A specific adenylyl cyclase inhibitor (DDA) and a cyclic AMP-dependent protein kinase inhibitor (H-89) block the action of equine growth hormone on in vitro maturation of equine oocytes.

The research study investigates the role of equine growth hormone in the in vitro maturation of horse eggs, and how specific inhibitors can impact the process. The findings conclude that the growth hormone does affect egg maturation, and its impacts can be blocked by certain inhibitors.

Study Objectives and Set Up

• The study primarily aimed to investigate if the stimulatory effect of equine Growth Hormone (eGH) on equine oocyte (horse egg) maturation in the lab was mediated through a molecular messenger called cyclic adenosine monophosphate (cAMP).
• The secondary objective was to find out if additional eGH in the lab influenced oocyte nuclear maturation, and whether this effect could be negated with Growth Hormone inhibitors.

Methodology

• Cumulus-Oocyte Complexes (COCs) were obtained from follicles smaller than 25mm in diameter. These complexes were randomly assigned either to a control group (no additives) or a group treated with eGH.
• To examine if the effect of eGH can be blocked, two inhibitors were employed: H-89, a cyclic AMP-dependent protein kinase inhibitor and 2′,3′-dideoxyadenosine (DDA), a specific adenylate cyclase inhibitor.
• The COCs were cultured for 30 hours at 38.5°C with 5% CO2 in air, after which they were stained with a Hoechst dye to assess the status of the nucleus.

Results and Conclusion

• COCs treated with eGH yielded a significantly higher proportion of mature oocytes compared to the control group, indicating that eGH does stimulate in vitro oocyte maturation.
• This effect, however, was diminished when the COCs were treated with either H-89 or DDA. The number of oocytes that reached maturity was significantly reduced when the inhibitors were used at certain concentrations, as compared to the eGH group.
• This finding confirms that the stimulatory effect of eGH can be blocked and suggests that eGH’s effect on oocyte maturation is mediated through a cAMP-dependent pathway.