Secretion of luteinizing hormone into pituitary venous effluent of the follicular and luteal phase mare: novel acceleration of episodic release during constant infusion of gonadotropin-releasing hormone.
Abstract: We tested the hypothesis that continuous infusion of native GnRH into mares during the estrous cycle, at a dose of 100 μg/h, would elevate circulating concentrations of LH without disrupting the endogenous, episodic pattern of LH release. Ten cyclic mares were assigned to one of two groups (n = 5/group): (1) Control (saline) and (2) GnRH in saline (100 μg/h). On experimental day 0 (3 to 6 d after ovulation), osmotic pumps containing saline or GnRH were placed subcutaneously and connected to a jugular infusion catheter. Blood samples were collected from jugular catheters daily and at 5-min intervals from catheters placed in the intercavernous sinus (ICS) for 8 h on experimental day 4 (luteal phase; 7 to 10 d after ovulation), followed by an additional 6-h intensive sampling period 36 h after PGF(2α)-induced luteal regression (experimental day 6; follicular phase). Treatment with GnRH increased (P < 0.001) concentrations of LH by 3- to 4-fold in the peripheral circulation and 4- to 5-fold in the ICS. Continuous GnRH treatment accelerated (P < 0.01) the frequency of LH release and decreased the interepisodic interval during both luteal and follicular phases. Treatment with GnRH during the luteal phase eliminated the low-frequency, long-duration pattern of episodic LH release and converted it to a high-frequency, short-duration pattern reminiscent of the follicular phase. These observations appear to be unique to the horse. Further studies that exploit this experimental model are likely to reveal novel mechanisms regulating the control of gonadotrope function in this species.
Copyright © 2012 Elsevier Inc. All rights reserved.
Publication Date: 2012-01-27 PubMed ID: 22305208DOI: 10.1016/j.domaniend.2012.01.004Google 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 continuous infusion of gonadotropin-releasing hormone (GnRH) on the levels and release patterns of luteinizing hormone (LH) in mares during their estrous cycle. The findings indicate that GnRH infusion significantly increases LH concentrations and alters its release patterns, revealing potential new insights into the regulation of gonadotrope function in horses.
Objective and Methodology
- The research aimed to verify the hypothesis that continuously infusing mares with gonadotropin-releasing hormone (GnRH) during their estrous cycle would increase the circulating levels of luteinizing hormone (LH) without changing the endogenous episodic pattern of LH release.
- The experiment included ten cyclic mares that were divided into two groups: those who received a saline control (group 1) and those who were administered 100 µg/h of GnRH in saline (group 2).
- On the experiment’s start day (3-6 days after ovulation), osmotic pumps containing either saline or GnRH were subcutaneously placed and linked to a jugular infusion catheter in the mares.
- Blood samples were collected from the jugular catheters daily. On the fourth day of the experiment (during the luteal phase of the cycle), additional samples were taken every five minutes from catheters placed in the intercavernous sinus (ICS) for an eight-hour period.
Key Results
- Treatment with GnRH led to a 3-4-fold increase in LH concentrations in the peripheral circulation and a 4-5-fold increase in the ICS.
- The frequency of LH release accelerated, and the interval between LH release episodes decreased in both the luteal and follicular phases.
- The GnRH treatment during the luteal phase changed the pattern of episodic LH release from a low-frequency, long-duration pattern to a high-frequency, short-duration pattern, similar to the follicular phase’s pattern.
- The effects observed in this study seem to be unique to horses, suggesting this study’s model can be useful for future research into regulatory mechanisms of gonadotrope function in horses.
Cite This Article
APA
Velez IC, Pack JD, Porter MB, Sharp DC, Amstalden M, Williams GL.
(2012).
Secretion of luteinizing hormone into pituitary venous effluent of the follicular and luteal phase mare: novel acceleration of episodic release during constant infusion of gonadotropin-releasing hormone.
Domest Anim Endocrinol, 42(3), 121-128.
https://doi.org/10.1016/j.domaniend.2012.01.004 Publication
Researcher Affiliations
- Animal Reproduction Laboratory, Texas AgriLife Research, Beeville, TX 78102-8571, USA.
MeSH Terms
- Animals
- Dinoprost / pharmacology
- Estrous Cycle / drug effects
- Estrous Cycle / metabolism
- Female
- Gonadotropin-Releasing Hormone / pharmacology
- Horses / metabolism
- Luteinizing Hormone / blood
- Luteinizing Hormone / metabolism
- Ovulation / blood
- Ovulation / drug effects
- Ovulation / physiology
- Pituitary Gland / blood supply
- Pituitary Gland / drug effects
- Pituitary Gland / metabolism
- Progesterone / blood
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