Effect of adrenoreceptors on endotoxin-induced cytokines and lipid peroxidation in lung explants

Lung tissue may be an important source of systemic inflammation associated with sepsis and the acute respiratory distress syndrome (ARDS). An ex vivo model of freshly explanted lung tissue in culture was developed to evaluate the ability of lipopolysaccharide (LPS) to directly stimulate lung tissues under conditions where indirect mechanisms such as recruitment of blood-derived inflammatory cells could not be implicated. Under control conditions, lung explants produced a high level of macrophage inflammatory protein-2 (MIP-2). Eight hours after LPS challenge, there were marked increases in the production of tumor necrosis factor-alpha: (TNF-alpha) from 0.18 +/- 0.04 to 4.13 +/- 0.23 ng/ml/g tissue (p < 0.05), MIP-2 from 60.0 +/- 7.4 to 165.6 +/- 10.3 ng/ml/g tissue (p < 0.05), and tissue lipid peroxidation (malonaldehyde from 27.6 +/- 2.5 to 48.4 +/- 17.5 mu M/g tissue; and 4-hydroxyalkenal from 34.0 +/- 3.0 to 59.7 +/- 18.8 mu M/g tissue, both p < 0.05) from lung explants. Treatment with the beta-adrenoreceptor agonist isoproterenol (1 ng/ml) attenuated LPS-induced release of TNF-alpha and lipid peroxidation in association with an increase in intracellular cAMP levels. The adenylate cyclase activator, forskolin, also inhibited LPS-induced changes in TNF-alpha and lipid peroxidation. In conclusion, increasing intracellular levels of cAMP through beta-adrenoreceptor activation can attenuate the acute inflammatory response induced in the lung by LPS. LPS did not significantly impair the beta-adrenoreceptor reactivity in lung explants. Lung explants allow for the quantitative assessment of pulmonary inflammatory responses independent of influences from the circulation, and thus may be a useful ex vivo model to investigate cellular and molecular mechanisms of lung injury.