Ontogeny of uteroplacental progestagen production in pregnant mares during the second half of gestation.
Abstract: In pregnant mares during late gestation, little, if any, progesterone (P4) is found in the maternal circulation. Hence, quiescence of the equine uterus is believed to be maintained by metabolites of pregnenolone and P4 known as progestagens, which are produced by the uteroplacental tissues. However, little is known about the ontogeny, distribution, or actual rates of uteroplacental progestagen production in pregnant mares and their fetuses during the second half of pregnancy. Therefore, the present study measured the rates of uteroplacental uptake and output of eight specific progestagens in chronically catheterized, pregnant pony mares from 180 days to term. No significant uteroplacental uptake of any of the eight individual progestagens was observed from the uterine circulation. In contrast, significant uteroplacental uptake was observed for five of the eight individual progestagens from the umbilical circulation, and the uptakes increased toward term. The major uteroplacental progestagen outputs were 5 alpha-pregnane-3,20-dione (5 alphaDHP) and 20 alpha-hydroxy-5 alpha-pregnan-3-one (20 alpha 5P). These were released into both the umbilical and uterine circulations at rates that increased toward term. The majority of the total uteroplacental 20 alpha 5P output was distributed into the uterine circulation at all gestational ages studied. In contrast, distribution of the total uteroplacental 5 alphaDHP output switched from preferential delivery into the uterine circulation before 220 days of gestation to release predominantly into the umbilical circulation after 260 days. These findings demonstrate that uteroplacental progestagen production changes during the second half of gestation, which may have important implications for the maintenance of pregnancy and the onset of labor in the mare.
Publication Date: 2003-04-16 PubMed ID: 12700198DOI: 10.1095/biolreprod.102.013292Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research investigates how the production of certain hormonal substances, called progestagens, by the uterine and placental tissues in pregnant horses, changes during the latter half of pregnancy. The study indicates that these changes may be important for successful pregnancy maintenance and timely commencement of labor.
Objective of the Research
- The purpose of this study is to evaluate the variations in the uteroplacental production of progestagens during the second half of gestation in pregnant mares. Progestagens are metabolites of progesterone, a hormone that plays a crucial role in maintaining pregnancy. The researchers aim to determine the amount, distribution, and rates of various specific progestagens produced in and around the uteroplacental unit. Understanding this could provide insights into mechanisms of how pregnancy is maintained and how labor is initiated in mares.
Methods Employed
- Eight specific progestagens were examined in this study, which was conducted on mares from the day 180 of pregnancy until term. The included mares were chronically catheterized, a procedure that allowed the researchers to monitor the progestagens level directly from the umbilical and uterine circulations.
Key Findings
- The researchers revealed no significant uptake of any of the eight progestagens from the uterine circulation. However, five of the examined progestagens demonstrated significant uptake from the umbilical circulation, with uptake levels rising as term approached.
- Two progestagens, 5 alpha-pregnane-3,20-dione (5 alphaDHP) and 20 alpha-hydroxy-5 alpha-pregnan-3-one (20 alpha 5P), were the primary outputs into both the umbilical and uterine circulations. Production of these two hormones increased as the term approached.
- The majority of the 20 alpha 5P was distributed into the uterine circulation, while 5 alphaDHP delivery switched from the uterus to the umbilical circulation after approximately 260 days of gestation.
Implications of the Findings
- The vertiginous rate of production and distribution of progestagens during the latter half of gestation could hold implications for how pregnancy is maintained and when labor is initiated in mares. The obtained results illustrate the essential role that progestagens play in the mare’s pregnancies, necessitating further studies to understand their deeper involvement in the birthing process.
Cite This Article
APA
Ousey JC, Forhead AJ, Rossdale PD, Grainger L, Houghton E, Fowden AL.
(2003).
Ontogeny of uteroplacental progestagen production in pregnant mares during the second half of gestation.
Biol Reprod, 69(2), 540-548.
https://doi.org/10.1095/biolreprod.102.013292 Publication
Researcher Affiliations
- Department of Physiology, University of Cambridge, Cambridge, CB2 3EG, United Kingdom.
MeSH Terms
- Animals
- Blood Gas Analysis
- Female
- Fetus / metabolism
- Gas Chromatography-Mass Spectrometry
- Horses / physiology
- Placenta / metabolism
- Pregnancy
- Pregnancy, Animal / physiology
- Progestins / biosynthesis
- Progestins / blood
- Uterus / metabolism
Citations
This article has been cited 4 times.- Boakari YL, Legacki E, Alonso MA, Dos Santos ACF, Nichi M, Conley AJ, Fernandes CB. Postnatal Dynamics of Circulating Steroid Hormones in Mule and Equine Neonates. Vet Sci 2022 Oct 28;9(11).
- Swink JM, Rings LM, Snyder HA, McAuley RC, Burns TA, Dembek KA, Gilsenan WF, Browne N, Toribio RE. Dynamics of androgens in healthy and hospitalized newborn foals. J Vet Intern Med 2021 Jan;35(1):538-549.
- Scholtz EL, Krishnan S, Ball BA, Corbin CJ, Moeller BC, Stanley SD, McDowell KJ, Hughes AL, McDonnell DP, Conley AJ. Pregnancy without progesterone in horses defines a second endogenous biopotent progesterone receptor agonist, 5α-dihydroprogesterone. Proc Natl Acad Sci U S A 2014 Mar 4;111(9):3365-70.
- Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K. Effect of birth month on endocrine function in Thoroughbred foals born in Hokkaido, the northern part of Japan. J Vet Med Sci 2025 Jul 7;87(7):804-815.
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