Functional relationships among intrafollicular insulin-like growth factor 1, circulatory gonadotropins, and development of the dominant follicle in mares.
Abstract: The functional relationships among intrafollicular free insulin-like growth factor 1 (IGF1), circulatory gonadotropins, and development of the dominant follicle were studied in 40 mares in two experiments. A GnRH antagonist (Acyline) was given i.m. at the expected beginning of follicular deviation (largest follicle or F1> or =20mm; Day 0) alone (Acyline group) or in combination with intrafollicular treatment of F1 with rhIGF1 (Acyline/IGF1 group). In Experiment 1, blood samples, follicular-fluid samples, and diameter of F1 were taken on Days 1 and 2. In Experiment 2, daily follicular diameter and blood samples were taken from Day 0 to ovulation. The GnRH antagonist induced a 50% decrease in circulatory FSH concentrations for 1 d and in LH for 2 d. In Experiment 1, control and Acyline/IGF1 groups had greater intrafollicular free IGF1 (P<0.05) and inhibin-A concentrations (P<0.08) than the Acyline group. The intrafollicular concentration of estradiol on Day 2 was greater (P<0.05) in the control group than in the Acyline and the Acyline/IGF1 groups. In Experiment 2, a decrease in diameter of F1 in the Acyline group was followed by a new follicular wave. All IGF-treated follicles grew and ovulated. Results indicated that the increase in intrafollicular free IGF1 observed in F1 in association with deviation is gonadotropin dependent. During the period of lesser gonadotropin concentrations from Acyline treatment, intrafollicular IGF1 stimulated follicular growth and inhibin concentrations, but not intrafollicular estradiol production.
Copyright 2009 Elsevier B.V. All rights reserved.
Publication Date: 2009-09-30 PubMed ID: 19864088DOI: 10.1016/j.anireprosci.2009.09.002Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research examines the relationships between a growth factor found in follicles, hormones that stimulate the growth and development of eggs in mares, and the development of dominant follicles. The results showed that the growth and ovulation of dominant follicles are dependent on both the presence of these hormones and the growth factor.
Research Methodology
- The researchers conducted two experiments to study the interactions between insulin-like growth factor 1 (IGF1) found inside follicles, hormones that stimulate egg growth and development called gonadotropins, and the development of dominant follicles in horse ovaries.
- These experiments involved treating 40 mares with a class of drugs known as GnRH antagonists (specifically Acyline) and monitoring various indicators such as blood and follicular-fluid samples, and follicle diameters.
- In the first experiment, the researchers took measurements on two consecutive days.
- In the second experiment, they took daily measurements from the start of treatment until the eggs were released.
Findings
- The researchers discovered that the GnRH antagonist caused a 50% reduction in the concentrations of two gonadotropins, FSH and LH. This reduction lasted for one day for FSH and two days for LH.
- In comparison to the group treated solely with Acyline, the control group and the group treated with Acyline/IGF1 exhibited higher concentrations of free IGF1 and inhibin-A in their follicles.
- The control group also had a larger concentration of estradiol in the follicles on the second day compared to the other two groups.
- In the second experiment, the researchers noticed that after treatment with Acyline, the diameter of dominant follicles in the treated group decreased, followed by the emergence of a new follicular wave. However, all follicles that received IGF treatment grew and ovulated.
Interpretation
- The results indicated that the increase in the amount of free IGF1 in the dominant follicle that coincides with follicle deviation is dependent on the gonadotropins.
- Lower gonadotropin levels due to Acyline treatment could be compensated by the presence of intrafollicular IGF1, stimulating follicle growth and the concentration of inhibin, but not the production of estradiol within the follicle.
Cite This Article
APA
Checura CM, Beg MA, Parrish JJ, Ginther OJ.
(2009).
Functional relationships among intrafollicular insulin-like growth factor 1, circulatory gonadotropins, and development of the dominant follicle in mares.
Anim Reprod Sci, 118(2-4), 270-278.
https://doi.org/10.1016/j.anireprosci.2009.09.002 Publication
Researcher Affiliations
- Eutheria Foundation, Cross Plains, WI 53528, USA.
MeSH Terms
- Animals
- Female
- Follicle Stimulating Hormone / blood
- Gonadotropin-Releasing Hormone / antagonists & inhibitors
- Horses / physiology
- Inhibins / analysis
- Insulin-Like Growth Factor I / analysis
- Insulin-Like Growth Factor I / physiology
- Luteinizing Hormone / blood
- Oligopeptides / administration & dosage
- Ovarian Follicle / chemistry
- Ovarian Follicle / diagnostic imaging
- Ovarian Follicle / growth & development
- Ultrasonography
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