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Seasonal variation in hypothalamic content of gonadotropin-releasing hormone (GnRH), pituitary receptors for GnRH, and pituitary content of luteinizing hormone and follicle-stimulating hormone in the mare.
Abstract: Seasonal changes in the hypothalamic-hypophyseal axis were investigated using tissue from 49 light-horse mares, of mixed breeding. Hypothalamic and pituitary tissues were collected at 5 intervals throughout the years 1981 and 1982, representing midbreeding season (July, n = 10), transition out of the breeding season (October, n = 11), midanestrus (December, n = 8), transition into the breeding season (March, n = 10), and again in the following midbreeding season (July, n = 10). The hypothalamic region was dissected into preoptic area, body and median eminence. Gonadotropin-releasing hormone (GnRH) was extracted from hypothalamic samples with methanol-formic acid and quantified by radioimmunoassay. The anterior pituitary was homogenized and receptors for GnRH were quantified in a crude membrane fraction. Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in the resulting supernatant. Content of GnRH in each of the 3 hypothalamic areas varied with season (P less than 0.01) and was lowest during midanestrus (P less than 0.05). There was no effect of season (P greater than 0.01) on either concentration or total number of receptors for GnRH, or concentration of FSH in the anterior pituitary. Concentrations of LH in the anterior pituitary varied with season (P less than 0.001). Means (+/- SEM) for the 5 collection times were 15.5 +/- 2.7, 9.7 +/- 2.4, 2.3 +/- 0.5, 2.7 +/- 0.4 and 11.7 +/- 1.5 microgram LH/mg anterior pituitary, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1984-06-01 PubMed ID: 6329338DOI: 10.1095/biolreprod30.5.1055Google 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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The research investigates how seasons affect certain hormones and receptors in the hypothalamus and pituitary gland of mares. It found that the content of gonadotropin-releasing hormone (GnRH) in the hypothalamus and the concentration of luteinizing hormone in the pituitary both change with the season.
Study Design and Sample Collection
- The study was conducted on 49 light-horse mares of mixed breeding.
- The researchers collected hypothalamic and pituitary tissues five times throughout two years, at different stages of the breeding season.
- The hypothalamic region was dissected into three parts: the preoptic area, body, and median eminence.
Methodology
- Gonadotropin-releasing hormone (GnRH) from the hypothalamic samples was extracted using methanol-formic acid and then quantified by radioimmunoassay.
- The anterior pituitary was homogenized, and receptors for GnRH were quantified in a crude membrane fraction.
- Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in the supernatant after homogenization.
Study Findings
- The research found that the GnRH content in all three areas of the hypothalamus changed with the season, and was the lowest during midanestrus (i.e., when the mares were not in heat).
- The study did not find any seasonal changes in the concentration or total number of GnRH receptors, or in the concentration of FSH in the anterior pituitary.
- The concentrations of LH in the anterior pituitary differed with the seasons, and the results of LH concentrations for the five collection times were also provided.
Conclusions
- This research sheds light on the fact that certain hormonal contents in the hypothalamus-hypophyseal axis of mares change according to the season. More specifically, it was observed that the content of GnRH in the hypothalamus and the concentration of LH in the pituitary show seasonal variations.
Cite This Article
APA
Hart PJ, Squires EL, Imel KJ, Nett TM.
(1984).
Seasonal variation in hypothalamic content of gonadotropin-releasing hormone (GnRH), pituitary receptors for GnRH, and pituitary content of luteinizing hormone and follicle-stimulating hormone in the mare.
Biol Reprod, 30(5), 1055-1062.
https://doi.org/10.1095/biolreprod30.5.1055 Publication
Researcher Affiliations
MeSH Terms
- Animals
- Estrus
- Female
- Follicle Stimulating Hormone / analysis
- Horses / physiology
- Hypothalamo-Hypophyseal System / analysis
- Hypothalamus / analysis
- Luteinizing Hormone / analysis
- Organ Size
- Ovary / anatomy & histology
- Pituitary Gland, Anterior / analysis
- Pituitary Hormone-Releasing Hormones / analysis
- Pregnancy
- Receptors, Cell Surface / analysis
- Receptors, LHRH
- Seasons
Citations
This article has been cited 8 times.- Wucher V, Sodaei R, Amador R, Irimia M, Guigó R. Day-night and seasonal variation of human gene expression across tissues. PLoS Biol 2023 Feb;21(2):e3001986.
- Kim S, Jung H, Murphy BA, Yoon M. Efficiency of Equilume light mask on the resumption of early estrous cyclicity and ovulation in Thoroughbred mares. J Anim Sci Technol 2022 Jan;64(1):1-9.
- Fanelli D, Tesi M, Rota A, Beltramo M, Conte G, Giorgi M, Barsotti G, Camillo F, Panzani D. hCG is more effective than the GnRH agonist buserelin for inducing the first ovulation of the breeding season in mares. Equine Vet J 2022 Mar;54(2):306-311.
- Wucher V, Sodaei R, Amador R, Irimia M, Guigó R. Day-night and seasonal variation of human gene expression across tissues. bioRxiv 2022 Jan 11;.
- Kwong GPS, Klein C. Deslorelin and naltrexone stimulate follicular development in mares during autumn transition and early anestrus. Can Vet J 2019 Aug;60(8):855-858.
- Alonso-Almorox P, Blanco A, Fiorito C, Gómez-Villamandos JC, Risalde MA, Almunia J, Fernández A. The orca (Orcinus orca) pituitary gland: an anatomical, immunohistochemical and ultrastructural analysis. Front Neuroanat 2025;19:1626079.
- Alonso-Almorox P, Blanco A, Fiorito C, Sierra E, Suárez-Santana C, Consolli F, Arbelo M, Guzmán RG, Molpeceres-Diego I, Fernández Gómez A, Almunia J, Castro-Alonso A, Fernández A. Dolphin Pituitary Gland: Immunohistochemistry and Ultrastructural Cell Characterization Following a Novel Anatomical Dissection Protocol and Non-Invasive Imaging (MRI). Animals (Basel) 2025 Mar 4;15(5).
- Harmat L, Nagy J, Somoskői B, Alpár A, Fekete SG, Gáspárdy A. Determination of Rhythmicity and Gestational Stage-Related Distribution of Blood Plasma Melatonin Concentrations in Donkey Mares. Vet Sci 2024 Jul 11;11(7).
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