Nowadays, though highly improved, the efficiency of human assisted reproduction protocols remains affected by a decrease in embryo yields after IVF. The aim of the current study was to evaluate a possible relationship between poor embryos and the functionality of follicles stimulated to grow with exogenous gonadotrophins, using a monovular species (sheep) as a model. In ewes, follicles can ovulate from ≥6 mm in unstimulated cycles, but from ≥4 mm in FSH treatments. Fourteen Manchega ewes were superovulated with a commonly used protocol, consisting of 8 step-down doses of oFSH (OVAGEN, ICP, New Zealand), twice daily during the last days of an intravaginal progestagen treatment. At oestrus detection, all preovulatory-sized follicles (≥4 mm, n=230) were dissected and both follicular fluid and oocytes were individually obtained. Follicular function was determined by measuring intrafollicular concentrations of oestradiol (EIF), androstenedione (AIF) and inhibin A (IIF) in individual follicles, as markers for follicular health. Oocytes were morphologically evaluated at recovery and thereafter in vitro matured for 24 h in individual wells. Results showed that intrafollicular hormone concentrations were related to follicle size, but surprisingly were higher in smaller follicles. EIF was higher in follicles with 4 mm in diameter in comparison with follicles with 5 and 6 mm, (3.4±1.2 ng/ml vs 1.2±0.3 ng/ml, P<0.01, and 0.8±0.1 ng/ml, P<0.0005, respectively). The ratio EIF:AIF was also higher in 4 mm follicles than in 5 mm follicles (0.2±0.0 vs 0.08±0.0; P<0.0005). IIF concentrations were similar in 4 and 5 mm follicles (13.6±1.6 and 14.0±1.1 μg/ml, respectively) but significantly lower (8.5±0.5 μg/ml, P>0.0005) in 6 mm follicles. No relationship was found between follicle diameter and the ability of oocytes to resume meiosis. Nevertheless, the reduced hormone secretion of the largest follicles, indicates follicular malfunction and could be related to failures in the later embryo development.
01 - 05 Apr 2006
European Society of Endocrinology