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

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/m(2)) and 11 lean controls ( body mass index, 21.4 +/- 0.5 kg/m(2)) 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 T-4 (fT(4)) concentrations were similar (fT(4) 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 (r(2) = 0.31; P = 0.007). Conclusions: TSH release is enhanced in the face of normal plasma fT(4) concentrations in obese premenopausal women, and hyperleptinemia may well be involved in this neuroendocrine alteration.