The gut: a cytokine-generating organ in systemic inflammation?

The aim of this study was to test the hypothesis that the gut is capable of becoming a cytokine-generating organ following either a lethal or nonlethal inflammatory insult. Adult male rats were given an intraperitoneal challenge with saline, or with a nonlethal (.1 mg/g) or LD50 (.5 mg/g) dose of zymosan. Mesenteric lymph nodes, efferent mesenteric lymph, liver, spleen, and blood (portal and systemic) were obtained at 2, 4, 6, 8, or 10 h post challenge. Organs, lymph, and blood were tested for bacterial translocation (BT); blood and lymph were assayed for tumor necrosis factor (TNF) and IL-6. After .1 mg/g zymosan, BT was limited to the mesenteric lymph node complex only; .5 mg/g zymosan promoted BT to blood, mesenteric lymph, and organs (p < .05 vs. control or .1 mg/g zymosan). The magnitude of portal bacteremia was greater than systemic bacteremia (p < .003). Serum TNF peaked at 2 h (p < .05 vs. control), and serum IL-6 peaked at 4-6 h (p < .05 vs. control) post zymosan challenge. Portal and systemic bioactivity was similar for either cytokine, and serum bioactivity did not correlate with zymosan dose. TNF bioactivity was increased in the mesenteric lymph at 2 h post challenge with .5 mg/g zymosan only (p < .05 vs. control or .1 mg/g zymosan). IL-6 bioactivity was increased in the mesenteric lymph at 4 through 10 h post zymosan challenge (p < .05 vs. control), but was similar with either dosage of zymosan. In conclusion, the gut may be capable of producing cytokines in response to an inflammatory stimulus, even in the absence of portal or systemic spread of bacteria. The magnitude of the cytokine response does not correlate with the magnitude of bacterial translocation.