Critical role of insulin-like growth factor system in follicle selection and dominance in mares.

This study explores how the insulin-like growth factor system influences the selection and dominance of ovarian follicles in horses. Researchers reduced the levels of growth factors in the ovarian fluid by injecting a binding protein, which showed a noticeable effect on the growth and hormonal activity of the follicles.

Objective and Methodology

• The research aimed to understand the role of the insulin-like growth factor (IGF) system in the divergence of growth rates among follicles, known as follicle selection, in mares.
• To demonstrate this, researchers used an IGF binding protein (IGFBP-3) to lower the concentrations of IGFs in the follicular fluid.
• The IGF system was tampered with at the onset of expected deviation in a sample size consisting of controls, vehicle, and actual test subjects (those injected with IGFBP-3).

Experiment and Results

• Following the injection of IGFBP-3, samples of follicular fluid were collected and analyzed. It was observed that IGFBP-3 significantly reduced the concentration of free IGF-1, along with the levels of other hormones and growth factors such as estradiol, activin-A, inhibin-A, and vascular endothelial growth factor.
• Conversely, the concentration of androstenedione, a steroid hormone, increased.
• Post-injection, the diameter of the dominant follicle (F1) decreased while the subordinate follicle (F2) increased, indicating a shift in follicular dominance.
• The BP test group also showed a higher increase in circulating concentrations of FSH, a hormone responsible for the growth and maturation of ovarian follicles, which led to the enhanced growth of F2.

Significance

• The domination and ovulation from F1 occurred in fewer cases in the BP group than in the control and vehicle groups, with most mares in the BP group ovulating from F2.
• The results suggest that the IGF system significantly influences changes in the concentrations of follicular-fluid factors between the dominant and subordinate follicles, affecting the development of follicle dominance (selection) and ovulation in mares.
• This understanding has crucial implications in reproductive science, specifically in the study of follicular dominance and selection, fertility, and potential treatments for reproductive disorders.