Thyroid hormone regulation of mammalian reproductive development and the potential impact of endocrine-disrupting chemicals

Thyroid hormones are essential for growth and development of all vertebrate organisms. A growing literature reveals that thyroid hormones are centrally important in the development of reproductive tissues. In males, the predominant target is the developing testis with aberrant Sertoli and Leydig cell development and accompanying testicular dysfunction. Hypothyroidism has also been associated with precocious puberty in a distinct subpopulation of adolescent girls. The hypothalamic-pituitary-thyroid axis is the target of numerous endocrine-disrupting chemicals. Intriguingly, many of these chemicals also perturb the development and function of mammalian reproductive tissues. We now review the key literature detailing the role of thyroid hormones in mammalian reproductive development and provide an analysis of the evidence linking thyroidal disruption by polychlorinated biphenyl, polybrominated diphenyl ether, phthalate, triclosan, and bisphenol A exposure, with maldevelopment of mammalian reproductive systems.