Grant: China-Canada Joint Health Research Initiative

Thyroid hormone [TH (T3 and T4)] is important for normal reproduction function and dysregulation of TH support is associated with reproductive disorders, including impaired follicular development. The hypo- and hyper-thyroidism are associated with dysregulation of the hypothalamic-pituitary axis and suppressed ovarian follicular growth and function. The destiny of the ovarian follicle (growth/ovulation and atresia) is dependent on a delicate balance in the expression and actions of factors promoting follicular cell proliferation, differentiation and apoptosis. While follicle development is markedly hampered in hypothyroidism, this ovarian condition can be markedly improved by TH, especially in the presence of FSH. FSH and T3 interact in promoting preantral follicular growth and this regulation is mediated through GDF-9-dependent FSH receptor mRNA expression. However, the nature of this TH--FSH--GDF-9 interaction is poorly understood. Also, although TH nuclear receptors are expressed in the follicle and mediates the growth promoting action of TH, mechanism of action of TH in regulating follicle development is not known.