Temporal regulation by adrenergic receptor stimulation of macrophage (Mφ)-derived tumor necrosis factor (TNF) production post-LPS challenge

Macrophage (Mφ) responsiveness can be regulated by various mediators, including those which emanate from, and mimic, the sympathetic nervous system. Whereas β-adrenergic agonists suppress, α₂-adrenergic agonists augment lipopolysaccharide (LPS)-stimulated tumor necrosis factor (TNF) production and gene expression. The susceptibility of Mφs to regulation of LPS-induced TNF production and mRNA accumulation was examined following β-adrenergic and α₂-adrenergic receptor activation at specific time points post-LPS challenge. Complete Freund's adjuvant-elicited murine Mφs were incubated with LPS (30 ng/ml) in the presence or absence of adrenergic agonists or antagonists. We assessed the susceptibility of immunologically-activated Mφs to adrenergic receptor regulation: a) during the 1 h delay in the production of TNF after LPS-stimulation, and b) during the rapid increase in TNF production which follows. Disparate responsiveness of Mφs to adrenergic drugs was observed during this time course of TNF production and TNF mRNA accumulation. In particular, while the concomitant addition of an α₂-adrenergic antagonist and LPS resulted in 45% suppression of TNF production, this selective blockade of α₂-adrenergic receptors on Mφs was equally effective throughout the first 45 min post-LPS challenge. After this initial period, the α₂-adrenergic receptor became progressively less responsive as demonstrated by the delayed addition of yohimbine (10^-5 M) post-LPS challenge. The addition of the selective α₂-adrenergic agonist UK-14304 (10^-7 M) to LPS-activated Mφs augmented TNF mRNA accumulation. However, this augmentation was even greater when the addition of the α₂-adrenergic agonist was delayed post-LPS challenge. It was also shown that the β-adrenergic agonist isoproterenol (10^-6 M) produced maximum suppression of TNF production within the first 1.5 h post-LPS challenge. Suppression by isoproterenol (10^-6 M) of TNF mRNA accumulation occurred throughout the 2-h period assessed post-LPS stimulation of Mφs. The decline in isoproterenol-induced regulation was accompanied by an elevation in β₂-adrenergic receptor mRNA accumulation. Furthermore, suppression of TNF production induced by a maximum concentration of isoproterenol was observed at various LPS concentrations (0.001-1000 ng/ml), although this was not as pronounced a suppression as demonstrated for dibutyryl cAMP. These results demonstrate that the susceptibility of Mφs to adrenergic receptor regulation changes throughout the time period necessary for gene activation and ultimate release of TNF. Thus, the production of TNF during LPS-dependent disease states may be regulated by adrenergic mediators throughout different temporal windows, better explaining the role played by the nervous system.