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Serum and uterine fluid extracellular vesicles and prostaglandin E metabolite concentrations during diestrus and early pregnancy in mares.
Abstract: Prostaglandins produced by endometrial and conceptus tissues have an established role in maintaining luteal function in early pregnancy and initiating luteolysis during diestrus in mares. The cellular mechanisms controlling the secretion and delivery of prostaglandins have not been fully elucidated. We hypothesized that nanosized lipid bilayer extracellular vesicles (EV) that carry a variety of biological molecules would be involved in these key regulatory processes. Serum and uterine fluid samples were collected from diestrus and pregnant mares on day (D) 10 and D14 post-ovulation, and conceptuses were collected in pregnant mare cycles and cultured for 2-3 h. Extracellular vesicles were isolated using membrane affinity spin columns. Metabolomic EV cargo was assessed using LC-MS/MS, and cytosolic phospholipase A2 (cPLA2) with immunoblotting. Serum and uterine fluid PGEM and conceptus PGE concentrations were compared using ELISA. Prostaglandins were below detection limits in all EV serum and uterine fluid eluates. PGEM concentrations in uterine fluid and serum did not differ between pregnant and diestrus mares at these time points. Day 10 and D14 conceptuses produced PGE. Serum and uterine fluid EV contained AA and cPLA2. While AA abundance did not differ by reproductive status or day at these time points, uterine fluid EV AA abundance was 83 times higher than serum. Serum and uterine fluid EV carry activatable phospholipases and rate-limiting substrates for prostaglandin production rather than the prostaglandins themselves. High levels of AA in uterine fluid EV are likely important in the local regulation of uterine prostaglandin production.
© 2026. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2026-10-21 PubMed ID: 42905180PubMed Central: 4668677DOI: 10.1007/s00441-026-04101-5Google 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
Summary
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Serum and uterine fluid extracellular vesicles in mares carry important molecules necessary for prostaglandin production, but not prostaglandins themselves, suggesting a role in regulating uterine prostaglandin synthesis during early pregnancy and diestrus.
Background and Purpose
- Prostaglandins (PGs) are lipid compounds produced by the endometrium and conceptus tissue, essential for maintaining corpus luteum function in early pregnancy and triggering luteolysis during diestrus in mares.
- The exact cellular mechanisms responsible for the secretion and delivery of prostaglandins are not fully understood.
- The researchers hypothesized that extracellular vesicles (EVs), nanosized lipid bilayer particles carrying biological molecules, might play a key role in these regulatory mechanisms.
Study Design and Methods
- Samples were collected from mares during two reproductive states: diestrus and early pregnancy (on days 10 and 14 post-ovulation).
- Serum and uterine fluid samples were obtained, and conceptuses from pregnant mares were collected and cultured briefly (2-3 hours).
- Extracellular vesicles were isolated from the samples using membrane affinity spin columns, a method for capturing nanosized vesicles based on membrane properties.
- The content (cargo) of the EVs was analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify metabolites.
- The presence of cytosolic phospholipase A2 (cPLA2), an enzyme important in prostaglandin synthesis, was analyzed by immunoblotting.
- Prostaglandin E metabolite (PGEM) concentrations in serum and uterine fluid, and prostaglandin E (PGE) levels produced by cultured conceptuses, were measured by ELISA.
Key Results
- Prostaglandins themselves were below detectable levels in extracellular vesicles isolated from serum and uterine fluid, indicating EVs did not directly carry PGs.
- PGEM concentrations in serum and uterine fluid were not significantly different between pregnant and diestrus mares on days 10 and 14.
- Conceptuses collected on days 10 and 14 produced measurable amounts of PGE during culture.
- Extracellular vesicles in both serum and uterine fluid contained arachidonic acid (AA)—the rate-limiting substrate for prostaglandin synthesis—and the enzyme cPLA2 capable of releasing arachidonic acid from membrane phospholipids.
- The abundance of AA in uterine fluid EVs was approximately 83 times higher than in serum EVs, although AA levels did not vary significantly with reproductive status or day post-ovulation.
Conclusions and Implications
- Extracellular vesicles circulating in serum and present in uterine fluid carry crucial components needed to produce prostaglandins—such as arachidonic acid and activating enzymes—but not the prostaglandins themselves.
- The presence of high AA levels and cPLA2 within uterine fluid EVs suggests these vesicles supply key substrates and enzymes locally within the uterus to regulate prostaglandin production.
- This EV-mediated delivery system likely plays a significant role in the local control of uterine prostaglandin synthesis during critical periods of the reproductive cycle (diestrus and early pregnancy).
- Understanding this mechanism could provide insights into fertility regulation and the molecular processes that support pregnancy maintenance in mares.
Cite This Article
APA
Ghersa J, Mullan-Fraser M, Gesy K, Yousif N, Itogawa L, Manning S, MacPhee DJ, Card C.
(2026).
Serum and uterine fluid extracellular vesicles and prostaglandin E metabolite concentrations during diestrus and early pregnancy in mares.
Cell Tissue Res, 405(3), 17.
https://doi.org/10.1007/s00441-026-04101-5 Publication
Researcher Affiliations
- Dept. Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada. josefina.ghersa@usask.ca.
- Dept. Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
- Dept. Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
- Dept. Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
- Dept. Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
- Dept. Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
- Dept. Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
- Dept. Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
MeSH Terms
- Animals
- Female
- Pregnancy
- Horses
- Extracellular Vesicles / metabolism
- Diestrus / blood
- Diestrus / metabolism
- Uterus / metabolism
- Prostaglandins E / metabolism
- Prostaglandins E / blood
- Dinoprostone / metabolism
- Extracellular Fluid / metabolism
Conflict of Interest Statement
Declarations. Ethics approval: All procedures adhered to institutional and national standards for the care and use of animals and were approved by the University Committee on Animal Care and Supply (UCACS 2012004). Competing interests: The authors declare no competing interests.
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