Stimulated nitric oxide release and nitric oxide sensitivity in forearm arterial vasculature during normotensive and preeclamptic pregnancy

Objective: We sought to determine whether the enhanced forearm vascular activity of nitric oxide during pregnancy and preeclampsia is associated with altered smooth muscle sensitivity to nitric oxide or with stimulated nitric oxide release. Study Design: Forearm blood flow responses to brachial artery infusion of glyceryl trinitrate (a nitric oxide donor), serotonin (an endothelium-dependent nitric oxide–mediated agonist), and ritodrine (a β-adrenergic receptor agonist) were studied in 10 nonpregnant women, 12 pregnant women, and 7 women with preeclampsia by means of strain-gauge plethysmography. Responses to each drug (maximum dilator response and the sum of the percentage of dilator responses to each drug) were compared by analysis of variance. Results: Compared with nonpregnant women, pregnant subjects showed reduced responses to serotonin (summary response, 117 ± 19 vs 221 ± 30; P< .05). Responses to serotonin were reduced in the group with preeclampsia compared with those in the nonpregnant group (summary response, 71 ± 28; P< .05) but did not differ from the responses in pregnant women. There were no differences between responses to glyceryl trinitrate and responses to ritodrine in any of the groups. Conclusion: Vascular smooth muscle sensitivity to nitric oxide is not altered in normal pregnancy or preeclampsia, but dilator responses to serotonin appear blunted. Alterations in serotonin receptor coupling to nitric oxide synthase, or a limitation of availability of the substrate for nitric oxide synthase (L -arginine) during pregnancy, could account for the reduction in stimulated nitric oxide release. (Am J Obstet Gynecol 1999;181:1479-85.)