The neuropeptide cholecystokinin octapeptide (CCK-8) inhibits inflammation by downregulating the expression of proinflammatory cytokines, such as tumor necrosis factor alpha and interleukin (IL) 1beta during endotoxin shock. However, the signaling mechanism of CCK-8 action has not yet been clearly elucidated. In this study, we have examined the possible signaling pathways by which CCK-8 inhibits lipopolysaccharide (LPS)-induced IL-1beta production in rat pulmonary interstitial macrophages. In macrophages, LPS is known to activate p38 kinase, which, in turn, activates nuclear factor (NF)-kappaB to induce IL-1beta production. We found that the pretreatment of cells with CCK-8 blocked the LPS-induced p38 kinase, NF-kappaB activation, and IL-1beta production. Furthermore, CCK-8 treatment activated the cyclic adenosine monophosphate-protein kinase A signaling pathway and H-89 (a protein kinase A inhibitor), abrogated the inhibitory effects of CCK-8 on p38 kinase activation and NF-kappaB activation. In addition, we also demonstrate that the specific antagonist to CCK-1 receptor (CCK-1R) and CCK-2 receptor (CCK-2R) abrogate the CCK action, and that the effects of the antagonist specific to CCK-1R is more significant. These results suggest that these responses were mediated through CCK-1R and CCK-2R, and CCK-1R might be the major receptor responsible for the anti-inflammatory effect of CCK-8. Taken together, our results indicate that the stimulation of cyclic adenosine monophosphate-protein kinase A signaling pathway by CCK-8 through CCK-1R and CCK-2R inhibits the LPS-induced activation of p38 kinase and NF-kappaB to block the IL-1beta production in rat pulmonary interstitial macrophages.