Influence of equine growth hormone, insulin-like growth factor-I and its interaction with gonadotropins on in vitro maturation and cytoskeleton morphology in equine oocytes.

The researchers studied the effects of equine growth hormone (eGH) and insulin-like growth factor-I (IGF-I), as well as their interaction with gonadotropins, on the in vitro maturation of horse oocytes. They found that using eGH, E2, gonadotropins, and FCS increased the number of oocytes reaching maturation.

Objective of the Study

• The main objective of this research was to investigate the effects of equine growth hormone (eGH) and insulin-like growth factor-I (IGF-I) as well as the role of estradiol (E2), gonadotropins (FSH and LH) and fetal calf serum (FCS) in promoting in vitro maturation (IVM) of horse oocytes. Beyond these factors, the researchers also aimed to evaluate the cytoskeleton organization of horse oocytes after IVM with eGH.

Methodology

• The researchers aspirated equine oocytes from follicles smaller than 30 mm in diameter and matured them for 30 hours at 38.5 degrees Celsius in an atmosphere with 5% CO2.
• The selected cumulus-oocyte complexes (COCs) were allocated to five different experimental groups: a control group with no additives, a group with eGH, a group with IGF-I, a group with both eGH and IGF-I, and a group with eGH, IGF-I, and an anti-IGF-I substance. Additionally, some groups were also treated with E2, FSH, LH, and FCS.
• The oocytes were stained with markers for microtubules, microfilaments, and chromatin and then examined under a confocal microscope.

Results of the Study

• There were no observable differences when eGH and IGF-I were added to the IVM system. However, the study found a significant increase in the maturation of oocytes when they were incubated with eGH alone or with the combined application of eGH, E2, gonadotropins, and FCS.
• The matured equine oocytes revealed a thin filament network concentrated within the oocyte cortex and microtubules at the metaphase spindle displayed a symmetrical barrel-shaped structure, with chromosomes lined up along its center.

Conclusion

• The researchers concluded that the use of eGH in the presence of E2, gonadotropins, and FCS increases the number of oocytes reaching maturation, suggesting a potential methodology for improving in vitro maturation of horse oocytes. This might help to overcome current limitations in successful in vitro fertilization procedures in horses.