Hemorrhagic shock causes severe depression of macrophage functions and is associated with increased susceptibility to sepsis. Because hemorrhagic shock and resuscitation encompasses several pathophysiological conditions, such as hypotension, low-flow conditions, hypoxia, and reperfusion injury, it remains unknown whether severe hypotension in the absence of blood loss has any adverse effects on macrophage functions. To study this, systemic arterial hypotension was induced in C3H/HeN mice for 15 min by intravenous infusion of sodium nitroprusside or ATP-MgCl2. Peritoneal macrophages (PM) was harvested 20 h later with lavage. Antigen presentation was measured by coculturing PM with the D10.G4.1 Th cell clone. Tumor necrosis factor (TNF), interleukin (IL)-6, IL-1, and prostaglandin (PG) E2 levels in supernatants of PM stimulated with lipopolysaccharide were measured with bioassays or radioimmunoassay. Systemic arterial hypotension resulted in a significant decrease of PM capacity to present antigen. Although the release of TNF, IL-6, and IL-1 by PM was unaltered after hypotension, PGE2 release by PM was significantly elevated compared with the control group. These data indicate that chemically induced systemic arterial hypotension without blood loss leads to a depression of antigen presentation, which may be caused by elevated release of the immunosuppressive eicosanoid PGE2.