GLUCOCORTICOIDS REGULATE INTESTINAL GLUTAMINE-SYNTHETASE GENE-EXPRESSION IN ENDOTOXEMIA

Purpose: Although glutamine is required to maintain gut mucosal metabo lism and function, intestinal glutamine uptake from the gut lumen and from the bloodstream is decreased during sepsis. We hypothesized that endogenous mucosal glutamine biosynthesis is increased during endotoxe mia, and we attempted to define the ''stress'' mediators that regulate the activity of small intestinal glutamine synthetase (GS), the princ ipal enzyme of de novo glutamine biosynthesis in the gut. Methods: Adu lt rats received Escherichia coli lipopolysaccharide (LPS) (7.5 mg/kg intraperitoneally), RU 38486 (a glucocorticoid antagonist; 10 mg/kg by gavage) 2 hours prior to LPS administration, antibody to tumor necros is factor (TNF) (4 mg/kg intraperitoneally) prior to LPS administratio n, or ketorolac tromethamine (a prostaglandin synthesis inhibitor; 1 m g/kg intraperitoneally) followed by LPS administration. Mucosal GS act ivity was assayed 12 hours after LPS administration. In a separate set of studies, cultured intestinal mucosal cells (Caco-2) were exposed t o LPS, interleukin 1 (IL-1), IL-6, TNF-alpha, interferon-gamma, prosta glandin E(2), or dexamethasone. Twelve hours later, GS activity was as sayed and messenger RNA was extracted. The GS transcripts were labeled with a GS complementary DNA probe radiolabeled with phosphorus 32, we re quantitated by phosphoimaging, and were normalized to beta-actin. R esults: In vivo LPS treatment increased mucosal GS activity by 250%. P retreatment with antibody to TNF or ketorolac did not inhibit the LPS- induced increase in mucosal GS, whereas pretreatment with RU 38486 att enuated the increase in gut GS activity by 60%. Lipopolysaccharide, IL -I, IL-6, TNF-alpha, gamma-interferon, and prostaglandin E(2) did not increase GS activity in Caco-2 cells, whereas dexamethasone increased GS activity and messenger RNA 2.5-fold and threefold, respectively. Th ese data indicate that cytokines and prostaglandins (prostaglandin E(2 )) do not regulate mucosal GS expression during endotoxemia. Glucocort icoids, however, stimulate GS gene expression directly. Conclusions: T his hormonally mediated response may support de novo mucosal GS during septic states when uptake of glutamine from the lumen and blood is de creased.