The effects of sex-steroid administration on the pituitary–thyroid axis in transsexuals

Abstract

Objective: Estrogen and androgen administration modulate the pituitary-thyroid axis through alterations in thyroid hormone-binding globulin (TBG) metabolism, but the effects of sex steroids on extrathyroidal thyroxine (T 4 ) to triiodothyronine (T 3 ) conversion in humans are unknown. Design and methods: We studied 36 male-to-female and 14 female-to-male euthyroid transsexuals at baseline and after 4 months of hormonal treatment. Male-to-female transsexuals were treated with cyproterone acetate (CA) 100 mg/day alone (nZ10) or in combination with either oral ethinyl estradiol (or-EE) 100 mg/day (nZ14) or transdermal 17b-estradiol (td-E) 100 mg twice a week (nZ12). Femaleto-male transsexuals were treated with i.m. testosterone 250 mg twice a week. A t-test was used to test for differences within groups and ANOVAwith post hoc analysis to test for differences between the groups. Results: Or-EE increased TBG (100G12%, P!0.001) and testosterone decreased TBG (K14G4%, PZ0.01), but free T 4 did not change. Td-E and CA did not affect TBG concentrations. TSH was not different between groups at baseline or after treatment. CA decreased T 3 /T 4 ratios (K9G3%, PZ0

The evolution of thyroid function with puberty

“…The role of gonadal steroids in this conversion is not clear. A recent study in transsexuals showed that testosterone increased conversion of T4 to T3, while oestrogen (used with cyproterone acetate) did not have any effect on the T3/T4 ratio 21 . Growth hormone rises markedly in puberty and could play a role in this conversion because of its activation of deiodinase type 1 and type 2.…”

“…A recent study in transsexuals showed that testosterone increased conversion of T4 to T3, while oestrogen (used with cyproterone acetate) did not have any effect on the T3/T4 ratio. 21 Growth hormone rises markedly in puberty and could play a role in this conversion because of its activation of deiodinase type 1 and type 2. The lack of a consistent change in TSH probably argues against any significant change in the hypothalamic-pituitary-thyroid axis.…”

Metabolic blood profile of beef heifers during oestrous and non‐oestrous states

“…Fat mobilization, as indicated by increased BHBA during oestrus in dairy cows, was also accompanied by greater T3 concentrations (Mohebbi‐Fani et al., ). Furthermore, the administration of estradiol has been shown to increase the concentration of T3 in women (Bisschop et al., ), which supports the increase in T3 during oestrus. Strong ties between T3 and intermediary metabolism support the key relevance of T3 as a predictor of oestrus.…”

A Unique Presentation Of Thyroid Storm And Myopericarditis In A Young Muscular Man

“…We believe that his supplements contained T4, thus explaining why both T3 and T4 levels were elevated. His testosterone use may have also contributed to his thyrotoxicosis given its role in reduction of thyroid-binding globulin, potentially increasing his unbound thyroid hormone levels (8).…”