Although an individual's genetic makeup is a major determinant of their muscle mass, other influences, such as hormones, cytokines, nutrition, and exercise can also modulate muscle size. Interleukin-6 is an important inflammatory cytokine. Mice that over-express IL-6 fail to thrive and/or have reduced skeletal muscle mass. The purpose of the present study was to determine whether the stress hormone epinephrine increases inflammatory cytokine expression in skeletal muscle and muscle cells. Infusion of epinephrine in vivo for 2 h increased IL-6 protein (15-fold) and mRNA (40- fold) in skeletal muscle, but not in liver. Epinephrine had a similar effect in C2C12 muscle cells where the hormone increased IL-6 protein and mRNA in a dose- and time-dependent manner. Epinephrine-stimulated IL-6 expression was attenuated by the -adrenergic receptor antagonist phentolamine and completely blocked by either the _1/2 adrenergic receptor antagonist propranalol or the ₂ antagonist ICI118551. The transcriptional inhibitor DRB and the synthetic glucocorticoid dexamethasone also blocked epinephrine-induced IL-6. SP600125 (a Jun-N-terminal kinase inhibitor) and SB202190 (a p38 MAP kinase inhibitor) completely blocked epinephrine-induced IL-6 synthesis. Endotoxin and epinephrine given together had a synergistic affect on IL-6 mRNA and protein expression. Trichostatin A (a histone deacetylase inhibitor) blocked both endotoxin- and epinephrine- induced IL-6 expression. These data suggest that epinephrine induces IL-6 synthesis in skeletal muscle in vivo and myocytes in vitro. Epinephrine utilizes predominantly B₂-adrenergic receptors to stimulate IL-6 synthesis. Endotoxin and epinephrine synergize to increase IL-6 mRNA expression. Optimal IL-6 synthesis may require both stress kinase and histone deacetylase activity.