Role of nitric oxide in cardiovascular responses to endotoxemia in neonatal lambs

To determine whether systemic cardiovascular responses to gram-negative end otoxemia are mediated by nitric oxide, we evaluated time-dependent changes in contractility and hemodynamics in a neonatal sheep model subjected to ni tric oxide synthesis inhibition with L-Name (NW-nitro-L-arginine methyl est er). Four groups were studied: control (C), endotoxin (E), endotoxin L-Name where the nitric oxide synthase inhibitor was given prior to endotoxin (EL N), and a control L-Name group pretreated with L-Name (CLN). The contractil ity, measured as end-systolic elastance (Ees), increased transiently in the E group and then returned to baseline. In contrast, Ees declined over time in the ELN group. In terms of peripheral hemodynamics, both the E and ELN groups demonstrated significant progressive decreases in blood pressure and vascular resistance. The results of this study suggest that nitric oxide c ontributes to the newborn contractile response of the heart to endotoxin, b ut does not appear to mediate the systemic vascular relaxation response.