Intestinal Production of Interleukin-1α during Endotoxemia in the Mouse

Abstract 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 p M ) 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, midjejunum, 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.