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Endocrine reviews1991; 12(1); 27-44; doi: 10.1210/edrv-12-1-27

Equine chorionic gonadotropin.

Abstract: Cells from the chorionic girdle of the equine trophoblast invade the maternal endometrium at day 36 of gestation and become established as secretory elements known as the endometrial cups. These structures, which persist for 40-60 days, produce a gonadotropin which can be found in circulation until about day 130 of gestation. This glycoprotein has been identified in the horse and the donkey, with the former having received much better characterization. It consists of 2 noncovalently linked peptide chains; an alpha-subunit of 96 amino acids, which is common to that found in other horse glycoprotein hormones. The beta-subunit of 149 amino acids is identical to horse LH beta. Horse CG is the most heavily glycosylated of the known pituitary and placental glycoprotein hormones. The alpha-subunit has two and the beta-subunit one N-linked glycosylation site, and the beta-chain has in excess of four O-linked glycosylation sites. The N-linked glycans have some oligosaccharides that are not found on other glycoprotein hormones. The sialic component of glycosylation confers an exceptionally long half-life on CG compared to other glycoprotein hormones. Horse CG has LH-like activity in horse receptor and in vitro bioassays. In spite of the amino acid homology, it has lower LH activity than does horse LH. Its most intriguing, and as yet unexplained, characteristic is its pronounced FSH and LH activity in species other than the horse. Horse CG binds to FSH receptors of virtually all mammalian species, other than the horse, in which it has been tested and will produce biological effects peculiar to FSH. It has similar and potent interaction with LH receptors. The structural basis of this duality is not known but may be related to the region 90-110 of the beta-chain. Horse CG is believed to be constitutively expressed by the trophoblastic cells until the endometrial cups degenerate. The role of CG in equine gestation is not completely understood. It is believed to act as an LH-like hormone to induce supplementary ovulation and/or luteinization of follicles in the mare. It has not been established whether CG or the accessory corpora lutea are necessary for successful horse pregnancy. They may serve as a redundant system to assure that there is sufficient secretion of the primary corpus luteum to maintain pregnancy until the placenta assumes its role as the principal steroidogenic organ of gestation.
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Publication Date: 1991-02-01 PubMed ID: 2026120DOI: 10.1210/edrv-12-1-27Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research paper is about the formation and functions of equine chorionic gonadotropin (CG), a significant hormone that is produced during an equine pregnancy. It primarily discusses the unique properties of this hormone, its production by endometrial cups, and its critical, although not fully understood, role in equine gestation.

Formation of Equine Chorionic Gonadotropin

  • The formation of equine Chorionic Gonadotropin (CG) occurs around the 36th day of gestation in horses and donkeys, when cells from the chorionic girdle of the equine trophoblast invade the maternal endometrium.
  • These cells establish as endometrial cups, which are secretory structures that produce the gonadotropin which can be detected in circulation until approximately the 130th day of gestation.
  • Equine CG consists of two non-covalently linked peptide chains, including an alpha-subunit of 96 amino acids common to horse glycoprotein hormones and a beta-subunit of 149 amino acids, identical to horse LH beta.

Characteristics of Equine CG

  • Equine CG is the most heavily glycosylated among the known pituitary and placental glycoprotein hormones, with numerous N-linked and O-linked glycosylation sites.
  • The sialic indigents present in glycosylation grant CG an exceptionally long half-life, in comparison to other glycoprotein hormones.
  • Despite its amino acid homology with horse Luteinizing Hormone (LH), equine CG possesses less LH activity than the horse LH itself. However, it exhibits a remarkable FSH and LH activity in species other than the horse.
  • Equine CG interacts effectively with Follicle Stimulating Hormone (FSH) receptors of nearly all mammalian species, excluding the horse, leading to biological effects specific to FSH.

Role of Equine CG in Equine Gestation

  • Although the specific function of equine CG in horse gestation is not fully grasped, it is understood that it behaves as an LH-like hormone, causing supplementary ovulation or luteinization of follicles in the mare.
  • It is yet to be determined whether CG or accessory corpora lutea are prerequisites for a successful horse pregnancy. They might serve as an auxiliary system that ensures sufficient secretion of the primary corpus luteum to preserve pregnancy, until the placenta takes over as the main steroidogenic organ of gestation.

Cite This Article

APA
Murphy BD, Martinuk SD. (1991). Equine chorionic gonadotropin. Endocr Rev, 12(1), 27-44. https://doi.org/10.1210/edrv-12-1-27

Publication

Endocrine reviews
ISSN: 0163-769X
NlmUniqueID: 8006258
Country: United States
Language: English
Volume: 12
Issue: 1
Pages: 27-44

Researcher Affiliations

Murphy, B D
  • Department of Obstetrics and Gynecology, University of Saskatchewan, Saskatoon, Canada.
Martinuk, S D

    MeSH Terms

    • Amino Acid Sequence
    • Amino Acids / analysis
    • Animals
    • Gonadotropins, Equine / analysis
    • Gonadotropins, Equine / chemistry
    • Gonadotropins, Equine / metabolism
    • Horses
    • Molecular Sequence Data

    References

    This article includes 164 references

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