The effects of sex-steroid administration on the pituitary-thyroid axis in transsexuals.
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 (T4) to triiodothyronine (T3) conversion in humans are unknown.


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 (n = 10) or in combination with either oral ethinyl estradiol (or-EE) 100 microg/day (n = 14) or transdermal 17beta-estradiol (td-E) 100 microg twice a week (n = 12). Female-to-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 ANOVA with post hoc analysis to test for differences between the groups.


RESULTS
Or-EE increased TBG (100 +/- 12%, P < .001) and testosterone decreased TBG (-14 +/- 4%, P = 0.01), but free T4 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 T3/T4 ratios (-9 +/- 3%, P = 0.04), suggesting that T4 to T3 conversion was lower. Testosterone increased T3/T4 ratios (30 +/- 9%, P = 0.02), which probably reflects higher T4 to T3 conversion.


CONCLUSIONS
Oral but not transdermal estradiol increases TBG, whereas testosterone lowers TBG. Testosterone increases T3/T4 ratios. Estradiol does not affect T3/T4 ratios, irrespective of the route of administration.
Bisschop
Peter H
PH
Department of Endocrinology and Metabolism, Laboratory of Endocrinology, Academic Medical, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands. p.h.bisschop@amc.uva.nl
Toorians
Arno W
AW
Endert
Erik
E
Wiersinga
Wilmar M
WM
Gooren
Louis J
LJ
Fliers
Eric
E
D000328:Adult; D000726:Androgen Antagonists / Q000494:pharmacology; D000728:Androgens / Q000494:pharmacology; D003534:Cyproterone / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000494:pharmacology*; D006801:Humans; D007453:Iodide Peroxidase / Q000378:metabolism; D008297:Male; D010053:Ovary / Q000502:physiology; D010902:Pituitary Gland / Q000187:drug effects*; D013737:Testis / Q000502:physiology; D013961:Thyroid Gland / Q000187:drug effects*; D013974:Thyroxine / Q000097:blood; D014189:Transsexualism / Q000378:metabolism*; D014284:Triiodothyronine / Q000097:blood
D000726:Androgen Antagonists; D000728:Androgens; D004967:Estrogens; D012739:Gonadal Steroid Hormones; D014284:Triiodothyronine; D003534:Cyproterone; D007453:Iodide Peroxidase; D013974:Thyroxine