Thyrotropin and thyroid hormones in in vitro follicle growth of mouse primary preantral follicles, in in vitro fertilization and early embryo development

Purpose The aim of the study was to evidence whether Thyrotropin (TSH) and Thyroid hormones (T3 and T4) have an impact in in vitro follicle growth of mouse preantral follicles, in in vitro fertilization and in early embryo development. Methods This prospective observational animal experimental study was conducted on a study population consisted of 100 female and 30 male mice (C57BL/6 x CBA) F1 hybrids, which were allocated in 15 sequential experiments of 5-8 female and 2 male mice each. The experiments were performed through an 8-month period. Preantral follicles were mechanically dissected and cultured in vitro. Mature oocytes were fertilized using sperm from adult male hybrids. The effect of TSH (2 mIU/ml, 1 mIU/ml, 0.2 mIU/ml) and the effect of T3 and T4 (10 M, 10 M, 10 M each), were studied. Early embryo development to the morula/blastocyst stage was assessed. Results Τ3 was found to negatively affect follicular growth and maturation of mouse preantral follicles at the lower 10 -9 M and medium 10 Μ concentrations. Similarly, Τ4 was found to negatively affect follicular growth and maturation at the medium concentration 10 Μ. Contrary to thyroid hormones, no impact of TSH was found in the process of folliculogenesis. Τ3 10 M and 10 M as well as T4 10 M and 10 M had a negative effect on fertilization. In respect to early embryo development, Τ3 10 M was associated with lower 2-cell stage embryo rates. Interestingly, T4 10 Μ resulted in higher 2-cell, 4-cell and morula/blastocyst stage rates. Again, TSH had no effect on fertilization and early embryo development. Conclusions In line with the unfavorable effect of thyroid hormones (T3 and T4) on folliculogenesis and fertilization, a negative impact of T3 was found on the early stages of embryo development. Contrary, T4 promoted specific embryo stages. No effect of TSH on folliculogenesis, fertilization and early embryo development was noted. This study implies a potential latent impact of thyroid hormones in cell functions necessary for fertilization and early embryo