To determine whether ANG II as well as mechanical stress affect the production of tumor necrosis factor (TNF) in the heart, neonatal rat cardiac myocytes and fibroblasts were cultured separately and treated for 6 h with ANG II, lipopolysaccharide (LPS), or cyclic mechanical stretch. LPS induced the production of TNF in cardiac myocytes and fibroblasts. However, TNF synthesis in fibroblasts was 20- to 40-fold higher than in myocytes. ANG II (≥10⁻⁸ M) and mechanical stretch stimulated the production of TNF in cardiac fibroblasts but not in myocytes. Furthermore, both ANG II and LPS increased the expression of TNF-α mRNA in cardiac fibroblasts. Isoproterenol inhibited both LPS- and ANG II-induced production of TNF in cardiac fibroblasts with increasing intracellular cAMP level. Moreover, both isoproterenol and dibutyryl cAMP inhibited LPS-induced TNF-α mRNA expression. Thus activation of the renin-angiotensin system, as well as mechanical stress, can stimulate production of TNF in cardiac fibroblasts. Furthermore, β-adrenergic receptors may be responsible for the regulation of TNF synthesis at the transcriptional level by elevating intracellular cAMP.