Leptin, the product of the ob gene, is a recently discovered hormone secreted by adipocytes. Serum leptin concentrations increase in correlation with the percentage of body fat, but besides that little is known about the physiological actions of leptin in humans. In order to understand the role of leptin in severe malnutrition, in the present work 10 patients recently diagnosed with anorexia nervosa were studied both before and 2 months later, after partial weight recovery, and were compared with 18 normal-weight women as controls. Leptin was measured by a newly developed radioimmunoassay and both IGF-I and IGFBP-3 were measured by commercial radioimmunoassays. The mean (±SE) serum leptin concentrations (in μg/liter) were 18.1 ± 2.0 in control women with BMI of 21.1 ± 0.3, significantly higher (P < 0.01) than that in the anorexia nervosa patients at diagnosis (2.2 ± 0.1, BMI 15.3 ± 0.6). These differences were also observed in IGF-I values (μg/liter) that were 228.0 ± 14.6 in controls and 157.4 ± 28.7 in anorexia nervosa patients (P < 0.02). No differences were observed in IGF-BP3. After treatment, patients with anorexia nervosa experienced an increase in BMI (17.1 ± 0.5, P < 0.0001 vs before) although they were still underweight. The partial recovery in weight led to a complete normalization of IGF-I levels (214.0 ± 21.0 μg/liter) and to an enhancement in leptin levels (3.3 ± 0.5 μg/liter; P < 0.03 vs before treatment), though still lower than those in normal- weight women (P < 0.05). Individually analyzed, a large dispersion was observed in control subjects, with leptin levels ranging from 5.5 to 38.7 μg/liter, while in all anorexia nervosa patients leptin levels were under 3 μg/liter. A treatment-induced increase in body weight led to an increase.
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