Response of the hypothalamic-pituitary-adrenal axis to stimulation tests before and after exercise training in old and young Standardbred mares.
Abstract: This study tested the hypotheses that age-induced alteration in cortisol, ACTH, and glucose concentrations are due to differences in the response of the hypothalamic-pituitary-adrenal axis and that exercise training would attenuate these differences. Six old (22.0±0.7 yr; mean±SE) and 6 young (7.3±0.6 yr) unfit Standardbred mares ran 3 graded exercise tests (GXT): before (GXT1), after 8 wk of training (GXT2), and at study end at 15 wk (GXT3). Mares trained 3 d/wk at 60% maximum heart rate. Each mare underwent 5 endocrine stimulation tests pre- and posttraining: 1) control (CON), 2) adrenocorticotropin hormone (ACTHtest), 3) combined dexamethasone suppression/ACTH (DEX/ACTH), 4) dexamethasone suppression (DEX), and 5) combined DEX/corticotropin releasing factor (DEX/CRF). For CON, there was no difference in plasma cortisol between age groups pretraining (P=0.19), but young mares had a 102% higher mean (P=0.02) plasma cortisol concentration than old mares posttraining. The pretraining ACTHtest showed young mares had a 72% higher (P=0.05) overall plasma cortisol concentration compared to old. There was no overall age difference in cortisol in the posttraining ACTHtest, but old mares still had lower cortisol concentrations at 30 min during the test, suggesting decreased adrenal response to ACTH stimulation. There was no difference in cortisol response between old and young mares in DEX, DEX/ACTH, or DEX/CRF tests. Young mares had higher (P=0.02) overall plasma cortisol concentration posttraining in response to DEX/ACTH, but old mares showed no change. In CON and DEX/CRF, there were no age differences in plasma ACTH concentration, pre- or posttraining. Pretraining, there was no age difference in glucose response to DEX, but posttraining old mares had a 4% (P=0.04) lower overall plasma glucose concentration compared to young. Posttraining, old mares had lower mean plasma glucose concentrations during DEX compared to pretraining (P=0.02), but there was no change pre- vs. posttraining in young mares (P=0.19). Old and young mares had lower plasma glucose concentrations posttraining during DEX/ACTH (P<0.001 and P=0.05, respectively) and DEX/CRF (P<0.001 and P=0.003, respectively) compared to pretraining. Both the pituitary and adrenal glands experience a decline in function with age although the exact mechanisms behind such changes remain unknown. Exercise training facilitates the counteraction of these deficits.
Publication Date: 2013-09-17 PubMed ID: 24045480DOI: 10.2527/jas.2013-6329Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research analyzes how age and physical training impact the hormonal response to stress in Standardbred mares, particularly focusing on cortisol, ACTH, and glucose levels.
Study Overview
- This study tested two hypotheses – the variation in cortisol, ACTH (Adrenal Corticotropic Hormone), and glucose levels triggered by aging are due to differing responses of the hypothalamic-pituitary-adrenal axis; and that physical training could lessen these variations.
- Two groups of six Standardbred mares each, categorised based on age as ‘old’ (average 22 years) and ‘young’ (average 7.3 years), were the subjects of the study.
- The horses ran three graded exercise tests (GXT) – before training (GXT1), after 8 weeks of training (GXT2), and at the end of the study at 15 weeks (GXT3). The training regimen consisted of three days per week at 60% maximum heart rate.
Endocrine Stimulation Tests
- The mares underwent five endocrine stimulation tests before and after training, these were: the control (CON), ACTH hormone (ACTHtest), a combined dexamethasone suppression/ACTH (DEX/ACTH), dexamethasone suppression alone (DEX), and a combined DEX/corticotropin-releasing factor (DEX/CRF).
- These tests were designed to measure the horses’ hormonal responses to different types of stimuli or suppressions.
Findings & Implications
- Before training, there wasn’t a significant difference noted in cortisol levels between the two age groups. However, after training, young mares had a significantly higher mean plasma cortisol concentration than older mares.
- In ACTH tests conducted pre-training, young mares had overall higher cortisol concentration compared to old ones. No overall age difference in cortisol was observed in ACTH tests post-training, but the old mares had lower cortisol concentrations 30 minutes during the test, indicating a decreased adrenal response to ACTH stimulation.
- No difference in cortisol responses between old and young mares was observed in DEX, DEX/ACTH, or DEX/CRF tests. However, young mares had a higher overall cortisol concentration post-training in the DEX/ACTH test.
- Regarding glucose response, old mares had a slightly lower overall plasma glucose concentration after training compared to young ones. Both old and young mares had lower glucose concentrations post-training during DEX/ACTH and DEX/CRF as compared to pre-training.
- The results indicate that age results in a decline in pituitary and adrenal gland function, but the exact mechanisms are unknown. The study also found that physical training can mediate this decline.
Cite This Article
APA
Liburt NR, McKeever KH, Malinowski K, Smarsh DN, Geor RJ.
(2013).
Response of the hypothalamic-pituitary-adrenal axis to stimulation tests before and after exercise training in old and young Standardbred mares.
J Anim Sci, 91(11), 5208-5219.
https://doi.org/10.2527/jas.2013-6329 Publication
Researcher Affiliations
- Equine Science Center, Rutgers, The State University of New Jersey, New Brunswick 08901.
MeSH Terms
- Adrenocorticotropic Hormone / administration & dosage
- Adrenocorticotropic Hormone / pharmacology
- Aging
- Animals
- Blood Glucose
- Corticotropin-Releasing Hormone / administration & dosage
- Corticotropin-Releasing Hormone / pharmacology
- Dexamethasone / administration & dosage
- Dexamethasone / pharmacology
- Female
- Horses / physiology
- Hydrocortisone / blood
- Hypothalamo-Hypophyseal System / physiology
- Physical Conditioning, Animal / physiology
- Pituitary-Adrenal System / physiology
- Time Factors
Citations
This article has been cited 3 times.- Horn R, Stewart AJ, Jackson KV, Dryburgh EL, Medina-Torres CE, Bertin FR. Clinical implications of using adrenocorticotropic hormone diagnostic cutoffs or reference intervals to diagnose pituitary pars intermedia dysfunction in mature horses. J Vet Intern Med 2021 Jan;35(1):560-570.
- Cravana C, Medica P, Fazio E, Satué K, Brancato G, La Fauci D, Bruschetta G. Circulating ACTH and Cortisol Investigations in Standardbred Racehorses Under Training and Racing Sessions. Vet Sci 2025 May 19;12(5).
- Giers J, Bartel A, Kirsch K, Müller SF, Horstmann S, Gehlen H. Blood-based assessment of oxidative stress, inflammation, endocrine and metabolic adaptations in eventing horses accounting for plasma volume shift after exercise. Vet Med Sci 2024 May;10(3):e1409.
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