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Endogenous norepinephrine regulates tumor necrosis factor-alpha production from macrophages in vitro
R N Spengler1, S W Chensue, D A Giacherio
1Department of Pathology, S.U.N.Y. at Buffalo, School of Medicine and Biomedical Sciences, NY 14214.
Abstract:
Evidence for the extraneuronal accumulation of norepinephrine has been demonstrated to occur in macrophage (M phi), yet the physiologic role of this system remains undefined. We have assessed the response of murine peritoneal M phi to adrenergic antagonists. We have also defined a physiologic role of a M phi-associated pool of the nonspecific adrenergic agonist norepinephrine. We investigated the constitutive involvement of alpha-adrenergic and beta-adrenergic receptors in LPS-induced TNF-alpha production. CFA-elicited M phis were incubated with LPS (1 microgram/ml) in the presence or absence of adrenergic agonists and/or antagonists. Although stimulation of alpha-adrenergic receptors increased TNF production and gene expression, beta-adrenergic receptors decreased it. Interestingly, when adrenergic antagonists along with LPS alone were added to M phi, they generated the response opposite to that produced by their suitable agonist, suggesting a role for endogenous norepinephrine in M phi. Thus, although alpha 2-adrenergic antagonists attenuated TNF production, beta-adrenergic antagonists augmented TNF expression in a concentration-dependent manner. Norepinephrine and epinephrine were found in M phi as determined by HPLC and LPS stimulation induced a significant decrease in their content. M phis were also incubated with LPS or medium only, washed, and then challenged 12 h later with LPS. When given a second LPS stimulation, M phis were found to have an increased response to alpha 2-adrenergic agonists and decreased response to alpha 2-adrenergic antagonists. Therefore, M phi-associated norepinephrine appears to regulate LPS-induced TNF production in an autocrine fashion.
Insights
Macrophages store norepinephrine, influencing tumor necrosis factor-alpha (TNF-alpha) production. Alpha-adrenergic stimulation increases TNF-alpha, while beta-adrenergic stimulation decreases it, suggesting an autocrine role for macrophage-associated norepinephrine.
Area of Science:
- Immunology
- Neuroscience
- Pharmacology
Background:
- Macrophages (M phi) accumulate extraneuronal norepinephrine, but its physiological role is unclear.
- Adrenergic receptors are present on macrophages and may influence immune responses.
Purpose of the Study:
- To investigate the role of macrophage-associated norepinephrine in regulating lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha (TNF-alpha) production.
- To define the physiological function of the M phi-associated norepinephrine pool.
Main Methods:
- Murine peritoneal macrophages were stimulated with LPS in the presence or absence of adrenergic agonists and antagonists.
- High-performance liquid chromatography (HPLC) was used to quantify norepinephrine and epinephrine in M phi.
- Macrophage responses to secondary LPS stimulation after initial LPS exposure were assessed.
Main Results:
- Alpha-adrenergic receptor stimulation increased TNF-alpha production and gene expression, while beta-adrenergic receptors decreased it.
- Adrenergic antagonists produced opposite effects to their agonists, indicating a role for endogenous norepinephrine.
- Macrophage-associated norepinephrine levels decreased upon LPS stimulation.
- Pre-exposure to LPS altered M phi responses to adrenergic agonists and antagonists.
Conclusions:
- Macrophage-associated norepinephrine plays an autocrine role in modulating LPS-induced TNF-alpha production.
- Alpha-adrenergic signaling enhances TNF-alpha, whereas beta-adrenergic signaling suppresses it.
- Endogenous norepinephrine within macrophages influences their inflammatory response.