Differential profiles of GH, IGF-1, and fructosamine in follicular fluid and plasma of cyclic mares.

Overview

• This study investigated the levels of growth hormone (GH), insulin-like growth factor 1 (IGF-1), and fructosamine (FRUCT) in the plasma and follicular fluid (FF) of mares at different stages of follicle development to understand their roles in follicular growth and metabolism.

Research Context

• GH is known to influence follicle development mainly by stimulating IGF-1 production.
• IGF-1 acts both systemically in the blood and locally within the ovarian follicles to support follicle growth.
• Fructosamine (FRUCT) is a biochemical marker that indicates glucose metabolism over time; however, its profile in the follicular fluid of mares was not well understood prior to this study.

Aims of the Study

• To measure and compare the concentrations of GH, IGF-1, and FRUCT in the plasma and follicular fluid of mares.
• To assess how these concentrations vary according to the size of ovarian follicles classified as small (20-30 mm), medium (31-40 mm), or large (≥41 mm).
• To explore correlations between these factors to better understand the metabolic and hormonal environment within developing follicles.

Methods

• Samples were collected from 30 clinically normal mares during the breeding season.
• Sixty ovaries were obtained post-slaughter, and follicles were size-classified into small, medium, and large categories.
• Blood samples were collected from the mares prior to slaughter for plasma analysis.
• Follicular fluid was meticulously aspirated from individual follicles for analysis.
• GH was quantified using enzyme immunoassay.
• IGF-1 levels were measured by ELISA (enzyme-linked immunosorbent assay).
• FRUCT concentrations were determined through spectrophotometry.

Key Findings

• GH concentrations showed no significant differences between plasma and follicular fluid regardless of follicle size, indicating a stable level of GH both systemically and locally.
• IGF-1 levels remained low in both plasma and FF for small and medium follicles but significantly increased in large, preovulatory follicles, suggesting its involvement in the final stages of follicular maturation.
• FRUCT concentrations in the follicular fluid gradually increased as follicles grew larger, consistently surpassing plasma levels, which points to enhanced local carbohydrate metabolism within larger follicles.
• A positive correlation (r = 0.65) was found between IGF-1 and FRUCT levels, suggesting a link between metabolic activity (glucose metabolism) and growth signaling within the follicular environment.

Interpretation and Implications

• IGF-1 likely plays a critical role in the final maturation of ovarian follicles, supporting the development of follicles ready for ovulation.
• The increasing fructosamine concentration in follicular fluid reflects enhanced carbohydrate metabolism as follicles grow, which might help meet the energy demands of growing follicles.
• The correlation between IGF-1 and fructosamine suggests that metabolic changes within the follicle support hormonal pathways that govern growth and maturation.
• These insights improve the understanding of equine ovarian follicle physiology, which could impact reproductive management in mares, especially those used in breeding or production.