Inhibin-A and Inhibin-B in stallions: Seasonal changes and changes after down-regulation of the hypothalamic-pituitary-gonadal axis.
Abstract: The biological function of inhibin is mediated by two heterodimers, inhibin-A and inhibin-B. The relative importance of inhibin-A and -B in male reproductive function varies considerably across species with inhibin-B predominating in many species, whereas inhibin-A appears relatively more important in rams. Research reported to date in stallions has examined total or immunoreactive (ir) inhibin which does not distinguish the two heterodimers. Therefore, the objective of this study was to characterize changes in inhibin-A and inhibin-B concentrations in stallions: 1) across season for a period of one year, and 2) after downregulation of the hypothalamic-pituitary-gonadal (HPG) axis. In Study one, serum samples were obtained monthly from five stallions for a period of one year. Serum concentrations of inhibin-A, inhibin-B, testosterone and estrone sulfate were determined by ELISA. In Study two, stallions were treated with the GnRH antagonist, acyline (n = 4; 330 mg/kg acyline IM) or vehicle control (n = 4; vehicle alone) every five days for 50 days. Plasma concentrations of inhibin-A and -B were determined by ELISA at Days 0, 6, 12, 22, 37, 59, 80, 87 and 104 after initiation of acyline treatment. Testis volume was determined by ultrasonography at weekly intervals. In Study 1, both inhibin-A and inhibin-B showed seasonal changes in concentration with highest concentrations in increasing day length and lowest concentrations in short day lengths. Inhibin-B (overall mean 107.8 ± 4.1 pg/mL) was present at 4.7-fold higher concentrations in serum than inhibin-A (overall mean 23.0 ± 0.7 pg/mL). In Study 2, plasma concentrations of inhibin-B but not inhibin-A were significantly downregulated by administration of the GnRH antagonist, acyline. When the HPG axis was downregulated by acyline, testis volume was strongly correlated with inhibin-B (r = 0.73; P < 0.05) but not inhibin-A (r = 0.22; P = 0.20). In summary, inhibin-B appears to be the predominant form of inhibin in the stallion which undergoes seasonal regulation along with other reproductive parameters and is co-regulated with other endocrine parameters of the HPG axis.
Copyright © 2019 Elsevier Inc. All rights reserved.
Publication Date: 2018-09-27 PubMed ID: 30296651DOI: 10.1016/j.theriogenology.2018.09.036Google Scholar: Lookup
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- Clinical Trial
- Veterinary
- Journal Article
Summary
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The research studies the changes in levels of two hormones, inhibin-A and inhibin-B, in stallions over different periods and under different conditions. It found that inhibin-B is more dominant in stallions, with its concentrations changing seasonally and in response to a specific treatment.
Objective and Importance of the Study
- The study aimed to investigate the variations in concentrations of two hormones, inhibin-A and inhibin-B, in stallions. These hormones are essential for regulating male reproductive function. While previous studies have looked into total or immunoreactive inhibin, this study distinguishes between the two forms, inhibin-A and inhibin-B.
- The goal of this work was to better understand how the levels of these hormones change across seasons and following the down-regulation of the hypothalamic-pituitary-gonadal (HPG) axis, an essential pathway for the endocrine regulation of reproductive organs.
Methodology and Results
- Two separate studies were conducted. In the first, monthly serum samples from five stallions were taken over a year, and the concentrations of inhibin-A and inhibin-B were measured, alongside testosterone and estrone sulfate.
- The results revealed that both inhibin-A and inhibin-B showed seasonal concentration changes, with the highest concentrations during increasing daylight lengths and the lowest during short daylight lengths. Further, inhibin-B was found at significantly higher concentrations than inhibin-A.
- In the second study, a group of stallions was treated with the GnRH antagonist, acyline, or a control treatment. The levels of inhibin-A and -B were measured at various points after the initiation of the treatment, alongside the determination of testis volume through ultrasonography.
- It was found that inhibin-B, but not inhibin-A, was significantly down-regulated by the acyline treatment. Additionally, when the HPG axis was down-regulated, inhibin-B displayed a strong correlation with testis volume, unlike inhibin-A.
Conclusion and Implications
- The study concludes that inhibin-B is the predominant form of inhibin in stallions and experiences seasonal regulation along with other reproductive parameters.
- The findings provide crucial insights into how the endocrine regulation of stallion reproduction works, particularly in relation to inhibin hormone forms. It can inform developments in treatments or strategies to control stallion fertility.
Cite This Article
APA
Ball BA, Davolli GM, Esteller-Vico A, Fleming BO, Wynn MAA, Conley AJ.
(2018).
Inhibin-A and Inhibin-B in stallions: Seasonal changes and changes after down-regulation of the hypothalamic-pituitary-gonadal axis.
Theriogenology, 123, 108-115.
https://doi.org/10.1016/j.theriogenology.2018.09.036 Publication
Researcher Affiliations
- Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, 40546, USA. Electronic address: b.a.ball@uky.edu.
- Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, 40546, USA.
- Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, 40546, USA.
- Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, 40546, USA.
- Maxwell H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, 40546, USA.
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA, 95616, USA.
MeSH Terms
- Animals
- Down-Regulation
- Estrone / analogs & derivatives
- Estrone / blood
- Horses / blood
- Horses / physiology
- Hypothalamo-Hypophyseal System / drug effects
- Hypothalamo-Hypophyseal System / physiology
- Inhibins / metabolism
- Male
- Oligopeptides / administration & dosage
- Oligopeptides / pharmacology
- Random Allocation
- Seasons
- Testis / drug effects
- Testis / physiology
- Testosterone / blood
Citations
This article has been cited 3 times.- Chen Y, Liu Q, Liu R, Yang C, Wang X, Ran Z, Zhou S, Li X, He C. A Prepubertal Mice Model to Study the Growth Pattern of Early Ovarian Follicles. Int J Mol Sci 2021 May 12;22(10).
- Akhtar MF, Swelum AA, Wang C. Effect of Monochromatic Red, Blue, and White Light on Reproductive Hormones of Male Donkeys During the Non-Breeding Season. Animals (Basel) 2026 Feb 4;16(3).
- Meng J, Feng J, Xiao L, Hu N, Lan X, Wang S. Oral vaccination with inhibin DNA vaccine for promoting spermatogenesis in rats. Anim Reprod 2024;21(4):e20230079.
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