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Role of prolactin in the gonadotroph responsiveness to gonadotrophin-releasing hormone during the equine annual reproductive cycle.
Abstract: A combined suppressive effect of prolactin (PRL) and dopamine on the secretion of luteinising hormone (LH) at the level of the pituitary gland has been identified in sheep, a short-day breeder. However, little is known about the role of PRL in the intra-pituitary regulation of the gonadotrophic axis in long-day breeders. In the present study, we investigated the effects of PRL on LH and follicle-stimulating hormone (FSH) secretion during the equine annual reproductive cycle. Horse pituitaries were obtained during the breeding season (BS) and nonbreeding season (NBS). Cells were dispersed, plated to monolayer cultures and assigned to one of the following specific treatments: (i) medium (Control); (ii) rat PRL (rPRL); (iii) thyrotrophin-releasing hormone (TRH); (iv) bromocriptine (Br); and (v) Br + rPRL. Gonadotrophin-releasing hormone (GnRH) dose-dependently stimulated LH release during the BS and NBS. During the BS, neither rPRL nor TRH affected the LH response to GnRH, but Br significantly (P < 0.01) enhanced both basal and GnRH-stimulated LH release through a mechanism that did not involve alterations in the concentrations of PRL. However, rPRL prevented the Br-induced increase in basal and GnRH-stimulated LH output, and suppressed LH below basal values (P < 0.05). Conversely, during the NBS, no significant effects of treatments were observed. Interestingly, at this time of year, the incidence of pituitary gap junctions within the pars distalis decreased by 50% (P < 0.01). By contrast to the effects on LH, no treatment effects were detected on the FSH response to GnRH, which was only apparent during the NBS. These results reveal no direct effects of PRL but an interaction between PRL and dopamine in the inhibitory regulation of LH, but not FSH, release at the level of the pituitary in the horse, and a modulatory role of season/photoperiod associated with alterations in folliculostellate cell-derived gap junctions.
Publication Date: 2010-03-02 PubMed ID: 20236228DOI: 10.1111/j.1365-2826.2010.01986.xGoogle 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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This study investigates how prolactin (PRL) impacts the release of luteinising hormone (LH) and follicle stimulating hormone (FSH) during a horse’s reproductive cycle. It found that the interaction between PRL and dopamine, not PRL alone, has an inhibitory effect on LH, but not FSH, release in horses during the breeding season.
Research Objectives
- This research sought to understand the role of prolactin (PRL) in the regulation of the gonadotrophic axis in long-day breeders, specifically horses, during their annual reproductive cycle.
- The effects of PRL on secretion of luteinising hormone (LH) and follicle-stimulating hormone (FSH) during horse’s breeding (BS) and nonbreeding season (NBS) were investigated.
Methodology
- Horse pituitaries were obtained during both the breeding and nonbreeding seasons.
- The cells were isolated and cultured under various treatments: medium (control); rat PRL (rPRL); thyrotrophin-releasing hormone (TRH); bromocriptine (Br), a drug that inhibits prolactin release; and a combination of Br and rPRL.
Findings
- Gonadotrophin-releasing hormone (GnRH) stimulated LH release during both the breeding and nonbreeding seasons in a dose-dependent manner.
- During the breeding season, neither rPRL nor TRH affected the LH response to GnRH. However, bromocriptine enhanced the release of LH, an effect that did not involve alterations in the concentrations of PRL. Intriguingly, rPRL prevented this bromocriptine-induced increase, thereby suppressing LH.
- No significant effects of these treatments were observed during the nonbreeding season.
- The incidence of pituitary gap junctions, which are channels that allow direct communication between cells, decreased by 50% during the NBS.
- None of the treatments affected the FSH response to GnRH, which was only apparent during the nonbreeding season.
Conclusion
- The study concluded that the inhibitory regulation of LH, but not FSH, release at the pituitary level in horses involves an interaction between PRL and dopamine, not PRL alone.
- This regulation varies with the breeding season and is associated with changes in folliculostellate cell-derived gap junctions, indicating the important role played by season and photoperiod in hormonal regulation within the equine reproductive cycle.
Cite This Article
APA
Hodson DJ, Townsend J, Gregory SJ, Walters C, Tortonese DJ.
(2010).
Role of prolactin in the gonadotroph responsiveness to gonadotrophin-releasing hormone during the equine annual reproductive cycle.
J Neuroendocrinol, 22(6), 509-517.
https://doi.org/10.1111/j.1365-2826.2010.01986.x Publication
Researcher Affiliations
- Department of Anatomy, University of Bristol, Bristol, England, UK.
MeSH Terms
- Animals
- Female
- Follicle Stimulating Hormone / metabolism
- Gap Junctions / metabolism
- Gonadotropin-Releasing Hormone / physiology
- Horses
- Immunohistochemistry
- Luteinizing Hormone / metabolism
- Prolactin / physiology
- Reproduction / physiology
- Seasons
Grant Funding
- Biotechnology and Biological Sciences Research Council
Citations
This article has been cited 4 times.- Le Tissier PR, Murray JF, Mollard P. A New Perspective on Regulation of Pituitary Plasticity: The Network of SOX2-Positive Cells May Coordinate Responses to Challenge. Endocrinology 2022 Aug 1;163(8).
- Castle-Miller J, Bates DO, Tortonese DJ. Mechanisms regulating angiogenesis underlie seasonal control of pituitary function. Proc Natl Acad Sci U S A 2017 Mar 21;114(12):E2514-E2523.
- Tortonese DJ. Intrapituitary mechanisms underlying the control of fertility: key players in seasonal breeding. Domest Anim Endocrinol 2016 Jul;56 Suppl(Suppl):S191-203.
- Taylor WA, Evans NP, Hertz C, Skinner DC. Intra-pituitary administration revisited: development of a novel in vivo approach to investigate the ovine hypophysis. J Neurosci Methods 2011 Aug 15;199(2):175-82.
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