The aim of this study was to investigate the effects of IL-10, a cell permeable analogue of cyclic AMP, dibutyryl-cAMP (db-cAMP), modulators of intracellular cyclic AMP such as phosphodiesterase (PDE) inhibitors and a beta 2-adrenoceptor agonist, salmeterol, on pulmonary inflammation following acute lung injury induced by endotoxin exposure in rats. Pulmonary inflammation was induced in adult Wistar rats by a 60-min exposure to endotoxin (lipopolysaccharide, LPS, 100 micrograms/mL). 4 h later bronchoalveolar lavage (BAL) was performed. The PDE inhibitors, rolipram (3 and 5 mg/kg) and theophylline (30 and 100 mg/kg) inhibited neutrophil recruitment, TNF-alpha release and cellular activation in BAL. Salmeterol (0.5 mg/mL) and IL-10 (0.1 microgram) only inhibit TNF-alpha increase in the BAL fluid and db-AMPc (2.5 micrograms/rat) was ineffective. The present data show that the selective PDE4 inhibitor, rolipram, and the non-selective PDE inhibitor, theophylline, markedly reduced the pulmonary inflammation associated with acute lung injury in the rat. These effects may be mediated in part by IL-10 rather than by cyclic AMP, as demonstrated by the potent inhibitory activity of exogenous IL-10 on the increase in TNF-alpha release in BAL fluid of rats exposed to LPS.