Placental progestagens in the sheep and horse and the changes leading to parturition.
Abstract: Placental progestagen production and metabolism during pregnancy, the changes which precede parturition and the extent of fetal involvement in the latter processes are compared in the sheep and the horse. Neither species requires the presence of a corpus luteum for maintenance of the latter part of pregnancy, but the mechanisms involved in placental progesterone/progestagen production are very different in the two species. In sheep the primary product is progesterone (P4), levels of which are high in the maternal but not the fetal circulations. By contrast, in the mare P4 is not detectable in maternal blood after 200 days gestation although it is present in the placenta and fetal circulation. A range of P4 metabolites (primarily 5 alpha-pregnanes) are produced by the equine placenta, while in the fetus pregnenolone and its metabolites are the predominant progestagens. In sheep the prepartum endocrine cascade in which the rise in fetal cortisol stimulates enzyme changes in the placenta so that P4 declines and estrogens and prostaglandins eventually rise, is fairly well established compared with the events preceding delivery in the mare. In the latter species there is a gradual rise in progestagens for 10-20 days before term, at a time when the fetal adrenal is relatively quiescent and unresponsive to ACTH i.e. fetal cortisol levels are low. In the last 24-48 h before delivery maternal progestagens fall, just after fetal plasma cortisol concentrations begin to escalate. The ways in which maternal and fetal prepartum endocrine changes may be interrelated and the possibility of a fetal trigger to parturition in the mare are discussed.
Publication Date: 1994-01-01 PubMed ID: 7995342DOI: 10.1055/s-0029-1211284Google Scholar: Lookup
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Summary
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The research article focuses on the production and metabolism of placental progestagens (hormones) in sheep and horses during pregnancy and the changes leading to birth, highlighting the significant differences between the two species.
Placental Progestagens and Pregnancy
- The study explores the process of progestagen production and metabolism during pregnancy and the changes that occur before parturition (childbirth) in both sheep and horses.
- The research identifies that neither the sheep nor the horse require a corpus luteum, a temporary endocrine organ involved in ovulation and early pregnancy, for the maintenance of the latter part of the pregnancy.
- The mechanisms by which the placentas of sheep and horses produce progestagens, a group of hormones including progesterone, differ considerably. Progesterone is the primary hormone produced in sheep with high levels in the maternal but not the fetal circulation. On the other hand, in mares, progesterone is not detectable in the maternal blood after 200 days of gestation, although it can be found in the placenta and fetal circulation.
Metabolites and Pre-Partum Endocrine Cascade
- Different types of progesterone metabolites, primarily 5 alpha-pregnanes, are produced by the equine placenta. In the fetus, pregnenolone and its metabolites are the primary progestagens.
- In sheep, there’s a well-established pre-partum endocrine cascade, a series of hormonal changes. This cascade starts with the rise of fetal cortisol, stimulating changes in the placenta that cause a decline in progesterone and a subsequent rise in estrogens and prostaglandins, signaling impending birth.
Events Preceding Delivery
- Events before delivery in mares present a contrasting picture. Progestagens increase gradually for about 10 to 20 days before term, even when the fetal adrenal gland isn’t producing much cortisol and isn’t responsive to the hormone ACTH.
- In the final 24 to 48 hours before delivery, maternal progestagens drop, just as fetal plasma cortisol begins to increase sharply.
Interrelation of Prepartum Endocrine Changes and Fetal Trigger
- The article discusses how the hormonal changes in the mother and fetus before birth might be interconnected.
- It raises the possibility of a ‘fetal trigger’ to childbirth in mares, suggesting that the fetus might initiate the onset of labour.
Cite This Article
APA
Silver M.
(1994).
Placental progestagens in the sheep and horse and the changes leading to parturition.
Exp Clin Endocrinol, 102(3), 203-211.
https://doi.org/10.1055/s-0029-1211284 Publication
Researcher Affiliations
MeSH Terms
- Animals
- Female
- Gestational Age
- Horses / metabolism
- Labor Onset / metabolism
- Placenta / metabolism
- Pregnancy
- Progesterone / metabolism
- Progestins / biosynthesis
- Progestins / metabolism
- Sheep / metabolism
Citations
This article has been cited 5 times.- Ashraf R, Rashid S, Rasheed I, Asif S. Early embryonic death in equines and camelids. Open Vet J 2022 Nov-Dec;12(6):903-909.
- Canciello A, Teti G, Mazzotti E, Falconi M, Russo V, Giordano A, Barboni B. Progesterone Prolongs Viability and Anti-inflammatory Functions of Explanted Preterm Ovine Amniotic Membrane. Front Bioeng Biotechnol 2020;8:135.
- Mauro A, Sanyal H, Canciello A, Berardinelli P, Russo V, Bernabò N, Valbonetti L, Barboni B. In Vitro Effect of Estradiol and Progesterone on Ovine Amniotic Epithelial Cells. Stem Cells Int 2019;2019:8034578.
- Canciello A, Russo V, Berardinelli P, Bernabò N, Muttini A, Mattioli M, Barboni B. Progesterone prevents epithelial-mesenchymal transition of ovine amniotic epithelial cells and enhances their immunomodulatory properties. Sci Rep 2017 Jun 19;7(1):3761.
- Hümmelchen H, Wagner H, Brügemann K, König S, Wehrend A. Effects of Breeding for Short-Tailedness in Sheep on Parameters of Reproduction and Lamb Development. Vet Med Sci 2025 Jan;11(1):e70138.
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