Effects of gonadal steroids on the opioid regulation of LH and prolactin release in ovariectomized pony mares.
Abstract: The aim of the present study was to investigate the role of ovarian steroids in the opioid regulation of LH and prolactin release in mares. Effects of the opioid antagonist naloxone on LH and prolactin secretion were determined in ovariectomized pony mares. The animals were pretreated with either progesterone (500 micrograms kg-1) or oestradiol benzoate (10 micrograms kg-1) for 8 days and subsequently with a combination of progesterone and oestradiol for an additional 8 days. Naloxone administration (0.5 mg kg-1 i.v.) resulted in a significant release of LH as well as prolactin in mares after pretreatment with either oestradiol benzoate or progesterone plus oestradiol benzoate (P < 0.05). No significant changes in LH and prolactin secretion were detected in progesterone-treated and non-steroid-treated ovariectomized mares. These results indicate that a prolonged oestrogen influence activates the opioid inhibition of LH and prolactin release in mares. In contrast to other species, progesterone alone does not activate a tonic opioid inhibition of LH and prolactin secretion, but modulates the effect of oestrogens. The opioid systems therefore seem to be regulated by a sequence of different steroid environments, as found during the oestrous cycle. The parallel increases in prolactin and LH secretion in mares may indicate a common regulatory pathway for these two hormones.
Publication Date: 1995-11-01 PubMed ID: 7490548DOI: 10.1677/joe.0.1470195Google Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research study explored how ovarian hormones influence the way opioids regulate the release of two other hormones, luteinizing hormone (LH) and prolactin, in female horses that have undergone ovary removal. The results suggest that extended exposure to the hormone estrogen triggers opioid systems to limit the release of LH and prolactin, while the hormone progesterone alone does not appear to activate this process, but adjusts the effect of estrogen.
Goal of the Research
- The research set out to explore the impact of ovarian hormones, particularly progesterone and oestradiol benzoate (a form of estrogen), on the opioid management of LH and prolactin hormones in mares, or adult female horses.
- The aim was to gain a more thorough understanding of the hormonal changes that occur over a mare’s estrous cycle, and the effects of these hormones on LH and prolactin release.
Methodology
- The study used naloxone, an opioid antagonist, to measure LH and prolactin secretion in ovariectomized (ovaries removed) pony mares.
- These mares were first pretreated with either progesterone or oestradiol benzoate for a period of 8 days. Following this, they received a combination of both hormones for another 8 days.
- The researchers then administered naloxone to the mares and studied the resultant impact on the release of LH and prolactin hormones.
Findings
- The study observed a significant release of LH and prolactin in mares pretreated with either oestradiol benzoate or a combination of progesterone and oestradiol benzoate.
- No notable changes were observed in LH and prolactin secretion in mares treated with only progesterone or those that received no steroid treatment.
Interpretation and Conclusion
- The study concluded that extended estrogen exposure activates opioid suppression of LH and prolactin release in mares.
- It was also observed that unlike other species, progesterone on its own does not activate a tonic opioid suppression of LH and prolactin, but it does alter the effect of estrogens.
- The researchers note that the opioid systems appear to be influenced by an array of different steroid environments, following the pattern noted during the estrous cycle.
- The simultaneous increases in prolactin and LH release could suggest that these two hormones share a common regulatory pathway.
Cite This Article
APA
Aurich C, Daels PF, Ball BA, Aurich JE.
(1995).
Effects of gonadal steroids on the opioid regulation of LH and prolactin release in ovariectomized pony mares.
J Endocrinol, 147(2), 195-202.
https://doi.org/10.1677/joe.0.1470195 Publication
Researcher Affiliations
- Institut für Reproduktionsmedizin, Tierärztliche Hochschule, Hannover, Germany.
MeSH Terms
- Animals
- Estradiol / blood
- Estradiol / pharmacology
- Female
- Gonadal Steroid Hormones / pharmacology
- Horses / blood
- Luteinizing Hormone / blood
- Luteinizing Hormone / metabolism
- Naloxone / pharmacology
- Narcotic Antagonists / pharmacology
- Ovariectomy
- Progesterone / blood
- Progesterone / pharmacology
- Prolactin / blood
- Prolactin / metabolism
- Radioimmunoassay
- Time Factors
Citations
This article has been cited 2 times.- Aurich C, Kaps M. Suppression of reproductive behaviour and gonadal function in female horses-An update. Reprod Domest Anim 2022 Sep;57 Suppl 4(Suppl 4):4-12.
- Okada CTC, Kaps M, Perez Quesada J, Gautier C, Aurich J, Aurich C. Diestrous Ovulations in Pregnant Mares as a Response to Low Early Postovulatory Progestogen Concentration. Animals (Basel) 2020 Nov 30;10(12).
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