Endocrine changes, fetal growth, and uterine artery hemodynamics after chronic estrogen suppression during the last trimester of equine pregnancy

Alejandro Esteller-Vico, Barry A. Ball, Mats H.T. Troedsson, Edward L. Squires

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Equine pregnancy is characterized by very high circulating concentrations of estrogens. The physiological roles of estrogens during equine gestation are largely unknown, although some studies suggest a role in the regulation of uterine artery hemodynamics and a relationship between low circulating estrogen concentrations and late pregnancy loss. The objectives of this experiment were to evaluate the effects of estrogen suppression on uterine artery hemodynamics and on pregnancy outcome. Estrogen synthesis was suppressed using letrozole, a potent aromatase inhibitor. Twelve pregnant mares were randomly assigned to a control (n = 6) or treatment (n = 6; 500 mg letrozole orally every 4 days) group with treatment starting at 240 days of gestation and continuing until parturition. Weekly serum samples were analyzed to determine testosterone, dehydroepiandrosterone sulfate, estradiol, estrone sulfate, progestins, and prostaglandin F2α metabolite concentrations. Ultrasonographic examinations were performed biweekly andmeasurements included uterine artery hemodynamics (diameter, pulsatility, and resistance indices), fetal growth using the diameter of the fetal eye, and placental evaluation using the combined thickness of the uterus and placenta. At parturition, gestational length, foal weight, and neonatal viability were determined. Letrozole suppressed estrogen synthesis during gestation by approximately 90% compared to control values. This large reduction in circulating estrogens had no effect on uterine artery hemodynamics, normal placental development, maintenance of pregnancy, or neonatal viability. However, neonates from letrozole-treated mares had lower (P < 0.05) birth weights than controls, suggesting that estrogens may play a role in fetal growth that is not mediated through regulation of uterine blood flow.

Original languageEnglish
Article numberbio140533
Pages (from-to)414-423
Number of pages10
JournalBiology of Reproduction
Issue number2
StatePublished - Feb 1 2017

Bibliographical note

Publisher Copyright:
© The Authors 2017. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved.


  • Aromatase
  • Equine
  • Estrogen
  • Letrozole
  • Pregnancy
  • Uterine blood flow

ASJC Scopus subject areas

  • Reproductive Medicine
  • Cell Biology


Dive into the research topics of 'Endocrine changes, fetal growth, and uterine artery hemodynamics after chronic estrogen suppression during the last trimester of equine pregnancy'. Together they form a unique fingerprint.

Cite this