STEROID-LEVEL RESPONSE TO INSULIN-LIKE GROWTH-FACTOR-I IN OOCYTES MATURED IN-VITRO

The objective was to establish the influence of insulin-like growth fa ctor-1 (IGF-1) on steroid production and nuclear maturation during ooc yte in vitro maturation (IVM). Immature-selected rabbit follicular ooc ytes, divided as cumulus-oocyte complexes (COC) and denuded oocytes (D O), were cultured in Brackett's medium with different concentrations o f IGF-1 at 0, 50, 100 and 200 ng/ml. After 8 and 16 h of culture, the oocytes were assessed for nuclear maturation by acetic-orcein stain, a nd media were analyzed by enzyme-immunoassay (EIA) for 17 beta-estradi ol (E), progesterone (P), androstenedione (A) and testosterone (T) con tent. After culture treatments with IGF-1 significantly increased (P < 0.01) the incidence of nuclear activation (germinal vesicle breakdown stage, GVBD) and nuclear maturation (metaphase II stage); maximum sti mulation occurred at 100 ng IGF-1/ml (86.9 vs. 49.3% in control). Comp ared to controls, the presence of IGF-1 in cultures was associated wit h a significant increase of E and A production by COCs (P < 0.01). How ever, P and T levels were not significantly influenced by the IGF-1. I n addition, positive correlations between E/T and E/A ratios and nucle ar maturation rates were only found in the IGF-1 treatments. Regarding the DOs, neither positive effects in nuclear maturation rates nor inc rease of steroid levels in culture were observed for any treatment. Th ese results suggest that: (1) IGF-1 had a significant effect on E and A production during oocyte maturation; (2) the addition of IGF-1 enhan ced nuclear maturation significantly in rabbit oocytes; and (3) all th ese effects are only possible in oocytes surrounded by cumulus cells. (C) 1997 Elsevier Science Ireland Ltd.