The effect of endotoxin administration on the secretory dynamics of oxytocin in follicular phase mares: relationship to stress axis hormones.
Abstract: The primary aim of this study was to define the secretory dynamics of oxytocin and vasopressin in pituitary venous effluent from ambulatory horses during acute endotoxaemia, a stimulus that may release both hormones. Our secondary aim was to investigate the role of oxytocin in regulating adrenocorticotropic hormone (ACTH) secretion by comparing oxytocin, vasopressin, corticotropin-releasing hormone (CRH) and ACTH secretory profiles during endotoxaemia and by monitoring the ACTH response to oxytocin administration. Pituitary venous blood was collected nonsurgically continuously and divided into 1-min segments from eight follicular phase mares. Four mares were sampled for 30 min before and 3.5 h after receiving an i.v. infusion of bacterial endotoxin (TOX). Four control mares were sampled for 2.5 h without infusion of TOX. Another three follicular phase mares were given 5 U of oxytocin to replicate the peak response to TOX and pituitary blood collected every 1 min for 10 min before and 15 min after injection. Endotoxin raised the secretion rates of all hormones measured. All hormones were released episodically throughout the experiment, with TOX increasing the amplitude of peaks in each hormone. Peaks in oxytocin and vasopressin were coincident in each treated mare. Similarly, ACTH peaks were coincident with peaks of oxytocin and vasopressin in each treated mare, and with peaks of CRH in three mares. However, oxytocin administration did not affect ACTH secretion. We conclude that during endotoxaemia in horses: (i) oxytocin and vasopressin are secreted synchronously; (ii) oxytocin is unlikely to be acting as an ACTH secretagogue since inducing peak oxytocin concentrations observed during TOX does not raise ACTH; and therefore (iii) the close relationship between oxytocin and ACTH secretion is circumstantial and due to the fact that oxytocin secretion is concurrent with that of vasopressin, a proven ACTH secretagogue in horses.
Publication Date: 2002-07-18 PubMed ID: 12121490DOI: 10.1046/j.1365-2826.2002.00815.xGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study investigates how endotoxin, a component of certain bacteria, affects the secretion of hormones, particularly oxytocin and vasopressin, in horses. The research further explores if oxytocin plays any role in the release of the stress hormone adrenocorticotropic hormone (ACTH).
Research Methodology and Experiment
- The study was conducted on eight mares in their follicular phase, i.e., the stage of the menstrual cycle when the ovarian follicles mature.
- Four of the mares were given a controlled infusion of bacterial endotoxin, while the remaining four served as the control group and were not given the toxin.
- A third test was performed on three additional mares who were given oxytocin. The researchers aimed at replicating the peak response to endotoxin by administrating oxytocin to observe if it could stimulate ACTH hormone release.
- Blood was collected continuously from all test subjects, and hormone secretion levels were monitored before, during, and after the administration of endotoxin or oxytocin.
Findings and Conclusions
- Endotoxin was found to increase the secretion rates of all the hormones under study – oxytocin, vasopressin, corticotropin-releasing hormone (CRH), and ACTH.
- The hormones were released episodically throughout the experiment with endotoxin boosting the amplitude at peak secretion.
- At high secretion rates, oxytocin and vasopressin were found to be released simultaneously in each mare treated with endotoxin.
- ACTH secretion coincided with that of oxytocin and vasopressin, and with that of CRH secretion, in at least three tested mares.
- However, administrating oxytocin did not affect ACTH secretion. This indicates that despite being released at the same time, oxytocin is not likely to be a secretagogue (a substance that causes the secretion) for ACTH.
- The researchers concluded that the synchrony of oxytocin and ACTH secretions during endotoxemia in horses is circumstantial and related to the concurrent secretion of vasopressin, a validated ACTH secretagogue.
Cite This Article
APA
Alexander SL, Irvine CH.
(2002).
The effect of endotoxin administration on the secretory dynamics of oxytocin in follicular phase mares: relationship to stress axis hormones.
J Neuroendocrinol, 14(7), 540-548.
https://doi.org/10.1046/j.1365-2826.2002.00815.x Publication
Researcher Affiliations
- Department of Endocrinology, Christchurch Public Hospital, Christchurch, New Zealand. xtr120453@xtra.co.nz
MeSH Terms
- Adrenocorticotropic Hormone / metabolism
- Animals
- Body Temperature / drug effects
- Corticotropin-Releasing Hormone / metabolism
- Endotoxemia / chemically induced
- Endotoxemia / metabolism
- Endotoxins / pharmacology
- Female
- Follicular Phase / drug effects
- Follicular Phase / physiology
- Heart Rate / drug effects
- Horses
- Jugular Veins
- Oxytocin / metabolism
- Oxytocin / pharmacology
- Stress, Physiological / metabolism
- Vasopressins / metabolism
Citations
This article has been cited 2 times.- Elder E, Wong D, Johnson K, Robertson H, Marner M, Dembek K. Assessment of the hypothalamic-pituitary-adrenocortical axis function using a vasopressin stimulation test in neonatal foals. J Vet Intern Med 2023 Sep-Oct;37(5):1881-1888.
- Baskaran C, Plessow F, Silva L, Asanza E, Marengi D, Eddy KT, Sluss PM, Johnson ML, Misra M, Lawson EA. Oxytocin secretion is pulsatile in men and is related to social-emotional functioning. Psychoneuroendocrinology 2017 Nov;85:28-34.
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