Growth hormone and prolactin concentrations in plasma of horses: sex differences and the effects of acute exercise and administration of growth hormone-releasing hormone.
Abstract: Three experiments were conducted to determine 1) the relationship between prolactin and growth hormone (GH) secretion in mares and the response to GH-releasing hormone (GHRH), 2) whether plasma GH and prolactin concentrations differed among mares, stallions, and geldings, and 3) whether sexual differences existed after administration of GHRH and acute exercise. In Exp. 1, 10-min blood samples were collected from 12 mares for 8 h, and GHRH (0, 45, 90, or 180 micrograms) was administered at 6 h. In Exp. 2, 15-min blood samples were collected for 4 h from 10 mares, stallions, and geldings. In Exp. 3, eight horses of each sexual status were administered GHRH at 0900; later that day, each horse was exercised for 5 min. Blood samples were collected every 10 min around each event. In Exp. 1, prolactin concentrations decreased (P < .01) over the 8-h period, and there was an average of 2.9 +/- .5 episodes of increased secretion during that time; there was no correlation between these episodes and those in GH secretion. Prolactin concentrations were not affected (P > .1) by GHRH. In Exp. 2, average concentrations of GH were 2.4, 8.6, and 8.5 ng/mL for mares, stallions, and geldings, respectively; males differed from females (P < .05). Stallions and geldings had more (P < .05) peaks in GH concentrations and greater (P < .05) amplitude of peaks than mares. In contrast, prolactin concentrations were greater (P < .02) in mares and stallions than in geldings. In Exp. 3, GH response to GHRH was greater (P < .03) in stallions than in mares or geldings.(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1994-11-01 PubMed ID: 7730185DOI: 10.2527/1994.72112911xGoogle Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study investigates the relationship and reactions between the hormones prolactin and growth hormone (GH) in horses of different sexes, and how these reactions are affected by exercise and administration of growth hormone-releasing hormone (GHRH).
Study Overview
- Three experiments were conducted with different objectives aimed at understanding the relationship between hormone levels, the sex of the horse, and certain stimuli such as exercise and administering GHRH.
- In the first experiment, testing focused on the response of mares to GHRH and the relationship between prolactin and GH secretion.
- The second experiment was designed to compare GH and prolactin concentrations in the plasma of mares, stallions, and geldings.
- The third experiment examined the hormonal response of horses to GHRH administration and physical exercise within a day.
Findings from Experiment 1
- Over the 8 hours of testing, prolactin levels in the mares tested decreased consistently.
- The study detected an average of 2.9 increases in prolactin secretion over the same period, but these episodes did not correlate with similar changes in GH secretion.
- The administration of GHRH did not significantly affect prolactin concentrations.
Findings from Experiment 2
- GH concentrations varied among the three horse genders tested – mares had the lowest average levels, while stallions and geldings had higher averages.
- Compared to the mares, the stallions and geldings had more peaks in GH concentration and the peaks had a greater amplitude.
- Prolactin concentrations were, in contrast, higher in mares and stallions compared to geldings.
Findings from Experiment 3
- When GHRH was administered, the GH response was greater in stallions as compared to mares and geldings.
- These results suggest that sex may play a role in how horses respond to GHRH, with stallions showing a stronger response than the other two groups.
Implications and Further Research
- This study provides valuable insights into the hormonal responses of horses, revealing differences based not only on the hormone in question but also the sex of the horse.
- Further research is needed to fully understand the implications of these hormonal differences, such as how they might affect physical performance or reproductive behavior.
Cite This Article
APA
Thompson DL, DePew CL, Ortiz A, Sticker LS, Rahmanian MS.
(1994).
Growth hormone and prolactin concentrations in plasma of horses: sex differences and the effects of acute exercise and administration of growth hormone-releasing hormone.
J Anim Sci, 72(11), 2911-2918.
https://doi.org/10.2527/1994.72112911x Publication
Researcher Affiliations
- Department of Animal Science, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803.
MeSH Terms
- Analysis of Variance
- Animals
- Female
- Growth Hormone / blood
- Growth Hormone / metabolism
- Growth Hormone-Releasing Hormone / pharmacology
- Horses / blood
- Horses / metabolism
- Horses / physiology
- Male
- Physical Conditioning, Animal / physiology
- Prolactin / blood
- Prolactin / metabolism
- Sex Characteristics
- Time Factors
Citations
This article has been cited 4 times.- Kitaura T, Sato F, Hada T, Ishimaru M, Kodama R, Nambo Y, Watanabe G, Taya K. Influence of exercise and emotional stresses on secretion of prolactin and growth hormone in Thoroughbred horses. J Equine Sci 2021 Jun;32(2):49-53.
- Ferlazzo A, Cravana C, Fazio E, Medica P. The different hormonal system during exercise stress coping in horses. Vet World 2020 May;13(5):847-859.
- Kiełbik P, Witkowska-Piłaszewicz O. Iron Status in Sport Horses: Is It Important for Equine Athletes?. Int J Mol Sci 2025 Jun 12;26(12).
- Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K. Effect of birth month on endocrine function in Thoroughbred foals born in Hokkaido, the northern part of Japan. J Vet Med Sci 2025 Jul 7;87(7):804-815.
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