OBJECTIVES: To determine the dependence of plasma leptin concentrations upon 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 hypothyroid (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 groups (P= n.s.). In obese controls, TSH correlated with % body fat and leptin (r= 0.67, r= 0.61; P< 0.001). Treatment of hypothyroidism (n= 10) with T4 reduced leptin from 20.8 [11.8-31.6] to 12.9[4.6-21.2] (P= 0.005) with no change in BMI. CONCLUSIONS: Thyroid status modifies leptin secretion independently of adiposity and NA. The data suggest leptin-thyroid interactions at hypothalamic and adipocyte level.
OBJECTIVES: To determine the dependence of plasma leptin concentrations upon 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 hypothyroid (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 groups (P= n.s.). In obese controls, TSH correlated with % body fat and leptin (r= 0.67, r= 0.61; P< 0.001). Treatment of hypothyroidism (n= 10) with T4 reduced leptin from 20.8 [11.8-31.6] to 12.9[4.6-21.2] (P= 0.005) with no change in BMI. CONCLUSIONS: Thyroid status modifies leptin secretion independently of adiposity and NA. The data suggest leptin-thyroid interactions at hypothalamic and adipocyte level.