Seasonal effects on the response of ovarian follicles to IGF1 in mares.

This research investigates how the response of ovarian follicles to Insulin-like Growth Factor 1 (IGF1) in horses changes between the transition into the breeding season and the breeding period itself. It showed that the size of the follicles does matter in terms of IGF1 response and this response differed between transitional and breeding seasons.

Methodology

• The researchers conducted a cross-over experiment on eight mares, studying their responses to IGF1 between the transition into the ovulatory season (transitional period) and the ovulatory season (ovulatory period) itself.
• Granulosa cells from the ovarian follicles of each mare were collected at two different size stages (15-24 mm and 25-34 mm).
• The expression levels of IGF1R, IGF2R, FSHR, LHCGR, and PAPPA were determined through quantitative PCR. These indicators are all associated with ovarian function.
• IGF1 was injected into the largest follicle during the transitional period and the second largest during the ovulatory period. The follicular fluid was then collected 24 hours after injection for analysis.

Results

• It was found that granulosa cells in follicles of the 25-34 mm size range, but not those in the 15-24 mm range, expressed higher levels of IGF1R, FSHR, and LHCGR during the ovulatory period than during the transitional period.
• IGF2R expression was higher in follicles during the transitional period than the ovulatory season.
• No significant difference was recorded in IGFBP2 levels between the two periods and treatments. However, IGFBP5 levels were higher during the ovulatory period.
• Injection of IGF1 before the differentiation of follicle sizes resulted in a roughly twofold increase in follicular inhibin A levels in both periods. However, it did not influence oestradiol levels.

Conclusion

• The results suggest that follicles are responsive to IGF1 before the differentiation in follicle sizes, both during ovulatory waves and transitional waves.
• This result indicates that deficient IGF1 response before follicle differentiation may not contribute to the impaired development of dominant follicles during the transitional period.