SERUM LEPTIN LEVELS IN NORMAL-CHILDREN - RELATIONSHIP TO AGE, GENDER,BODY-MASS INDEX, PITUITARY-GONADAL HORMONES, AND PUBERTAL STAGE

It is commonly accepted that at least in girls puberty starts when a m inimum level of body mass or a certain amount of body fat are present. However the precise signal by which adipose stores inform the hypotha lamus of the degree of energetic reserves is unknown. Leptin is a horm one produced by the adipocytes to regulate food intake and energy expe nditure at the hypothalamic level. To understand whether leptin is the adipose tissue signal that allows puberty, 789 normal children of bot h sexes, age 5-15 yr, were transversally studied. Leptin levels, as we ll as gonadal and gonadotropins levels, were analyzed in addition to t he determination of auxological parameters. In an age-related analysis , leptin levels in girls rose from 5-15 yr (from 4.3 +/- 0.4 to 8.5 +/ - 0.9 mu g/L) in parallel with body weight. Boys always had lower lept in levels than girls (3.3 +/- 0.3 mu g/L at 5 yr), but they rose in pa rallel with weight until 10 yr (5.3 +/- 0.7 mu g/L), when a striking d ecrease was observed until 15 yr (3.0 +/- 0.3 mu g/L). In girls, lepti n was the first hormone to rise followed by FSH and later by LH and es tradiol. A similar pattern occurred in boys, despite the fact that lep tin dropped after 10 yr when testosterone rises. Divided into three pu bertal stages, i.e. P1 = prepuberty, P2 = early puberty, and P3 = over t puberty, in girls the four hormones rose progressively from P1 to P3 , but from P2 to P3 the percent increment was greater for LH and estra diol. In boys, leptin decreased from P1 to P3, whereas FSH, LH, and te stosterone rose. The age-related changes were not caused by adiposity variations, because data did not change when subtracting values of chi ldren over 97% of standard deviation score of body mass index. In conc lusion: 1) leptin appears to increase in both boys and girls before th e appearance of other reproductive hormones related to puberty; 2) lep tin levels in boys are always lower than in girls, although they incre ase with age until the age 10 yr; 3) leptin in boys declines about the time testosterone increases. Leptin may well be a permissive factor f or the initiation of pubertal events.