THYROTROPIN SECRETION IN HEALTHY SUBJECTS IS ROBUST AND INDEPENDENT OF AGE AND GENDER, AND ONLY WEAKLY DEPENDENT ON BODY MASS INDEX

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 414-431-HPT Axis Biology
Clinical
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-416
Ferdinand Roelfsema*1, Petra Kok2, Hanno Pijl3, Nienke R Biermasz1, Alberto M. Pereira4 and Johannes D Veldhuis5
1Leiden University Medical Center, Leiden, Netherlands, 2Leiden University Medical Center, Leiden, Netherlands, 3Leiden University Medical Center, Leiden, Netherlands, 4Leiden University Medical Center, The Netherlands, 5Mayo Clinic, Rochester, MN
Background: Studies on the influence of sex, age  and body weight  on TSH secretion are not unanimously. The majority of these investigations  are based on a single TSH measurement. Reports on TSH secretion,  using 24-h blood sampling generally compared young vs. old subjects, lean vs. obese subjects or  men vs. women. The value of these studies is restricted because TSH secretion was not studied across the whole data range of age and body weight (BMI),  thereby potentially  introducing statistical limitations (1-3).

Aim: To report TSH secretion data of a large number (n=117) healthy subjects , who underwent 10-min blood sampling during 24-h.

Methods: TSH was measured by a sensitive IFMA (Wallac Oy, Turku, Finland), and calibrated against WHO IRP 80/558. Secretion parameters were calculated with an automatic Matlab-based deconvolution program (4).

Results: The age range was 22-77 yr, BMI 18-39 kg/m2, FT4 9.4-23.1 pmol/l, number of pulses 18.4 ± 4.3 /24-h (mean ± SD), basal secretion 20.7 ± 11.4 mU/l, pulsatile secretion 19.4 ± 12.2 mU/l and total secretion 40.1 ± 21.1 mU/l. There were no sex differences in pulse frequency, hormone half-lives, secretion modes, basal, pulsatile and total secretion or pulse regularity. Basal and total TSH secretion were linearly dependent on BMI with higher basal and total TSH secretion with higher BMI (β basal 0.63 ± 0.20, P=0.003, β total secretion 0.807 ±0.39, P=0.039). Age and gender were not significant factors in the full regression model. Body mass index did not correlate with other secretion parameters, including pulse frequency, half-lives, secretion mode (time needed for reaching the maximal secretion rate within a pulse), mean pulse mass and pulse regularity. Free T4 levels did not correlate with any of the TSH deconvolution parameters, including pulse frequency hormone half-lives , basal or total secretion, BMI and age.

Conclusion:  TSH secretion appears to be robust across sex and age, and only weakly dependent on BMI.  This result contrasts sharply with secretion parameters derived from deconvolution of 24-h  plasma profiles of GH, ACTH and prolactin in comparable healthy controls series, which all are dependent on BMI, age and gender, albeit in different ways.

1.  Barreca et al. JCEM 76:983-87, 1993 2. Greenspan et al. AJP 260:E486-E491, 1991 3. Kok et al. JCEM 90:6185-6191, 2005 4. Keenan et al. AJP 285:R664-R673, 2003

Nothing to Disclose: FR, PK, HP, NRB, AMP, JDV

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm