Tumour necrosis factor-α (TNF-α) is a central immunoregulatory cytokine involved in septic responses during bacterial infection (Damas et al. 1997, Van Dullemen et al. 1997). Previous studies in our laboratory have shown that this cytokine is able to inhibit L-leucine intestinal absorption (Abad et al. 2002). In this work, D-fructose transport was studied in rabbit jejunum (obtained from a rabbit killed by a blow to the head) from control and treated (intravenously with TNF-α 2 µg (kg body weight)^-1, 1 h 30 min) animals.

We studied the sugar transport using three experimental methods: (a) tissue accumulation (incubations were for 3 min, at 37 °C, under 95 % O₂-5 % CO₂ bubbling, the measurements were expressed as micromoles of D-fructose per millilitre of cell water), (b) transepithelial flux in Ussing-type chambers (the bathing solutions on the mucosal and serosal surfaces of the tissue were maintained at 37 °C, under 95 % O₂-5 % CO₂ bubbling, the results are expressed as micromoles of D-fructose per cm² per hour) and (c) brush-border membrane vesicles (BBMV) were prepared using the Mg²⁺, EGTA precipitation method (Hauser et al. 1980) with minor modifications (Brot-Laroche et al. 1986). All results are expressed as means ± S.E.M. Means were compared using a one-way analisis of variance (ANOVA). Significant differences (P < 0.05) were compared using a Student’s unpaired two-tailed t test. Handling, equipment and killing of animals was in accordance with the European Council Legislation 86/609/EEC concerning experimental animal protection.

The results have shown that TNF-α decreases significantly (about 30 %) the accumulation (control 2.50 ± 0.05, TNF-α 2.12 ± 0.01), the mucosal-to-serosal transepithelial flux (control 0.41 ± 0.01, TNF-α 0.28 ± 0.02) and the uptake across brush-border membrane vesicles of D-fructose at different times. This inhibition could be related to the TNF-α secretagogue effect on the gut because the intracellular tissue water was affected. Likewise, the absence of chloride ion in the incubation medium removed, in part (about 90 %), the cytokine inhibition. To explain this inhibition, the density of the D-fructose transporter GLUT5 was analysed by Western blot. GLUT5 levels were lower in TNF-α-treated animals, indicating a significant reduction in the expression of GLUT5 protein and, therefore, in the transport capacity.

To sum up, the inhibition of D-fructose intestinal absorption by intravenous administration of TNF-α could be mainly produced by a reduction in the number of GLUT5 transporters and, at least in part, by the secretagogue action of this endotoxin on the gut.

The rabbit polyclonal antibody GLUT5 was kindly provided by Dr E. Brot-Laroche (INSERM U505, Paris, France). This work was supported by grants from CICYT (SGPN Y+D) AGL 2000-1228 and University of Zaragoza, Spain.