Role of nitric oxide on the central hemodynamic response to acute volume expansion in the pregnant rat, , ,

OBJECTIVES: Our hypothesis was that during pregnancy nitric oxide acts as mediator in the hemodynamic response to volume expansion. STUDY DESIGN: The study was performed on 12 rats on days 19 to 20 of pregnancy. Six rats were injected intravenously with hexamethonium bromide plus the inhibitor of nitric oxide synthase l-nitro-arginine methyl ester. For a control group, six rats were injected with hexamethonium bromide plus the l-nitro-arginine methyl ester vehicle. A volume expansion (1.2% body weight) was performed in both groups by intravenous infusion of bovine albumin (6%) solution. RESULTS: In the control group volume expansion induced a hyperdynamic circulation characterized by increased cardiac output, decreased total vascular resistance, and no change in arterial pressure; however, in the study group volume expansion induced a pressor response without hyperdynamic circulation. CONCLUSION: During pregnancy volume expansion induces a hyperdynamic circulatory state possibly mediated by nitric oxide release. A defect in the release of nitric oxide may be responsible for an inadequate hemodynamic response to volume expansion. (Am J Obstet Gynecol 1998;178:823-9.)