INTESTINAL PRODUCTION OF INTERLEUKIN-1-ALPHA DURING ENDOTOXEMIA IN THE MOUSE

Interleukin-1 (IL-1) may be involved in gut permeability to macromolecules and gut glutamine metabolism during endotoxemia. We developed a sensitive radioimmunoassay specific for mouse IL-1α (detection limit of 100 pg/ml, or 5 pM) and measured intestinal levels of IL-1α in response to endotoxin. CD- 1 mice (N = 190) were randomized to intraperitoneal (ip) or intravenous (iv) lipopolysaccharide (LPS) infusion (15 μg/g or 1.5 μg/g Escherichia coli 0111:B4 LPS) or saline. Mice were sacrificed at Time 0, 30 min, 1 hr, 2.5 hr, 4 hr, 6 hr, 12 hr, and 24 hr (3 mice/group/time point). Small bowel (SB) and large bowel (LB) were harvested and compared to liver. Duodenum, upper jejunum, mid-jejunum, terminal ileum, cecum, ascending colon, and sigmoid were analyzed in separate experiments. Tissues were frozen, weighed, and homogenized, the homogenates were centrifuged, and the supernates were assayed for immunoreactive IL-1α. IL-1α was expressed as pg/g wt ± SEM (lowest detectable amount = 1000 pg/g wet tissue (WT)). SB but not LB from normal controls had constitutively elevated levels of IL-1α (6177 ± 1640 pg/g WT). LPS ip or iv produced lethargy, diarrhea, and a dramatic elevation of IL-1α levels in both SB and LB. In SB, IL-1α was elevated compared to baseline at 1 hr (19201 ± 626 pg/g WT) and reached a fivefold maximal increase at 2.5 hr (31775 ± 503 pg/g WT) following 15 μg/g ip. Intestinal IL-1α levels were decreased at 4 hr (SB = 15830 ± 6138 pg/g WT) and returned to baseline levels at 24 hr. LB levels were twofold lower than SB levels and displayed a clearer dose response. Both SB and LB segments did not show a clear gradient of IL-1α expression. Intravenous LPS induced fivefold more IL-1α in SB and LB than ip LPS. Another group of mice (N = 80) was similarly treated, and the intestinal secretory response to LPS was studied. Intestinal IL-1α levels markedly correlated with intestinal mucus secretion in response to LPS, and the specific blockage of IL-1 by the IL-1 receptor antagonist attenuated this response. The rapid biphasic pattern of IL-1α (cell-associated IL-1) in SB and LB at early time points suggests an intestinal production and correlates with our previous demonstration of IL- 1α mRNA in SB by in situ hybridization. Furthermore, these data indicate that local (intrinsic) intestinal IL-1α has a role in sepsis-induced intestinal changes. © 1993 Academic Press, Inc.