Spontaneous diurnal thyrotropin secretion is enhanced in proportion to circulating leptin in obese premenopausal women

Abstract

Context: Recent evidence implicates leptin as an important modulator of thyroid axis activity.

Objective: The objective of this study was to study spontaneous 24-h TSH secretion and 24-h circulating leptin concentrations in obese and lean women.

Design: This was a prospective parallel study (2004).

Setting: This study was conducted at the Clinical Research Center (Leiden University Medical Center, Leiden, The Netherlands).

Participants: Twelve healthy obese premenopausal women (body mass index, 33.2 +/- 0.9 kg/m2) and 11 lean controls (body mass index, 21.4 +/- 0.5 kg/m2) were studied in the follicular phase of their menstrual cycle.

Intervention(s): There were no interventions in this study.

Main outcome measure(s): Spontaneous 24-h TSH concentrations (10-min time intervals) and secretion were calculated using waveform-independent deconvolution technique (pulse). Twenty-four-hour circulating leptin concentrations (20-min time intervals) were measured.

Results: Mean TSH concentration (obese, 1.9 +/- 0.2 vs. lean, 1.1 +/- 0.1 mU/liter; P = 0.009) and secretion rate (obese, 43.4 +/- 5.5 vs. lean, 26.1 +/- 2.2 mU/liter distribution volume.24 h; P = 0.011) were substantially enhanced in obesity, whereas the fasting free T4 (fT4) concentrations were similar (fT4 in obese, 15.4 +/- 1.5 vs. in lean, 16.4 +/- 1.5 pmol/liter; P = 0.147). TSH secretion was positively related to 24-h leptin concentrations (r2= 0.31; P = 0.007).

Conclusions: TSH release is enhanced in the face of normal plasma fT4 concentrations in obese premenopausal women, and hyperleptinemia may well be involved in this neuroendocrine alteration.