Ricerc@Sapienza

The thyroid hormones (THs) triiodothyronine (T3) and tetraiodothyronine,
or thyroxine (T4), not only dramatically impact on
development and differentiation, but also on the sexual and
reproductive function. There is large body of literature, in fact, on
the effects of THs on the reproductive function in both humans
(Poppe and Velkeniers, 2004; Wajner et al., 2009) and animals
(Hapon et al., 2010; Nelson et al., 2011).
For a long time the gonads were thought to be unresponsive to
THs, but TH receptors (TR) were discovered in rat (Jannini et al.,
1990; Palmero et al., 1988) and then in human testis (Jannini
et al., 2000). In women, the association of menstrual disturbance
with thyroid disease was described as early as 1840 by von Basedow,
but the discovery of TRs in the ovary was carried out at the
end of last century (Wakim et al., 1994b). Therefore, the link between
thyroid and reproductive function was well established.
Since then, research has shown that thyroid dysfunction is associated
with an adverse effect on fertility, both in men (Wagner et al.,
2009) and women (Dittrich et al., 2011). There is also evidence that
THs can affect the sex steroid hormone axis (Bagamasbad and
Denver, 2011), consequently sexual hormones and the pituitary
gland can mediate the action of THs on the reproductive
physiology.
While the effects of THs on fertility have been widely studied,
little is known about their influence on sexual function. In the last
few years, an increasing number of evidences have shown the influence
of THs on male sexual function, particularly on ejaculation
control as well on desire and erectile function (Carani et al., 2005;
Corona et al., 2012b; Di Sante et al., 2016). The female sexual
function and the relationship with thyroid function is still less
studied. Furthermore, studies conducted on animals have shown
the presence of TRs in the male (Carosa et al., 2010) and female
genitalia (Rodriguez-Castelan et al., 2017). Moreover, knockout
mice for TRs showed alterations in sexual behavior (Dellovade et al.,
2000).
The purpose of this review is to summarize and discuss the
available data on the influence of THs on male and female sexual
function to understand the molecular mechanisms of the influence
of the thyroid gland on sexual behavior and function.