Chronic hypoxia augments uterine artery distensibility and alters the circumferential wall stress-strain relationship during pregnancy

• Published in: Journal of applied physiology (1985) 2006-06, Vol.100 (6), p.1842-1850
• Main Authors: Mateev, Stephanie N, Mouser, Rhonda, Young, David A, Mecham, Robert P, Moore, Lorna G
• Format: Article
• Language: English
• Subjects: Animals; Arteries - anatomy & histology; Arteries - physiology; Biological and medical sciences; Biomechanical Phenomena; Blood Flow Velocity - physiology; Blood vessels; Body Weight - physiology; Chronic Disease; Circulatory system; Endothelium, Vascular - anatomy & histology; Endothelium, Vascular - physiology; Female; Fundamental and applied biological sciences. Psychology; Guinea Pigs; Hypoxia - physiopathology; Pre-Eclampsia - physiopathology; Pregnancy; Pregnancy, Animal - physiology; Regional Blood Flow - physiology; Uterus - blood supply; Uterus - physiology; Vasodilation - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00618.2005

1 Center for Women's Health Research and Cardiovascular Pulmonary Research Laboratory, 3 Department of Preventive Medicine and Biometrics, and 5 Department of Health and Behavioral Sciences, University of Colorado at Denver and Health Sciences Center, Denver, Colorado; 2 Department of Pediatrics, University of California, Davis Medical Center, Sacramento, California; and 4 Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri Submitted 24 May 2005 ; accepted in final form 12 January 2006 Pregnancy-associated increases in uterine artery (UA) blood flow are due, in part, to vasoactive and growth-related changes that enlarge UA diameter. Although active and passive mechanical factors can contribute to this enlargement, their role is less well understood. We hypothesized that pregnancy increased UA distensibility and/or decreased myogenic tone. Given the fetal growth restriction and lower UA flow seen under chronic hypoxia, we further hypothesized that chronic hypoxia opposed these normal active and passive mechanical changes. UA were isolated from 12 nonpregnant and 12 pregnant (0.7 gestation) guinea pigs housed under normoxia or chronic hypoxia (3,960 m) and studied by pressure myography. Pregnancy increased UA diameter similarly under normoxia and hypoxia. Although chronic hypoxia raised resting tone in UA from nonpregnant guinea pigs to 20% and tone was greater in preconstricted pregnant chronically hypoxic vs. normoxic UA (both P < 0.01), there was an absence of myogenic response (i.e., an increase in tone with rising pressure) in all groups. Pregnancy increased UA distensibility 1.5-fold but did not change stiffness or the stress-strain relationship. Compared with vessels from normoxic pregnant animals, hypoxic pregnancy raised UA distensibility fourfold, decreased stiffness (rate constant b = 3.80 ± 1.06 vs. 8.92 ± 1.25, respectively, P < 0.01), lowered elastin by 50%, and shifted the stress-strain relationship upward such that four times as much strain was present at a given stress. We concluded that increased distensibility and low myogenic tone contribute to enlarging UA diameter and raising UA blood flow during pregnancy. Chronic hypoxia exaggerates the rise in distensibility and alters the stress-strain relationship in ways that may provoke vascular injury. myogenic tone; preeclampsia; elastin; collagen; intrauterine growth restriction Address for reprint requests and other correspondence: S. N. Ma