Effect of number and diameter of follicles on plasma concentrations of inhibin and FSH in mares.
Abstract: The role of the number of follicles and circulating immunoreactive inhibin in the decrease in plasma FSH concentrations that occurs during development of a follicular wave was studied in mares. All follicles > or = 6 mm in diameter were ablated by ultrasound-guided transvaginal aspiration of follicular fluid on day 10 after ovulation. During the subsequent wave, all follicles, the three largest follicles (three follicle group), the largest follicle (single follicle group) or no follicles were retained and the remaining follicles were ablated before they reached > 10 mm in diameter (n = 10-11 mares per group). Ablation of new follicles was continued until the day on which the largest follicle of the new wave reached 25 mm in diameter (day 18 after ovulation in the 'no follicle' group). Diameters of retained follicles were measured once a day by transrectal ultrasonography. Plasma samples were taken once a day and analysed by radioimmunoassay for concentrations of FSH and immunoreactive inhibin (includes dimeric inhibin as well as free alpha-subunit forms). Data were normalized to the day of the expected start of the decrease in plasma FSH concentrations (day 0: largest follicle 13 mm in diameter in the follicle-retained groups). A simultaneous increase in circulating concentrations of FSH (P < 0.05) and immunoreactive inhibin (P < 0.05) occurred before the largest follicle reached 13 mm in diameter, which indicates that immunoreactive inhibin produced by follicles < 13 mm in diameter did not suppress FSH. Plasma concentrations of FSH decreased (P < 0.05) and immunoreactive inhibin concentrations increased (P < 0.05) after day 0 in the follicle-retained groups. A slower decrease in FSH concentrations was associated temporally with a delay in the increase in immunoreactive inhibin concentrations in the 'single follicle' group relative to the 'three follicle' and 'all follicle' groups. All follicle-retained groups had similar plasma concentrations of FSH and immunoreactive inhibin after the expected beginning of deviation in growth rates between the two largest follicles (largest follicle 22-23 mm in diameter). These results indicated that the decrease in plasma FSH concentrations from the start of the decrease until the expected day of deviation was a function of multiple follicles of a wave and was attributable to the secretion of inhibin. Thereafter, the largest follicle alone accounted for the continued FSH suppression.
Publication Date: 2001-05-25 PubMed ID: 11373176
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research article explores the effect of the number and size of follicles on the plasma concentrations of inhibin and FSH in mares. The study reveals that the decrease in plasma FSH concentrations during the development of a follicular wave is due to multiple follicles secreting inhibin.
Study Design and Methodology
- The study was carried out on mares, focusing on the role of the number of follicles and circulating immunoreactive inhibin in reducing plasma FSH concentrations during the development of a follicular wave.
- The follicles with a diameter greater than or equal to 6mm were ablated on the 10th day after ovulation.
- Throughout the subsequent wave, every follicle, the three largest follicles, the largest follicle, or no follicles were maintained, while the other follicles were ablated before growing larger than 10mm in diameter.
- This ablation process continued until the largest follicle of the new wave had a diameter of 25mm. The diameters of retained follicles were measured daily.
- Plasma samples were also taken daily and analysed for concentrations of FSH and immunoreactive inhibin.
Results
- The study found that the concentration of FSH and immunoreactive inhibin in circulating blood increased before the largest follicle reached a diameter of 13mm.
- This suggests that immunoreactive inhibin produced by follicles smaller than 13mm in diameter did not suppress FSH.
- Plasma concentrations of FSH decreased and inhibin concentrations increased after that period in the groups retaining follicles.
- The ‘single follicle’ group experienced a slower decrease in FSH concentration, alongside a delay in the increase in inhibin concentration, compared to the ‘three follicle’ and ‘all follicle’ groups.
- All the groups retaining follicles had similar plasma concentrations of FSH and inhibin once the growth rates began to deviate between the two largest follicles.
Conclusions
- Overall, the findings indicate that the decrease in plasma FSH concentrations from the start of the decrease until the expected day of deviation was due to the secretion of inhibin from multiple follicles of a wave.
- Following this point, it was found that the largest follicle alone accounted for the continued suppression of FSH.
Cite This Article
APA
Donadeu FX, Ginther OJ.
(2001).
Effect of number and diameter of follicles on plasma concentrations of inhibin and FSH in mares.
Reproduction, 121(6), 897-903.
Publication
Researcher Affiliations
- Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, WI 53706, USA. donadeu@ahabs.wisc.edu
MeSH Terms
- Animals
- Female
- Follicle Stimulating Hormone / blood
- Follicular Fluid
- Horses / physiology
- Inhibins / blood
- Kinetics
- Ovarian Follicle / anatomy & histology
- Ovarian Follicle / diagnostic imaging
- Ovarian Follicle / physiology
- Ovulation
- Suction
- Ultrasonography
Citations
This article has been cited 2 times.- Ginther OJ, Beg MA, Gastal EL, Gastal MO, Baerwald AR, Pierson RA. Systemic concentrations of hormones during the development of follicular waves in mares and women: a comparative study. Reproduction 2005 Sep;130(3):379-88.
- Medan MS, Nambo Y, Nagamine N, Shinbo H, Watanabe G, Groome N, Taya K. Plasma concentrations of ir-inhibin, inhibin A, inhibin pro-alphaC, FSH, and estradiol-17beta during estrous cycle in mares and their relationship with follicular growth. Endocrine 2004 Oct;25(1):7-14.
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