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Thyrotropin Secretion Profiles Are Not Different in Men and Women

Department of Endocrinology and Metabolic Diseases (F.R., A.M.P., J.A.R.), Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; Department of Endocrinology and Metabolism (R.A., E.E., E.F.), Academic Medical Center of the University of Amsterdam, 1100 DE, Amsterdam, The Netherlands; and Endocrine Research Unit (J.D.V.), Mayo Medical and Graduate Schools, Clinical Translational Research Center, Mayo Clinic, Rochester, Minnesota, 55901

Address all correspondence and requests for reprints to: Ferdinand Roelfsema, Leiden University Medical Center, Department of Endocrinology and Metabolic Diseases, P.O. Box 9600, 2300 RC Leiden, The Netherlands. E-mail: f.roelfsema{at}lumc.nl.

Context: The hypothalamo-pituitary-thyroid axis in women may differ from that in men. Previous reports have shown an almost 2-fold increased response to TRH in females compared with males.

Objective: We analyzed TSH profiles in healthy men and women to delineate differences in the hypothalamo-pituitary-thyroid system.

Subjects and Intervention: The subjects, 24 men (mean age 44 ± 3 yr) and 22 women (mean age 42 ± 3 yr) underwent a 24-h study with blood sampling intervals of 10 min. Premenopausal women were investigated in the early follicular phase of the cycle.

Methods: Serum TSH concentration profiles were analyzed with a newly developed automated deconvolution program, approximate entropy, and cosinor regression.

Results: Basal and pulsatile TSH secretion, and also pulse frequency, hormone half-lives, and secretory mode were indistinguishable in the two genders. There were no differences in diurnal variation, and the times of maximal secretion coincided. Approximate entropy, reflecting secretory regularity, was not different between men and women. In women but not men, TSH secretion was dependent linearly on age.

Conclusions: TSH secretion is gender invariant and depends on age in women only.