In vivo effects of pregnancy-associated plasma protein-A, activin-A and vascular endothelial growth factor on other follicular-fluid factors during follicle deviation in mares.

The research demonstrates the role of pregnancy-associated plasma protein-A (PAPP-A), IGF-I, activin-A, and vascular endothelial growth factor (VEGF) in the process of follicular deviation in mares. The results show that these factors influence the concentrations of various other elements present in follicular fluid, thereby impacting the growth and development of follicles.

Study Design and Procedure

• The research involved studying the intrafollicular effects of four factors – PAPP-A, IGF-I, activin-A, and VEGF – during the phenomenon of follicular deviation in mares. In this context, deviation refers to the point at which the two largest follicles (labelled as F1 and F2) start to diverge in size, typically when the size of F1 reaches a mean of 22.5 mm.
• In the experiment, four treatments were administered, with each involving a single dose of one of the four factors. These were injected into F2 when F1 had grown to at least 20.0 mm, which is considered the expected beginning of the deviation. A control group was also maintained, in which F2 was given a vehicle injection.
• Follicular fluid samples were obtained from the control and treated groups a day after the treatment and subjected to assays for measuring free IGF-I, oestradiol, androstenedione, activin-A, inhibin-A, follistatin, and VEGF present.

Key Findings

• Within the control group, all end points were significantly higher in the leading follicle F1 compared to the subordinate F2, with the exception of androstenedione concentration, which was lesser in F1.
• Administration of PAPP-A in F2 led to increased concentrations of free IGF-I, inhibin-A, follistatin, and VEGF and reduced levels of androstenedione.
• IGF-I treatment resulted in an upsurge of inhibin-A and a decrease in androstenedione concentrations in the follicular fluid.
• Activin-A lowered the concentrations of follistatin and androstenedione, while increasing the size of the F2 follicle.
• VEGF administration led to an increase in IGF-I and a decrease in androstenedione concentrations.

Conclusions

• The results supported the hypothesis that during follicular deviation in mares, PAPP-A increases the follicular fluid concentrations of free IGF-I, the production of follistatin responds to changes in concentrations of activin-A, and VEGF impacts other follicular fluid factors’ concentrations.
• This study ultimately sheds light on the complex intrafollicular dynamics that occur during follicle deviation and the key role that these examined factors play in the process.