of interle ukin (IL)-1 by the liver. We studied the effects of intraportal Escher ichia coli (EC) bacteremia and secondary constant-flow hypoxia (P-O2, similar to 46 Torr for 30 min) on IL-1 alpha and IL-1 beta gene expres sion in ex situ buffer-perfused rat livers over 180 min (n = 67). At t = 0, normoxic EC and normal saline (NS) controls received 10(9) live EC serotype 055:B5 and 0.9% NaCl, respectively; in livers subjected to EC + hypoxia-reoxygenation (H/R) and NS + H/R, hypoxia began 0.5 h af ter EC or NS and was followed by 120 min of reoxygenation. Portal and hepatic venous perfusates were serially analyzed for bacterial colony- forming units, O-2 uptake, and aspartate aminotransferase. At 60 min ( peak hypoxia) and 180 min, cDNAs for IL-1 alpha and IL-1 beta were hyb ridized to whole liver RNA, and IL-1 beta protein levels in venous per fusates were assessed. Intrahepatic levels of reduced glutathione (GSH ) were measured as an index of oxidative stress. Compared with normoxi c EC, IL-1 alpha transcripts decreased at 180 min in EC + H/R livers ( P < 0.0001) as did IL-1 beta mRNA (P < 0.05), despite similar EC clear ance, GSH levels, posthypoxic O-2 uptake, and aspartate aminotransfera se release. Hepatic secretion of IL-1 beta likewise fell in EC + H/R v s. EC controls (P < 0.005). Prostaglandin H synthase-2 (COX-2) message accumulation was not enhanced by H/R, and indomethacin did not revers e H/R-mediated suppression of IL-1 production. In contrast, H/R-relate d falls in EC-induced IL-1 beta expression were reversed by allopurino l or catalase. Thus brief hypoxic stress of the liver causing neither GSH depletion nor functional impairment downregulates postbacteremic I L-1 expression by a mechanism involving Oa radicals but not cyclooxyge nase metabolites.