Cardiovascular collapse with fatal drop in arterial blood pressure is a hallmark of gram-negative septic chock. In the present study we hypothesized a serial induction of cyclooxygenase-2 and activation of eNOS as responsible for the decrease in blood pressure, cardiac performance and vascular reactivity. The hypothesis was tested in chronically catheterized, conscious, freely moving wild type mice and COX-2-/- and eNOS-/- mice that were challenged with an intravenous bolus (2 mg/kg) of gram-negative lipopolysaccharide (LPS). In vitro, mice thoracic aorta rings were studied in a wire myograph. LPS caused a concomitant decrease in mean arterial blood pressure (MAP) and heart rate (HR) that was significant after 2-3h and sustained through the experiment (8h). The LPS-induced changes in MAP and HR were not different from control in COX-2-/- mice and in eNOS-/- mice. Intravenous infusion of a prostacyclin receptor (IP) antagonist, (BR5064, 0.1 mg/kg bolus followed by infusion at a rate of 0.005 mg/kg/h for 8 h), effectively blocked the hypotensive effect of an IP agonist (beraprost 20 µg/kg), but did not attenuate the LPS-induced decrease in MAP and HR. LPS decreased eNOS mRNA level in liver and aorta while iNOS mRNA was enhanced. LPS did not change eNOS protein level in liver in wt and COX-2 -/- mice. In aortic rings, LPS depressed contraction in response to the α1-adrenoceptor agonist phenylephrine. Inhibition of COX-2 (NS 398) or COX-2 deletion (COX-2-/-) had no effect on LPS-induced suppression of vascular reactivity. Endothelial removal did not change the effect of LPS. LPS-induced depression of vascular reactivity was prevented by incubation with the NOS-blocker, L-NAME in rings with and without endothelium. It its concluded that a serial coupling between COX-2 and eNOS is not necessary for LPS-induced systemic decrease in blood pressure and heart rate and suppression of vascular reactivity in mice whereas iNOS appears to be of central importance. COX-2 and eNOS do not appear as attractive therapeutic cardiovascular targets.