The involvement of growth hormone in equine oocyte maturation, receptor localization and steroid production by cumulus-oocyte complexes in vitro.

This study explored the effects of equine growth hormone on horse oocyte (immature egg cell) development and maturation in the lab, including steroid production by adjoining cumulus cells, and the role and location of growth hormone receptors in the ovarian follicles of horses.

Research Methodology

• The study began by extracting cumulus-oocyte complexes (COCs) from the ovarian follicles of horses. These follicles were smaller than 30mm in diameter and sourced from ovaries obtained from the abattoir.
• These collected COCs were then visually assessed and separated into two groups: a control group and a test group, the latter being treated with a supplement of 400 ng/mL equine growth hormone (eGH).
• The propagation of cells was conducted over a 30-hour period in the presence of an air and 5% CO2 mixture at a constant temperature of 38.5°C.
• To examine the cellular structures and processes, both sets of COCs were stained with propidium iodide for illuminating DNA and with fluorescein isothiocyanate-labeled Lens culinaris agglutinin for highlighting specific carbohydrates present on the cell surface.
• Comparative evaluations were carried out using confocal microscopy for detailed insights, particularly concentrating on changes in chromatin configuration and the distribution of cortical granules.

Outcomes

• The test group, treated with eGH, exhibited higher rates of achieving metaphase II, an advanced stage of cell division, as compared to the control group.
• Higher levels of testosterone, progesterone, and estradiol were found in the culture medium of the eGH-treated group, but the concentration of androstenedione was not significantly different between the two groups.
• A critical observation was that the expression of the eGH-receptor gene was more significant in cumulus cells and COCs at the onset than at the conclusion of in-vitro maturation.
• Positive staining for the presence of eGH-receptor was observed in cumulus cells, the oocytes, and granulosa cells, indicating its active role in equine oocyte maturation.

Conclusion

Based on the experimental findings, inclusion of eGH in the maturation process increased cytoplasmic maturation rates and demonstrated a critical role in equine oocyte maturation. This could be attributed to the presence of eGH-receptors in ovarian follicles, which facilitated advanced cellular growth and maturation under the influence of eGH.