The effect of timing of pneumoperitoneum on the inflammatory response

Background: We examined the effects of an identical period of pneumoperitoneum applied at three different time points after lipopolysaccharide (LPS) challenge. Two different insufflation gases were also compared. Methods: Male rats (n = 70) were injected intravenously with 1 mg/kg of LPS (time 0). The time relationship between a 1.5-h period of insufflation and initial LPS stimulation was the experimental variable. All rats were killed 6 h after injection. CO₂ and helium insufflation were investigated. Ten control rats received LPS only. Serum interleukin-6 (IL-6) levels were determined by enzyme-linked immunosorbent assay (ELISA). Hepatic expression of α₂-macroglobulin, β-fibrinogen, and metallothionein were measured by Northern blot analysis. Statistical analysis was performed using one-way analysis of variance (ANOVA). Results: Expression of α₂-macroglobulin mRNA was lower in CO₂ groups compared to the control group (p < 0.05 at time 120 and 270). β-Fibrinogen message was diminished in CO₂ 0 and 120 groups compared to control. Serum levels of IL-6 and expression of metallothionein mRNA did not show significant differences between groups. Conclusions: These findings suggest that CO₂ pneumoperitoneum downregulates the inflammatory response to LPS challenge. Start time of CO₂ insufflation does not appear to alter hepatic expression of acute phase genes. The mechanism of α₂-macroglobulin downregulation does not appear to be due to IL-6.