Contribution of nonendothelial nitric oxide to altered rat uterine resistance artery serotonin reactivity during pregnancy

Objective: The aims of this study were to evaluate the effects of pregnancy on the serotonin reactivity of the mesometrial arteries and to assess the relative contribution of endothelial and smooth muscle cells to the overall effect. Study Design: Arteries were obtained from nonpregnant (n = 20) and late pregnant (n = 28) Sprague-Dawley rats and were cannulated in the chamber of an arteriograph. Changes in lumen diameter were measured by a video dimension analyzer. Statistical analysis used 2-way analysis of variance, followed by Bonferroni test. Results: Intact vessels from late pregnant versus nonpregnant animals were significantly less sensitive to the constrictor effects of serotonin at concentrations <100 nmol/L. A role for endothelial nitric oxide was indicated on the basis of the effects of denudation and Nω-nitro-L-arginine. Furthermore, the additional effect of Nω-nitro-L-arginine in denuded vessels from pregnant animals suggests that another, nonendothelial source of nitric oxide also contributes to the effect. Conclusion: Pregnancy significantly decreases uterine resistance artery sensitivity to serotonin. This difference in sensitivity is due to the enhanced production of nitric oxide by endothelial cells and, most likely, by vascular smooth muscle. (Am J Obstet Gynecol 2002;187:463-8.)