SYSTEMIC HEMODYNAMICS AND REGIONAL BLOOD-FLOW DURING CHRONIC NITRIC-OXIDE SYNTHESIS INHIBITION IN PREGNANT RATS

Pregnancy-induced hypertension in women is associated with severe vaso constriction and reductions in organ blood flow and cardiac output. Re cent studies have indicated that nitric oxide (NO) synthesis inhibitio n during mid to late gestation in pregnant rats results in severe hype rtension and proteinuria. The purpose of this study was to determine t he systemic hemodynamic and regional blood flow alterations associated with chronic NO synthesis inhibition in the pregnant rat. The study w as conducted in four groups of rats: virgin rats (n=6), pregnant rats (n=10), virgin rats treated with L-NAME (n=6), and pregnant rats treat ed with L-NAME (n=11). Rats were treated with L-NAME in drinking water at a dose of 1 mg/d for a week starting from day 13 of gestation in p regnant rats or an equivalent time for virgins. Mean arterial pressure (MAP), cardiac output, total peripheral resistance (TPR), and regiona l flows were measured by tracing radiolabeled microspheres in consciou s rats. Pregnant rats that were given L-NAME showed significantly high er MAP (137+/-6 versus 96+/-2 mm Hg), higher TPR (5.08+/-0.58 versus 2 .90+/-0.44 mm Hg/mL/min/100 g), and lower cardiac output (87.4+/-8.4 v ersus 113.3+/-11.1 mL/min) than pregnant controls. Chronic NO synthesi s inhibition decreased the renal blood flow in pregnant rats at a sign ificantly greater magnitude than in virgin rats. significant reduction s in regional blood flow to the heart, lungs, Liver, diaphragm, and sk eletal muscles were also observed in pregnant rats treated with L-NAME . The results of this study indicate that NO may play a role in mediat ing the alterations in systemic hemodynamics and regional blood flow i n late pregnant rats.