ABSTRACT
AIM: This study was designed to investigate the longitudinal and dynamic profile of leptin and its relationship with sex hormones including luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol (E2) and testosterone (TTE) in neonatal 'minipuberty'. We also investigated the effects of leptin in the regulation of body weight gain and body mass index (BMI) in the first 3 months of life. METHODS: A longitudinal study was carried out in a cohort of 15 male and 15 female term infants during the first 3 months of life. Blood samples were collected in the morning from the infants on the 3rd, 15th, 30th, and 90th days of life. At each sample collection, anthropometric measurements were recorded. Serum leptin, LH, FSH, E2 (girls only) and TTE (boys only) concentrations were analyzed using standard biochemical methods. Association of leptin with weight gain, BMI, and these hormones during infancy was evaluated. RESULTS: Leptin levels increased significantly between the 3rd and 90th days of life in both boys and girls. BMI of both groups increased significantly from the 3rd to the 90th day. There was no significant difference in the leptin levels and leptin/BMI ratios of the two sexes at different time points. Leptin levels on the 30th and 90th days correlated significantly with BMI in both sexes. LH and FSH levels in both groups were found to be significantly higher on the 15th day of life. No correlation was observed between leptin and LH, FSH, E2 or TTE levels throughout the study. CONCLUSIONS: Leptin levels do not differ between the two sexes during early infancy and possibly there is no role for leptin in the surge of gonadotropins or sex steroids in neonatal minipuberty. The relationship between leptin and BMI could not be seen in the first postnatal days and the transient lack of the regulatory effect of BMI on leptin concentrations might reflect an adaptive resistance in the production of leptin to support catch-up growth after initial physiological weight loss in newborns.
