Serum Leptin Concentrations and Body Fat in Healthy Premature and Term Infants. • 1373

Intro: Leptin is expressed only by fat tissue thus reflecting body energy stores. A gene defect causing heavy obesity was identified in mice. In adult humans, leptin levels are highly correlated with the amount of body fat and decrease after weight loss. Purpose: To study leptin expression in healthy preterm (PN) and term neonates (TN) as a function of body fat. Methods: Prospective study, ethical committee approval, written informed parental consent. 46 infants:PN: n=30, GA (median, IQR) 32 wks (30-32), birth weight 1500 g(1130-1710); TN: n=16, 40 wks (37.6-40.5), 3880 g (3020-4240). Measurement of leptin in routinely obtained serum samples and of body composition using DXA (QDR-1500W, pediatric vers. 5.67, Hologic, Waltham) and a leptin RIA (100 μl serum, rabbit antibody against rh-leptin, radioiodinated leptin tracer^[1]). Age at study:PN: 14 d (9-17); TN: 4 d (3-7). All infants were fed orally (breast milk and/or formula). Results: Median (IQR) body weight, body mass index (BMI) [g/cm²] and% fat mass: PN: 1640 g(1395-2025), 0.96 g/cm² (0.85-1.04), 6.3% (4.7-8.2); TN 3740 g(2940-4000); 1.40 g/cm² (1.25-1.48); 13.2% (9.7-19.7). Leptin levels of neonates (PN: 0.131 μg/L (0.059-0.230); TN: 0.511 (0.247-0.844)) are lower than those found in pediatric or adult subjects with comparable%body fat (range of leptin median 0.5-5 μg/L^[1]). Leptin levels are closely related to neonatal BMI: leptin [μg/L] = 0.004 exp(3.581 BMI); r² = 0.911. Tab. 1 shows leptin levels vs%body fat. Conclusion: The concentration of leptin in neonates is also related to% body fat suggesting that this feedback mechanism may already operate in the neonatal period.

Table 1