Regulation of adrenomedullin secretion from cultured cells

Characterization of immunoreactive adrenomedullin (AM) secreted from cultured human vascular smooth muscle cells and 7 other cells indicates that AM is synthesized and secreted from all cultured cells we surveyed. The secretion rate of AM measured ranges from 0.001-6.83 fmol/10⁵ cells/h, and endothelial cells, vascular smooth muscle cells and fibroblasts generally secrete AM at high rates. Based on the results of regulation of AM secretion from vascular wall cells, fibroblasts, macrophages and other cells measured in this and previous studies, AM secretion is found to be generally stimulated by inflammatory cytokines, lipopolysaccharide (LPS) and hormones. Especially, vascular smooth muscle cells and fibroblasts elicited uniform and strong stimulatory responses of AM secretion to tumor necrosis factor (TNF), interleukin-1 (IL-1), LPS and glucocorticoid, but endothelial cells did not elicit such prominent responses. AM secretion of monocyte-macrophage was mainly regulated by the degree of differentiation into macrophage and activation by LPS and inflammatory cytokines including interferon-γ. The other examined cells showed weaker responses to LPS and IL-1. Although cultured cells may have been transformed as compared with those in the tissue, these data indicate that AM is widely synthesized and secreted from most of the cells in the body and functions as a local factor regulating inflammation and related reactions in addition to as a potent vasodilator. The responses of AM secretion to LPS and inflammatory cytokines suggest that fibroblasts, vascular smooth muscle cells and macrophage are the major sources of AM in the septic shock.