Circulating thyrotropin is upregulated by estradiol

Salvatore Benvenga; Flavia Di Bari; Roberta Granese; Irene Borrielli; Grazia Giorgianni; Loredana Grasso; Maria Le Donne; Roberto Vita; Alessandro Antonelli

doi:10.1016/j.jcte.2018.02.002

Circulating thyrotropin is upregulated by estradiol

J Clin Transl Endocrinol. 2018 Feb 13:11:11-17. doi: 10.1016/j.jcte.2018.02.002. eCollection 2018 Mar.

Authors

Affiliations

¹ Department of Clinical and Experimental Medicine, Section of Endocrinology, University of Messina, 98125 Messina, Italy.
² Master Program on Childhood, Adolescent and Women's Endocrine Health, University of Messina, 98125 Messina, Italy.
³ Interdepartmental Program on Molecular & Clinical Endocrinology, and Women's Endocrine Health, University hospital, A.O.U. Policlinico Gaetano Martino, 98125 Messina, Italy.
⁴ Department of Obstetrics and Gynecology, University Hospital G. Martino, 98125 Messina, Italy.
⁵ Service of Immunometry and Laboratory Diagnosis, University Hospital G. Martino, 98125 Messina, Italy.
⁶ Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy.

Abstract

After encountering two women with serum thyrotropin (TSH) levels greater in periovulatory phase than in other days of the menstrual cycle, we hypothesized that TSH levels could be sensitive to changes in circulating estrogens in women. The objective of this study was to evaluate whether serum TSH increases after an induced acute increase of serum estradiol, and compare serum TSH increase with that of prolactin (PRL) which is a classic estradiol-upregulated pituitary hormone. In this retrospective study, we resorted to stored frozen sera from 55 women who had undergone the GnRH agonist (buserelin)-acute stimulation test of ovarian steroidogenesis. This test, that is preceded by dexamethasone administration to suppress adrenal steroidogenesis, had been performed to show an increased buserelin-stimulated response of 17-hydroxyprogesterone, a response that is frequent in polycystic ovary syndrome. Fifty-five women had enough serum volume at pertinent times (first observation early in the follicular phase and all times of the test) to permit assay of serum estradiol, TSH and PRL. Before dexamethasone administration, estradiol averaged 26.4 ± 15.5 pg/ml (reference range 23-139, follicular phase), TSH 1.78 ± 0.86 mU/L (reference range 0.3-4.2) and PRL 409.4 ± 356 mU/L (reference range 70.8-556) (mean ± SD). Serum estradiol, TSH and PRL averaged 47.2 ± 27 pg/ml, 0.77 ± 0.48 mU/L and 246.4 ± 206.8 mU/L just prior to the buserelin injection, but they peaked at 253.4 ± 113.5 pg/ml (nv 83-495, midcycle), 3.30 ± 1.65 mU/L and 540.3 ± 695.2 mU/L after injection. The responses to buserelin of estradiol, TSH and PRL were of wide magnitude. There was a significant correlation between TSH peak and serum estradiol peak, betweeen AUC0-24 h-TSH and AUC0-24 h-estradiol, or between PRL peak and estradiol peak and AUC0-24 h -PRL and AUC0-24 h-estradiol in only a subgroup of women. Therefore, women with estradiol-dependent increase in serum TSH do exist. Reference bands of serum TSH dependent on the phases of the menstrual cycle should be available.

Keywords: 17-OHPg, 17-hydroxyprogesterone; AUC, area under the curve; Buserelin; E2, estradiol; Estradiol; FSH, follicle-stimulating hormone; FT3, free T3; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; Menstrual cycle; PCOS, polycystic ovary syndrome; PRL, prolactin; Polycystic ovary syndrome; Prolactin; T3, triiodothyronine; T4, thyroxine; TRH, TSH-releasing hormone; TSH, thyrotropin; Thyrotropin.