Dopaminergic and opioidergic regulation of gonadotropin and prolactin release in stallions.
Abstract: In the non-breeding season, LH release is reduced via dopaminergic systems in the ram. On the other hand, our previous studies demonstrated an opioidergic inhibition of LH release in stallions outside the breeding season. Thus, in the present study we investigated the dopaminergic regulation of LH and prolactin secretion in stallions, considering interactions between dopamine and opioids. To achieve this, stallions (n=8) were treated with the dopamine antagonist sulpiride (0.6 mg/kg), the opioid antagonist naloxone (0.5 mg/kg), sulpiride plus naloxone or saline in December, March and June. Two hours after the respective treatments, they received a GnRH agonist. Sulpiride induced a significant prolactin release which was most pronounced in December, indicating seasonal variations in the inhibition of prolactin secretion by dopaminergic systems. Prolactin concentrations were not changed by naloxone. Neither during nor outside the breeding season, a dopaminergic regulation of LH release could be demonstrated. In contrast, naloxone caused a significant (p < 0.05) LH release, confirming an opioidergic inhibition of LH release. In conclusion, opioidergic regulation of LH and dopaminergic inhibition of prolactin secretion undergo seasonal changes. Neither during nor outside the breeding season, dopaminergic effects on LH release exist in the stallion.
Publication Date: 2002-12-05 PubMed ID: 12464071DOI: 10.1046/j.1439-0531.2002.00370.xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research study investigates how dopamine and opioids interact to regulate the secretion of certain hormones in stallions. The researchers found that opioids influence luteinizing hormone (LH) secretion, while dopamine affects prolactin secretion, and these effects vary seasonally.
Methods of the Study
- The researchers worked with 8 stallions as subjects, treating them with different substances: the dopamine antagonist sulpiride, the opioid antagonist naloxone, a combination of the two, or saline. This was carried out in three different months – December, March, and June – representing different seasonal periods.
- The goal of using such substances was to examine their impact on LH and prolactin secretion in stallions. Sulpiride blocks the effects of dopamine, allowing researchers to see what happens when dopamine’s influence is removed. Similarly, naloxone blocks the effects of opioids.
- Two hours after the respective treatments, the stallions received a Gonadotropin-releasing hormone (GnRH) agonist. GnRH is a hormone responsible for the release of LH and follicle-stimulating hormone (FSH) from the anterior pituitary gland.
Key Findings of the Study
- The study found that sulpiride, the dopamine blocker, induced significant prolactin release, with the strongest effect in December. This suggests a seasonal variation in how much dopamine inhibits prolactin secretion.
- Prolactin levels were not changed by naloxone, indicating that opioids do not have noticeable effects on prolactin secretion.
- Interestingly, no evidence was found to suggest dopaminergic regulation of LH release during or outside the breeding season. On the contrary, naloxone caused a significant LH release, demonstrating that opioids are involved in inhibiting LH release.
Conclusion of the Study
- The research concludes that opioidergic regulation of LH and dopaminergic inhibition of prolactin secretion undergo seasonal changes. These findings helped researchers understand how LH secretion in stallions is influenced by opioids, and not by dopamine, and how prolactin secretion in the same animals is regulated by dopamine and not opioids.
- In addition, these effects do not seem to be influenced by the breeding season, as no clear link between dopamine and LH release was found at any time of the year.
Cite This Article
APA
Aurich C, Gerlach T, Aurich JE, Hoppen HO, Lange J, Parvizi N.
(2002).
Dopaminergic and opioidergic regulation of gonadotropin and prolactin release in stallions.
Reprod Domest Anim, 37(6), 335-340.
https://doi.org/10.1046/j.1439-0531.2002.00370.x Publication
Researcher Affiliations
- Centre for Artificial Insemination and Embryo Transfer, University of Veterinary Sciences, Vienna, Austria. christine.aurich@vu-wien.ac.at
MeSH Terms
- Animals
- Area Under Curve
- Breeding
- Buserelin / pharmacology
- Dopamine Antagonists / pharmacology
- Horses / blood
- Horses / physiology
- Luteinizing Hormone / blood
- Luteinizing Hormone / metabolism
- Male
- Naloxone / pharmacology
- Narcotic Antagonists / pharmacology
- Prolactin / blood
- Prolactin / metabolism
- Seasons
- Secretory Rate / drug effects
- Sulpiride / pharmacology
Citations
This article has been cited 2 times.- Lehman MN, Ladha Z, Coolen LM, Hileman SM, Connors JM, Goodman RL. Neuronal plasticity and seasonal reproduction in sheep.. Eur J Neurosci 2010 Dec;32(12):2152-64.
- Semaan SJ, Murray EK, Poling MC, Dhamija S, Forger NG, Kauffman AS. BAX-dependent and BAX-independent regulation of Kiss1 neuron development in mice.. Endocrinology 2010 Dec;151(12):5807-17.
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