NITRIC OXIDE-MEDIATED VASODILATION IN HUMAN-PREGNANCY

The maternal circulation vasodilates during pregnancy. We investigated the contribution of nitric oxide to this vasodilatation. Using venous occlusion plethysmography, we measured the effect of nitric oxide syn thase inhibition on hand blood flow during human pregnancy. We compare d the response to a brachial artery infusion of the nitric oxide synth ase inhibitor NG-monomethyl-L-arginine (L-NMMA) with the response to n orepinephrine in three groups of women: nonpregnant, early pregnant (9 -15 wk), and late pregnant (36-41 wk). Basal hand blood flow increased significantly during late pregnancy compared with nonpregnant and ear ly pregnant subjects (P = 0.007). L-NMMA produced a greater reduction in hand blood flow in both pregnant groups compared with nonpregnant c ontrols (P = 0.0003). Norepinephrine produced an attenuated response i n late pregnancy compared with nonpregnant and early pregnant women (P = 0.0029). If other vascular beds respond in the same way as the hand , the gestational increase in vasoconstrictor response to L-NMMA that we observed implicates increased generation of nitric oxide in the fal l of peripheral vascular resistance during healthy human pregnancy.