Changes in follicular fluid steroids, insulin-like growth factors (IGF) and IGF-binding protein concentration, and proteolytic activity during equine follicular development.

This research studies the changes in the equine (horse) follicular fluid’s insulin-like growth factor binding protein (IGFBP) proteolytic activity and other major component concentrations during follicular development in mares. The findings demonstrate that fluctuation in IGFBP levels might alter IGF activity, which may stimulate steroid production and cell division in growing horse follicles.

Objective of the Research

• The primary aim of this study is to measure changes in the IGFBP proteolytic activity, as well as the concentrations of various elements such as steroids, IGF, and IGFBP during follicular development in mares.

Research Methodology

• Fourteen mares were categorized based on whether they were in the follicular phase (8 mares) or the luteal phase (6 mares). They evaluated 92 follicles, which were classified as small, medium, or large. They then collected the follicular fluid.
• They observed that the estradiol and androstenedione levels within the follicular fluid tended to be greater in larger follicles, whereas the IGFBP-2, -4 and -5 concentrations were lesser.
• The IGFBP proteolysis was evaluated by checking the impact of follicular fluid on the human 125I-labeled IGFBP. They also analyzed the varying protease reactions concerning different IGFBP types within follicles of different sizes and phases.
• The IGFBP protease was then inhibited using specific protease inhibitors.
• Evaluations and comparisons were conducted using statistical analysis to determine correlations and distinctions in IGFBP concentrations and proteolysis activity.

Key Findings

• The researchers found that larger follicles had statistically greater levels of estradiol and androstenedione. They also demonstrated an increased level of IGFBP-3 and reduced concentrations of IGFBP-2, -4, and -5 compared to smaller or medium follicles.
• Estradiol and androstenedione concentrations turned out to be negatively associated with IGFBP-2, -4, and -5 but showed no correlation with IGFBP-3 concentrations.
• Follicular fluid, particularly from larger follicles collected during the follicular phase, showed more proteolytic activity on 125I-labelled IGFBP-5 than on IGFBP-2 or -3, indicating the presence of a specific protease within estrogen-dominant follicles.
• In conclusion, the changes in IGFBP-5 levels could be attributed to the varying protease activities, impacting IGF bioavailability, steroidal production, and cell division within equine follicles.