INDUCTION OF ADRENOMEDULLIN MESSENGER-RNA AND PROTEIN BY LIPOPOLYSACCHARIDE AND PACLITAXEL (TAXOL) IN MURINE MACROPHAGES

Lipopolysaccharide (LPS), a potent inflammatory stimulus derived from the outer membrane of gramnegative bacteria, has been implicated in se ptic shock. Plasma levels of adrenomedullin (Ah/I), a potent vasorelax ant, are increased in septic shock and possibly contribute to the char acteristic hypotension. As macrophages play a central role in the host response to LPS, we studied AM production by LPS-stimulated macrophag es. When peritoneal exudate macrophages from C3H/OuJ mice were treated with protein-free LPS (100 ng/ml) or the LPS mimetic paclitaxel (Taxo l; 35 mu M), an similar to 10-fold increase in steady-state AM mRNA le vels was observed, which peaked between 2 and 4 h. A three- to fourfol d maximum increase in the levels of immunoreactive AM protein was dete cted after 6 to 8 h of stimulation. While LPS-hyporesponsive C3H/HeJ m acrophages failed to respond to protein-free LPS with an increase in s teady-state AM mRNA levels, increased levels were observed after stimu lation of these cells with a protein-rich (butanol-extracted) LPS prep aration. In addition, increased AM mRNA was observed following treatme nt of either C3H/OuJ or C3H/HeJ macrophages with soluble Toxoplasma go ndii tachyzoite antigen or the synthetic flavone analog 5,6-dimethylxa nthenone-4-acetic acid. Gamma interferon also stimulated C3H/OuJ macro phages to express increased AM mRNA levels yet was inhibitory in the p resence of LPS or paclitaxel. In vivo, mice challenged intraperitoneal ly with 25 mu g of LPS exhibited increased AM mRNA levels in the lungs , liver, and spleen; the greatest increase (>50-fold) was observed in the liver and lungs. Thus, AM is produced, by murine macrophages, and furthermore, LPS induces AM mRNA in vivo in a number of tissues. These data support a possible role for AM in the pathophysiology of sepsis and septic shock.