title: The decrease in nonsplenic interleukin-6 (IL-6) production after splenectomy indicates the existence of a positive feedback loop of IL-6 production during endotoxemia in dogs.
abstract: The spleen is involved in endotoxin-induced interleukin-6 (IL-6) production. To quantitate the relative contribution of the spleen to endotoxin-induced IL-6 production, we studied the effect of endotoxin (1.0 microg/kg of body weight) in control dogs (n = 7) and splenectomized dogs (n = 7). Blood for analysis of tumor necrosis factor (TNF) and IL-6 was sampled from the femoral artery and the portal, hepatic, and splenic (only in controls) veins. Arterial plasma endotoxin and cortisol levels were also measured. Whole-body IL-6 production was calculated by a deconvolution technique. Splenic IL-6 production in control dogs was measured from splenic blood flow and arteriovenous concentration differences. Endotoxin levels were higher in splenectomized dogs (P < 0.05) because of a decreased distribution volume (P < 0.05) and decreased clearance of endotoxin (P < 0.05). Endotoxin-induced plasma IL-6 levels were decreased by approximately 75% in splenectomized dogs (P < 0.01), and whole-body IL-6 production rates were severalfold lower (median of 8.7 mg/4 h and range of 3.9 to 11.4 mg/4 h versus a median of 32.3 mg/4 h and a range of 22.7 to 70.2 mg/4 h) (P < 0.05). However, in control dogs splenic IL-6 production (0.6 +/- 0.2 mg/4 h) was only approximately 2% of whole-body IL-6 production. Plasma TNF levels increased in both groups (P < 0.01) but were not different between the groups. Plasma cortisol levels were slightly higher in splenectomized dogs than in control dogs (P < 0.05). In conclusion, splenectomy decreases the distribution volume and clearance rate of endotoxin. Splenectomy results in decreased endotoxin-induced IL-6 production, which is caused not by the absence of splenic IL-6 production, but by a decrease in nonsplenic IL-6 production. Therefore, the spleen is an important mediator in the complete activation of nonsplenic IL-6 production by endotoxin.
authors.affiliation: Department of Internal Medicine, Academic Medical Center, University of Amsterdam, The Netherlands.
authors.forename: H S
authors.initials: HS
authors.lastname: Moeniralam
authors.forename: W A
authors.initials: WA
authors.lastname: Bemelman
authors.forename: E
authors.initials: E
authors.lastname: Endert
authors.forename: R
authors.initials: R
authors.lastname: Koopmans
authors.forename: H P
authors.initials: HP
authors.lastname: Sauerwein
authors.forename: J A
authors.initials: JA
authors.lastname: Romijn
mesh_terms: D000818:Animals; D004285:Dogs; D019446:Endotoxemia / Q000276:immunology*; D004731:Endotoxins / Q000633:toxicity*; D005246:Feedback; D006439:Hemodynamics; D006854:Hydrocortisone / Q000097:blood; D015850:Interleukin-6 / Q000096:biosynthesis*; D008297:Male; D013156:Splenectomy; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
chemical_list: D004731:Endotoxins; D015850:Interleukin-6; D014409:Tumor Necrosis Factor-alpha; D006854:Hydrocortisone