The effects of cytokines on intestinal glutamine metabolism were studied to gain further insight into the regulation of altered glutamine metabolism that occurs during severe infection. One hundred thirteen adult rats were given a single dose of interleukin-1 (IL-1, 50 μg/kg), tumor necrosis factor (TNF, 50 μg/kg or 150 μg/kg), or saline (controls), and flux studies were performed 4 or 12 hours later. Intestinal blood flow was not different between control and cytokine-treated animals at either time point. At the 4-hour time point, arterial glutamine fell by 16% to 21% in the cytokinetreated animals (p < 0.05); at the 12-hour time point, the arterial glutamine concentration had returned to normal. Intestinal glutamine extraction decreased in the animals treated with IL-1 at both time points (4 hours: 13% ± 1.3% in IL-1 versus 20% ± 1.6% in controls, p < 0.05; and 12 hours: 9% ± 2% in IL-1 versus 17% ± 2% in controls, p < 0.05). Consequently, net intestinal glutamine uptake fell in the animals treated with IL-1 at both time points (p < 0.05). Similarly, the activity of mucosal glutaminase, the principal enzyme of glutamine hydrolysis in the gut, fell by 50% in the 4hour study (6.1 ± 0.6 μmol/h/mg protein in IL-1 versus 9.6 ± 0.8 μmol/h/mg protein in controls, p < 0.01) and by 40% in the 12-hour study (5.4 ± 0.5 μmol/h/mg protein in IL-1 versus 8.8 ± 0.4 μmol/h/mg protein in controls, p < 0.05). Concomitant with the aforementioned decrease in gut glutamine metabolism was a 25% incidence of positive blood cultures for gram-negative organisms in IL-1 treated rats studied at the 12-hour time point (p = 0.05 versus controls). In the doses administered and at the time points studied, TNF had no effects on the parameters of gut glutamine metabolism examined. The results indicate that IL-1 is a potential mediator of the alterations in gut glutamine metabolism observed in sepsis and endotoxemia. © 1992.