Temporal sequence of pulmonary and systemic inflammatory responses to graded polymicrobial peritonitis in mice

Abstract

The lungs are the remote organ most commonly affected in human peritonitis. The major goals of this study were to define the dose- and time-dependent relationship between graded septic peritonitis and systemic and pulmonary inflammatory responses in mice. BALB/c mice were treated with intraperitoneal polymicrobial inoculi and sacrificed at 3, 12, and 24 h. The treatment protocol resulted in distinct groups of animals with respect to mortality rate, kinetics, and concentrations of a broad spectrum of pro- and anti-inflammatory endogenous mediators, intrapulmonary bacterial accumulation, and static lung compliance. In sublethally infected mice, pulmonary bacterial proliferation was controlled. Levels of monocyte chemoattractant protein-1 (MCP-1), interleukin-10, interleukin-6, granulocyte colony-stimulating factor (G-CSF), and tumor necrosis factor (TNF) in plasma were elevated 3 h after infection exclusively. At 3 h, MCP-1, gamma interferon, and TNF were detected in extracts of pulmonary tissue or in bronchoalveolar lavage (BAL) fluid. Static lung compliance (C(st)) was transiently decreased at 12 h. In contrast, in lethally infected mice pulmonary bacterial proliferation was not contained. Concentrations of MCP-1, G-CSF, and TNF in plasma were maximal at 24 h, as were pulmonary MCP-1 levels. Lung myeloperoxidase activity was increased at 3, 12, and 24 h. C(st) was reduced after 3 h and did not reach control values at 24 h. Pulmonary cyclooxygenase-2 mRNA and eicosanoids in BAL fluid and plasma were elevated at 3 and 24 h. This study shows that polymicrobial peritonitis in mice leads to dose-dependent systemic and pulmonary inflammation accompanied by a decrease in lung compliance.

FIG. 1

Survival of mice subjected to polymicrobial peritoneal infection: dose-response. Polymicrobial suspension was injected intraperitoneally at the doses indicated, and survival was monitored over 5 days. The data with doses of 1.5, 1, 0.5, 0.25, and 0.125 ml/kg are based on n = 3 animals per treatment group from one experiment.

FIG. 2

Plasma IL-10 (a), G-CSF (b), and IL-6 (c) concentrations 3, 12, and 24 h after induction of polymicrobial peritonitis in mice. Dosages are indicated as follows: ▵ (D), 1 ml/kg; ○ (C), 0.5 ml/kg; ◊ (B), 0.25 ml/kg, □ (A), 0.125 ml/kg; ⊕, controls. Each point in each panel is the mean ± SEM of measurements in four animals. ∗, P < 0.05; †, P < 0.01; ¶, P < 0.001 versus controls.

FIG. 3

MCP-1 concentrations in plasma (a), lung tissue (b), and lung lavage (c) 3, 12, and 24 h after induction of polymicrobial peritonitis in mice. Dosages are indicated as follows: ▵ (D), 1 ml/kg; ○ (C), 0.5 ml/kg; ◊ (B), 0.25 ml/kg; □ (A), 0.125 ml/kg; ⊕, controls. Each point in each panel is the mean ± SEM of measurements in four animals. ∗, P < 0.05; †, P < 0.01; ¶, P < 0.001 versus controls.

FIG. 4

TNF concentrations in plasma (a) and lung tissue (b) 3, 12, and 24 h after induction of polymicrobial peritonitis in mice. Dosages are indicated as follows: ▵ (D), 1 ml/kg; ○ (C), 0.5 ml/kg; ◊ (B), 0.25 ml/kg; □ (A), 0.125 ml/kg; ⊕, controls. Each point in each panel is the mean ± SEM of measurements in four animals. ∗, P < 0.05; †, P < 0.01; ¶, P < 0.001 versus controls.

FIG. 5

IFN-γ concentrations in lung tissue (a) and BAL fluid (b) 3, 12, and 24 h after induction of polymicrobial peritonitis in mice. Dosages are indicated as follows: ▵ (D), 1 ml/kg; ○ (C), 0.5 ml/kg; ◊ (B), 0.25 ml/kg; □ (A), 0.125 ml/kg; ⊕, controls. Each point in each panel is the mean ± SEM of measurements in four animals. ∗, P < 0.05; †, P < 0.01; ¶, P < 0.001 versus controls.

FIG. 6

RT-PCR analysis of lung tissue obtained from mice infected at 1 ml/kg at 3 h after induction of polymicrobial peritonitis (right lane). Shown are COX-1, COX-2, TXS, iNOS, and β-actin message. The left lane corresponds to control mice.

FIG. 7

Expression of mRNAs for COX-1 (a), COX-2 (b), TXS (c), and iNOS (d) in lungs 3, 12, and 24 h after induction of polymicrobial peritonitis in mice. □ (group D), dosage of 1 ml/kg; ◊, controls. Each point in each panel represents the mean ± SEM of measurements in four animals. The data are expressed as described in Materials and Methods.

FIG. 8

CFU (log 10/g of lung) of gram-positive (a) and gram-negative (b) bacteria 3, 12, and 24 h after induction of polymicrobial peritonitis in mice. Dosages are indicated as follows: ▵ (D), 1 ml/kg; ○ (C), 0.5 ml/kg; ◊ (B), 0.25 ml/kg; □ (A), 0.125 ml/kg; ⊕, controls. Each point in each panel is the mean ± SEM of measurements in four animals.

FIG. 9

Specific lung compliance (ml/cm of H₂O) 3, 12, and 24 h after induction of polymicrobial peritonitis in mice. Specific lung compliance was measured as described in Materials and Methods. Dosages are indicated as follows: ▵ (D), 1 ml/kg; ○ (C), 0.5 ml/kg; ◊ (B), 0.25 ml/kg; □ (A), 0.125 ml/kg; ⊕, controls. Each point in each panel is the mean ± SEM of measurements in four animals. ∗, P < 0.05; †, P < 0.01 versus controls.