The effects of 3-week exercise training on the functions of peritoneal macrophages from BALB/c mice were investigated. Lipopolysaccharide (LPS)-stimulated nitric oxide (NO) and proinflammatory cytokine production in macrophages from trained mice was markedly higher than those from control mice. Meanwhile, exercise training decreased the steady state level of beta(2)-adrenergic receptor (beta(2)AR) mRNA in macrophages. Overexpression of beta(2)AR in the macrophage cell line RAW264 by transfecting with beta(2)AR cDNA suppressed NO synthase (NOS) II expression but dose not influenced proinflammatory cytokine expression. When expression of transfected beta(2)AR in RAWar cells was downregulated by a tetracycline repressor-regulated mammalian expression system, NOS II mRNA expression was significantly increased; this suggested that the changes in the beta(2)AR expression level in macrophages associated with exercise training play a role in the regulation of NO production following LPS stimulation. These findings indicate that exercise training improves macrophage innate immune function in a beta(2)AR-dependent and -independent manner.