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 DE SIGN: 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 eater. For a control group, six rats were injected with hexamethonium bromid e 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 increas ed cardiac output, decreased total vascular resistance, and no change in arterial pressure; however, in the study group volume expansion ind uced a presser response without hyperdynamic circulation. CONCLUSION: During pregnancy volume expansion induces a hyperdynamic circulatory s tate possibly mediated by nitric oxide release. A defect in the releas e of nitric oxide may be responsible for an inadequate hemodynamic res ponse to volume expansion.