Lipopolysaccharide Exposure Modifies High Tidal Volume Ventilation-induced Proinflammatory Mediator Expression in Newborn Rat Lungs

Infection/inflammation and mechanical ventilation have both independently been shown to increase cytokine/chemokine levels in lung tissue and blood samples of premature patients. Little is known about the combined effect of systemic inflammation and mechanical ventilation on cytokine expression in the lung. We tested whether pre-existing inflammation induced by lipopolysaccharide (LPS) exposure would modify cytokine/chemokine response in newborn rat lungs to high tidal volume ventilation (HTVV). Newborn rats were randomly assigned to four groups: groups I and II (saline); groups III and IV: 3 mg/kg LPS. Groups II and IV were 24h later subjected to 3h of ventilation with a tidal volume of 25 mL/kg. HTVV alone increased IL-1beta, IL-6 and the chemokine (C-X-C motif) ligand 2 (CXCL2) mRNA expression. Although the cytokine response to LPS alone had disappeared after 24 h, the combination of LPS pretreatment and HTVV significantly increased the expression of IL-6 and IL-1beta mRNA when compared with HTVV alone. TNF-alpha expression was increased neither by HTVV alone nor in combination with LPS. IL-6 protein content in bronchoalveolar lavage increased due to the combined treatment. Thus, a subtle pre-existing inflammation combined with HTVV amplifies the proinflammatory cytokine/chemokine expression in the newborn rat lung compared with HTVV alone.