Crosstalk between gonadotropins and thyroid axis

Gonadotropins and thyroid hormones are essential, respectively, for reproduction and metabolism. The classical endocrinological approach is based on the detection of axes that start from the hypothalamus and arrive at the final effector organ, in this case gonads and thyroid. However, several clues suggest that these axes do not work in parallel, but they dialogue with each other. In this article, we review evidences demonstrating crosstalk between gonadotropins and thyroid axis. Firstly, there is an undeniable structural similarity of both hormones and receptors, maybe due to a common ancient origin. This structural similarity leads to possible interaction at the receptor level, explaining the influence of thyroid stimulating hormone on gonadal development and viceversa. Indeed, altered levels of thyroid hormones could lead to different disorders of gonadal development and function throughout entire life, especially during puberty and fertile life. We here report the current knowledge on this item both in males and in females. In particular, we deepen the interaction between thyroid and gonads in two situations in females: polycystic ovary syndrome, the most frequent cause of menstrual alteration, and pregnancy.