Title: IMPACT OF INSULIN CONCENTRATION ON In vitro MATURATION OF RABBIT OOCYTES.
Abstract: This study aimed to evaluate the effect of adding insulin hormone at different levels (0, 5, 10 and 15 µg/ml) to maturation medium with or without exogenous hormones (FSH, LH and E17β) on the in vitro maturation (IVM) of rabbit oocytes.Total of 20 New Zealand White (NZW) rabbit does (5.5-6mo of age and 2.5 -3 kg LBW) were used as oocyte donors.Oocytes were recovered from ovaries of slaughtered does using slicing technique.All oocytes with evenly granulated dark ooplasm were matured in TCM-199 supplemented with 6% bovine serum albumin.Eight types of TCM-199, four types without and other four with exogenous hormones supplemented with insulin (0, 5, 10 and 15 µg /ml) were used.Oocytes were fixed and stained for examination after 18 h at 38.5°C, 5% CO2 and high humidity as a maturation period.Results showed significant (P<0.05)effect of insulin supplementation on IVM of rabbit oocyte only in terms of oocytes reaching MI, TI+MII and degenerated ones.Percentage of mature oocytes reaching MII was improved by all insulin levels as compared to un-supplemented media (42.1-44.6 vs. 34.1%),but the differences were not significant.Percentage of oocytes reaching both TI+MII increased (P<0.05) with insulin supplementation at a level of 5 µg/ml showing the best (P<0.05)improvement on oocyte maturation (51.0%) as compared to other insulin levels (45.5-47.6%)or the control medium (39.5%).Nuclear maturation of rabbit oocytes was not affected significantly when FSH, LH and E2 were deleted from the maturation medium, but Percentage of oocytes reaching both T1+MII stages was enhanced in the presence of hormones during the maturation period regardless of whether oocytes were treated with insulin or not.Maturation rate in term of oocytes reaching T1+MII was affected significantly (P<0.05) by the interaction between insulin and hormonal addition, reflecting improved percentage of oocytes reaching both T1+MII stages by addition of all insulin levels to hormone-TCM-199 medium.In this respect, insulin addition at a level of 5µg/ml showed the best result (58.7%).In conclusion, the present study demonstrated that the supplementation of the maturation medium with insulin improves the in vitro maturation rate of rabbit oocytes when oocytes are maturated in a defined maturation medium with or without hormones (FSH, LH and E2).