Effect of LH and Estradiol-17β Supplementation at Different Time Points on In vitro Development of Preantral Follicles in Sheep

Abstract

Background: Ovarian follicular development and growth are controlled by many hormones and growth factors. Despite the fact that LH and estradiol-17β have been utilized for the in vitro culture of preantral follicles yet, the suitable time points of supplementation of LH and estradiol-17β is not known. Therefore this study aimed to investigate the influence of addition of LH and estradiol-17β at different time points on in vitro development of preantral follicles (PFs’) in sheep. Method: Preantral follicles isolated from the ovarian cortical slices using micro dissection method were cultured for six days in Bicarbonate buffered Tissue culture medium 199B (TCM 199B) or in a standard culture medium supplemented with LH (2 μg/ml) and estradiol-17β (5 ng/ml) at different points during the culture period. COCs isolated from the follicles at the end of six day culture in different treatments were subjected to in vitro maturation for additional 24h. Result: Supplementation of LH and estradiol-17β during last two days of the culture supported better proportion of PFs’ exhibiting growth whereas supplementation of LH and estradiol-17β during first two days of the culture supported better average increase in diameter and proportion of PFs’ exhibiting antrum formation at the end of six day culture. Further the oocytes in COCs isolated at the end of culture in these treatments and subsequently subjected to in vitro maturation (IVM) for 24hr developed at a higher frequency to MII (metaphase II) stage. Supplementation of LH and estradiol-17β to TCM 199B culture medium in early stages followed by standard medium alone in later stages supports better development of PFs’ in vitro. Following supplementation with LH and estradiol-17β for the first two days culture of PFs’ in standard medium appears to be advantageous for the development of preantral follicles in vitro.