Effects of Time Specific Supplementation of Insulin Like Growth Factor-I (IGF-I) on in vitro Development of Sheep Preantral Follicles

Background: In in vitro culture systems IGF-I was known to promote follicular maturation, granulosa cell proliferation and increase overall cellular function. The expression patterns of developmentally important markers for IGF-I are expressed differentially during the transition of preantral follicles to the ovulatory stage. Therefore, we aimed to investigate the influence of time specific addition of Insulin like growth factor -I (IGF-I) on in vitro development of sheep preantral follicles (PFs'). Methods: Mechanically isolated sheep preantral follicles were cultured for six days either in TCM 199B or standard medium supplemented with IGF-I at different points during the culture period and were subsequently subjected to in vitro maturation (IVM) for additional 24 hrs to evaluate different follicular development parameters. Conclusion: Based on the results, it is concluded that: 1) IGF-I supplementation was needed during early rather than later stages of culture period, therefore, role of IGF-I in time/stage specific manner in cultured preantral follicles is confirmed. 2) Supplementation of TCM 199B with IGF-I simultaneously for the first two days followed by TCM 199B alone without any growth factor (s) in later days (Treatment 1) supported better development of PFs' in vitro.