Adenosine released into the extracellular space by immunologic and nonimmunologic stimuli has been shown to regulate various immune functions. In this study we report that i.p. pretreatment of mice with CGS-21680 HCl (CGS), a selective agonist of A2 adenosine receptors, at 0.2 to 2 mg/kg caused an augmentation of plasma IL-10 levels induced by i.p. injection of LPS, but decreased plasma levels of LPS-induced TNF-alpha. 2-Chloro-N6-cyclopentyladenosine (CCPA), an agonist of A1 adenosine receptors, at 0.5 mg/kg diminished LPS-induced plasma TNF-alpha concentrations, but enhanced LPS-induced IL-10 levels only at the highest dose used (2 mg/kg). The specific A3 adenosine receptor agonist 1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-beta- D-ribofuranuronamide, at 0.2 and 0.5 mg/kg potentiated LPS-stimulated IL-10 production and inhibited LPS-induced TNF-alpha production. LPS-induced plasma nitrite and nitrate levels (the breakdown products of nitric oxide (NO)) were suppressed by CGS and CCPA. In the RAW 264.7 macrophage cell line, pretreatment of the cells with both CGS and CCPA inhibited LPS-induced IL-10, TNF-alpha, and NO production, each in a concentration-dependent manner. The inhibitory effect of these drugs on cytokine and NO production was associated with improved mitochondrial respiration. Neither CGS nor CCPA affected the LPS-induced nuclear translocation of transcription factor nuclear factor-kappaB in these cells. These results demonstrate that adenosine receptor stimulation differentially modulates the LPS-induced production of IL-10, TNF-alpha, and NO in vitro and in vivo. The increase in LPS-induced IL-10 production and suppression of LPS-induced TNF-alpha and NO production caused by adenosine receptor activation may explain some of the immunomodulatory actions of adenosine released in excess during inflammatory and/or ischemic insult.