Leptin reduces body weight gain in neonatal rats

Leptin (OB protein) elicits a neuroendocrine response to starvation and sta tes of nutritional abundance to stabilize the proportion of body fat. Lepti n has dramatic effects an food intake and energy expenditure in adult and j uvenile rodents. However, whether the neonatal period is associated with th e development of an effective leptin feedback system is still not known. In this study, we evaluated the effects of peripherally administered leptin o n body weight changes in neonatal rats during the early suckling period (fr om birth to 10 d). Our results show that daily i.p, injections of leptin (0 .3 mu g/g and 1.0 mu g/g) to neonatal rats led to a significant reduction i n weight gain over 10 d compared with the control group (p < 0.01 and p < 0 .01, respectively). Concomitant with a reduction in weight gain, retroperit oneal fat pod weight also significantly decreased in the leptin-treated gro up. Our data indicate that the potential for energy balance regulation by l eptin occurs in the first day after birth. In addition, we also observed th at 3 d after discontinuing leptin treatment, the body weight as well as the fat pad weight of leptin-treated pups returned to the control level. Our r esults demonstrate that leptin reduces body weight gain in neonatal rats.