Adrenomedullin expression and its effects on cytokine response of rat macrophages to lipopolysaccharide

Abstract

BACKGROUND: Adrenomedullin (AM) is a potent vasorelaxant peptide that plays important roles in inflammation. AM derived from circulating immune cells, such as monocytes and macrophages, is one of the largest sources of AM which arises in the inflammatory process. To assess the functions of AM in inflammation, we studied the temporal changes in AM production and its effect on cytokine response of rat macrophages activated by lipopolysaccharide (LPS). METHOD: Rat macrophages (NR8383) were activated by LPS in the absence and presence of AM at 1 ng/ml to 1 mg/ml. Concentrations of AM, proinflammatory cytokines (TNF-a, IL-1b and IL-6), and macrophage migration inhibitory factor (MIF) in the culture media were measured at 1, 3, 6, and 24 h after LPS/AM stimulation. Total RNA was extracted from the cells and mRNA expression was quantified by RT-PCR. RESULTS: Stimulation of LPS increased AM secretion and AM mRNA expression of the macrophages by 4- to 15-fold at 3–24 h after LPS-stimulation. AM at 1 mg/ml markedly increased IL-6 secretion from both non-stimulated and LPS-stimulated macrophages at 6–24 h, by 1- to 10-fold. AM also increased initial secretion of IL-1b and MIF from both non-stimulated and LPS-stimulated cells at 1–6 h, but it reduced the subsequent production of IL-1b and MIF from LPS-stimulated cells by 10% and 22%, respectively, at 24 h. However, AM reduced production of TNF-a from LPS-stimulated cells at 1–24 h by 35–66%. CONCLUSION: Our results suggest that AM modulates cytokine production and MIF secretion from rat macrophages and its role in the inflammatory process changes with time after onset of the inflammatory challenge.