Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion.
Abstract: Concentrations of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion. Further, gonadotrophin concentrations in geldings are reported to return to values within the normal range of the entire stallion. In an attempt to characterize this species-specific reversal, the gonadotrophin concentrations of 6 male ponies castrated on 25 March were monitored for 4 months, and 4 stallions were used to generate control data. Blood samples were collected daily, from 3 d before to 10 d after castration (Day 0), and weekly thereafter until Day 122. The pituitary response to castration was immediate. Castration resulted in a previously unreported, dramatic (13-fold) but transient (3 d) surge in circulating concentrations of LH. Concentrations of LH and FSH increased in a logarithmically scaled (LH, R2 = 0.77; FSH, R2 = 0.93) manner over the subsequent 5 wk, during which temporal changes in concentrations of both hormones were strongly correlated (R2 = 0.97). The ratio of plasma gonadotrophin concentrations was consistent throughout (LH:FSH, 1.43 +/- 0.04). Maximal concentrations of LH (20.58 +/- 1.97 ng/mL, Day 34.8 +/- 3.2) were attained approximately 2 wk before the peak in FSH (16.99 +/- 1.97 ng/mL, Day 49.7 +/- 3.0). Plasma gonadotrophin concentrations exceeded those of entire stallions throughout the study. The equine testes inhibited LH secretion during the early breeding season, and no chronic decrease in plasma gonadotrophin concentrations was recorded. However, the LH surge evident for 3 d immediately afer castration, may be related to the dynamic seasonal interaction between gonadal steroids and the regulation of pituitary gonadotrophin release.
Publication Date: 2001-04-27 PubMed ID: 11322243DOI: 10.1016/s0093-691x(01)00475-7Google Scholar: Lookup
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- Journal Article
Summary
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The research investigates hormonal changes specifically in gonadotrophin and prolactin levels, in pony stallions after castration during the early breeding season. The study aims to uncover the role of gonads in hormonal regulation and post-castration hormonal levels equilibrium in geldings, the neutered male horses.
Methodology
- The study was conducted on six pony stallions which were castrated on the same day, 25th of March, with four intact stallions used as controls.
- Blood samples from these subjects were taken every day, starting from 3 days prior to the castration till 10 days after. Weekly samples were collected thereafter up to the 122nd day.
- The researchers noted levels of two hormones – gonadotrophins (Luteinizing Hormone or LH and Follicle Stimulating Hormone or FSH) and prolactin.
Findings
- The drop in testosterone levels, due to castration, was immediately responded by the pituitary gland, which is responsible for the production of gonadotrophins.
- There was an unexpected and extremely swift (13-fold) increase in circulating LH levels, but it only lasted for three days.
- Thereafter, concentrations of both LH and FSH hormones followed an increasing logarithmic pattern over the next five weeks. The parallel increase in both the hormones suggested a strong correlation between changes in their levels.
- The LH:FSH ratio remained consistent throughout the investigation.
- The maximum concentration of LH was reached near the 35th day, about two weeks earlier than FSH, which peaked near day 50.
- It was observed that the gonadotrophin levels exceeded that of intact stallions at all times during the study.
Conclusion
- The study indicates that the equine testes suppress LH secretion during the early breeding season, and no long-term decrease in plasma gonadotrophin concentrations was recorded post-castration.
- The sudden but brief surge in LH immediately after castration suggests there may be a complex seasonal interaction between gonadal steroids and the regulation of pituitary gonadotrophin release.
Cite This Article
APA
Collingsworth MG, Fuller Z, Cox JE, Argo CM.
(2001).
Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion.
Theriogenology, 55(5), 1171-1180.
https://doi.org/10.1016/s0093-691x(01)00475-7 Publication
Researcher Affiliations
- School of Biological and Earth Science, Liverpool John Moores University, UK.
MeSH Terms
- Animals
- Follicle Stimulating Hormone / blood
- Horses / blood
- Luteinizing Hormone / blood
- Male
- Orchiectomy
- Prolactin / blood
- Regression Analysis
- Time Factors
Citations
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