Influences of season and artificial photoperiod on stallions: pituitary and testicular responses to exogenous GnRH.
Abstract: Effects of season and photoperiod on the anterior pituitary gland and testes were studied by responses to exogenous GnRH. Stallions were assigned to one of three treatments: 1) control, exposed to natural day length; 2) S-L, 8 h of light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984; or 3) S-S, 8:16 from July 16, 1982 until March 5, 1984. Approximately every 8 wk, stallions were administered GnRH (2 micrograms/kg BW) and blood was sampled at 20-min intervals for 2 h before and 8 h after GnRH administration. Concentrations of LH, FSH and testosterone were determined. Baseline concentrations (mean of pre-GnRH samples) of all hormones fluctuated seasonally (P less than .05), but only LH and testosterone displayed seasonal changes (P less than .05) in maximum response to GnRH (highest concentration above baseline after GnRH). The FSH response to GnRH was not affected (P greater than .05) by season, photoperiod or the season X treatment interaction. Exposure of S-L stallions to 16:8 in December resulted in early recrudescence of baseline concentrations of LH, FSH and testosterone. Maximum concentration of testosterone in response to GnRH was stimulated by 16:8, but the increase in baseline LH concentrations in S-L stallions was not associated with an increase in maximum LH response to GnRH. Seasonal patterns of baseline concentrations of FSH and testosterone and maximum LH response to GnRH in S-S stallions were similar to those for control stallions.(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1989-03-01 PubMed ID: 2498279DOI: 10.2527/jas1989.673763xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study investigates the effects of seasonal changes and artificial lighting on the pituitary gland and testes of stallions through response to administered Gonadotropin-releasing hormone (GnRH). It found these factors impact the levels of Luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone in the stallions’ systems.
Objective of Study
- This research was carried out to determine how season and photoperiod, that is, the length of an organism’s daily exposure to light, influence the responses of the pituitary gland and testes in horses to exogenous (externally administered) Gonadotropin-releasing hormone (GnRH).
Methodology
- Stallions were divided into three groups – a control group exposed to natural day length, a second group exposed to 8 hours of light and 16 hours of dark for 20 weeks (S-L group), and a third group exposed to the same 8:16 ratio from July 1982 until March 1984 (S-S group).
- Every 8 weeks, GnRH was administered to the stallions and then blood samples were taken at regular intervals before and after the administration.
- These samples were then examined for concentrations of LH, FSH, and testosterone.
Findings
- All hormones displayed seasonal fluctuations, with only Luteinizing hormone (LH) and testosterone showing seasonal differences in their maximum response to GnRH.
- The Follicle-stimulating hormone (FSH) response to GnRH appeared to be unaffected by season or light exposure.
- The S-L group displayed early signs of increased baseline concentrations of LH, FSH and testosterone after exposure to 16 hours of light in the winter.
- This increased light exposure stimulated a maximum concentration of testosterone response to GnRH but did not increase the maximum LH response.
- The S-S group showed similar patterns to the control group for baseline concentrations of FSH and testosterone, and maximum LH responses to GnRH.
Significance
- This study provides insights into the hormonal interplay and its relation to seasonal changes and light exposure in stallions. Such findings can contribute to various fields, including equine health management and breeding practices.
Cite This Article
APA
Clay CM, Squires EL, Amann RP, Nett TM.
(1989).
Influences of season and artificial photoperiod on stallions: pituitary and testicular responses to exogenous GnRH.
J Anim Sci, 67(3), 763-770.
https://doi.org/10.2527/jas1989.673763x Publication
Researcher Affiliations
- Anim. Reprod. Lab., Colorado State Univ., Fort Collins 80523.
MeSH Terms
- Animals
- Follicle Stimulating Hormone / blood
- Follicle Stimulating Hormone / metabolism
- Gonadotropin-Releasing Hormone / pharmacology
- Horses / physiology
- Light
- Luteinizing Hormone / blood
- Luteinizing Hormone / metabolism
- Male
- Periodicity
- Pituitary Gland, Anterior / drug effects
- Pituitary Gland, Anterior / metabolism
- Seasons
- Testis / drug effects
- Testis / metabolism
- Testosterone / blood
- Testosterone / metabolism
Citations
This article has been cited 1 times.- Akhtar MF, Swelum AA, Wang C. Effect of Monochromatic Red, Blue, and White Light on Reproductive Hormones of Male Donkeys During the Non-Breeding Season. Animals (Basel) 2026 Feb 4;16(3).
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