Involvement of endogenous opioids in the regulation of LH and testosterone release in the male horse.
Abstract: To investigate the involvement of endogenous opioids in the regulation of gonadotrophin release in male horses, effects of the opioid antagonist naloxone (0.5 mg kg-1 i.v.) on plasma LH and testosterone concentrations and the possible influence of season and of gonadal steroids were investigated. To determine quantitative as well as qualitative changes in gonadotrophin release, LH concentrations were measured by radioimmunoassay and by an in vitro bioassay. Experiments were performed in May, August and December. In stallions, basal LH secretion in May and August was significantly higher than in December (May versus December: P < 0.01; August versus December: P < 0.05); plasma testosterone concentrations were highest in August (August versus May: P < 0.05, August versus December: P < 0.001). The basal bioactive LH concentration and the ratio of bioactive:immunoreactive LH in stallions were highest in May. Therefore, in addition to seasonal changes in quantitative LH secretion, the bioactivity of LH in the circulation also undergoes seasonal variations. Bioactive LH concentrations and the bioactive:immunoreactive ratio in geldings were higher than in stallions. Naloxone caused a significant increase in LH release in stallions in August and December (P < 0.001); no significant increase was found in May (P = 0.06). In geldings, naloxone did not induce any changes in LH secretion; in stallions, a highly significant correlation was observed between basal testosterone concentrations and the LH increment after injection of naloxone (P < 0.001). In August and December, the bioactive:immunoreactive ratio increased significantly (P < 0.05) after injection of naloxone in stallions, indicating a preferential release of LH molecules with high bioactivity. The bioactive:immunoreactive ratio did not change after naloxone injection in May. The naloxone-induced LH release was followed by a significant increase in plasma testosterone concentrations in stallions in August (P < 0.001) and December (P < 0.05). In conclusion, endogenous opioid systems are involved in the regulation of LH and testosterone secretion in stallions. These mechanisms undergo seasonal changes: their activity is increased during winter and decreased during the breeding season. By affecting LH release, endogenous opioids, at least in part, regulate seasonal changes in reproductive activity in the stallion.
Publication Date: 1994-11-01 PubMed ID: 7861385DOI: 10.1530/jrf.0.1020327Google 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
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.
The research paper explores the role of endogenous opioids in the regulation of two hormones — luteinizing hormone (LH) and testosterone — in male horses, including seasonal variations and the impact of naloxone, an opioid antagonist.
Research Objective and Approach
- The purpose of this study was to unravel the involvement of endogenous opioids (naturally occurring substances similar to opiates) in controlling the release of gonadotropin hormones (such as LH) in male horses.
- The study assessed the effects of naloxone, a substance known to counteract the effects of opioids, on levels of LH and testosterone hormones. Moreover, the potential influence of seasons and other gonadal steroids on these hormones was also examined.
- The research employed radioimmunoassay and in vitro bioassay techniques to determine both the quantitative (amount) and qualitative (functional) changes in LH release.
Findings
- The study found that basal (standard, non-stimulated) LH secretion was significantly higher in May and August when compared with December. Similarly, testosterone was highest in August.
- Interestingly, not just the quantity, but the bioactivity (functional effectiveness) of LH circulating in the body also exhibited seasonal variations with the highest concentrations observed in May.
- Furthermore, it was observed that bioactive LH concentrations in geldings (castrated horses) were higher than in stallions (intact males).
- Naloxone, the opioid antagonist, resulted in a substantial increase in LH release in August and December, indicating a role of opioid systems in LH regulation.
- A strong correlation was found between baseline testosterone levels and the increase in LH following naloxone injection, implying a link between endogenous opioid regulation and testosterone secretion.
Conclusions
- The endogenous opioid system appears to play a significant role in controlling LH and testosterone secretion in male horses. These opioid mechanisms exhibit seasonal changes, with increased activity during winter and decreased activity during the breeding season.
- By affecting the release of LH, endogenous opioids regulate seasonal changes in reproductive activity in stallions. This fundamental understanding could have implications for managing horse breeding and fertility research.
Cite This Article
APA
Aurich C, Sieme H, Hoppe H, Schlote S.
(1994).
Involvement of endogenous opioids in the regulation of LH and testosterone release in the male horse.
J Reprod Fertil, 102(2), 327-336.
https://doi.org/10.1530/jrf.0.1020327 Publication
Researcher Affiliations
- Institut für Reproduktionsmedizin, Tierärztliche Hochschule, Hannover, Germany.
MeSH Terms
- Animals
- Biological Assay
- Horses / physiology
- Luteinizing Hormone / blood
- Luteinizing Hormone / metabolism
- Male
- Opioid Peptides / physiology
- Radioimmunoassay
- Seasons
- Secretory Rate / drug effects
- Testosterone / blood
- Testosterone / metabolism
Citations
This article has been cited 1 times.- Sheldon SA, Aleman M, Costa LRR, Santoyo AC, Weich KM, Howey Q, Madigan JE. Luteinizing hormone concentrations in healthy horses and horses with trigeminal-mediated headshaking over an 8-hour period. J Vet Intern Med 2019 Mar;33(2):885-888.
Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
