TNF-alpha is an important pro-inflammatory mediator that influences host defense against infection and cancer. Previous examinations of TNF-alpha release and synthesis within the context of age have provided conflicting data, as both increased and decreased TNF-alpha synthesis have been described in aged populations. The present study was designed to reevaluate TNF-alpha production and synthesis in primary cultured peritoneal macrophages of young and 18-month-old rats. We were also interested in the link between the production of this cytokine and other important mediators, such as prostaglandin I(2) (PGI(2)) and nitric oxide (NO) in these rats. Primary cultured peritoneal macrophages of rat were stimulated with 1.0 microg/ml of lipopolysaccharide (LPS) for 12 h. The level of TNF-alpha protein in culture supernatant was measured by enzyme-linked-immunosorbent-assay (ELISA), and TNF-alpha mRNA production was assessed by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). At the same time, the levels of NO and PGI(2) were measured. Macrophages from 18-month-old rats produced more TNF-alpha protein, PGI(2) and TNF-alpha mRNA than those from the young rats (2 month). There was no difference in NO production of macrophages between 18-month-old and young rats. The results demonstrate that TNF-alpha and PGI(2) production by rat macrophages increase with age. The results also suggest that NO might not contribute to the increased TNF-alpha production in 18-month-old rat macrophages.