Thyroid and sympathetic influences on plasma leptin in hypothyroidism and hyperthyroidism

Objectives: To determine the dependence of plasma leptin concentrations upo n circulating noradrenaline (NA) and thyroid hormones (TH) in humans. Design: Cross-sectional study in 40 newly diagnosed untreated patients with primary thyroid disease, and 69 lean and obese euthyroid control subjects, Measurements: Plasma leptin, NA, free T3 (fT3) and TSH in the fasting state . Anthropometry and % body fat (electrical bioimpedance). Results: Leptin levels were highest in 37 obese euthyroid and 22 hypothyroi d (median [interquartiles]31.5 [19.0 - 48.0], 19.2 [11.5 - 31.5] ng ml(-1)) , and lowest in 32 lean euthyroid and 18 hyperthyroid subjects (6.6 [3.9 - 14.4], 8.9 [5.5 - 11.1]; ANOVA, P < 0.0001). Plasma NA was similar in all g roups (P = n.s,), In obese controls, TSH correlated with % body fat and lep tin (r = 0.67, r = 0.61; P < 0.001). Treatment of hypothyroidism (n = 10) w ith T4 reduced leptin from 20.8 [11.8 - 31.6] to 12.9 [4.6 - 21.2] (P = 0.0 05) with no change in BMI. Conclusions: Thyroid status modifies leptin secretion independently of adip osity and NA. The data suggest leptin-thyroid interactions at hypothalamic and adipocyte level.