Endothelium-dependent relaxation of human resistance arteries in pregnancy

Objective: Reduced peripheral vascular resistance is an integral component of vascular adaptation in pregnancy. The precise mediators of the reduced resistance are unknown, however, and are often assessed by indirect means. In this study we investigated endothelium-dependent relaxation directly by examining acetylcholine-mediated relaxation in small arteries dissected from the subcutaneous fat layer undergoing biopsy at the time of gynecologic surgery and cesarean section. Study Design: By means of a small vessel myograph we measured tension in resistance arteries of normal pregnant (n = 22) and nonpregnant (n = 10) women and assessed the contributions of vasodilatory prostanoids and endothelium-derived relaxing factor on endothelium-dependent relaxation, as elicited by acetylcholine (1 nmol/L to 10 μmol/L) after precontraction with 3 μmol/L norepinephrine. Results: Endothelium-dependent relaxation was similar in arteries of pregnant and nonpregnant women. Sodium nitroprusside-induced relaxation was similar in arteries of pregnant and nonpregnant women. Conclusion: This study fails to demonstrate any increase in acetylcholine-induced endothelium-dependent relaxation in small subcutaneous arteries in pregnancy.