Serum melatonin in central precocious puberty is lower than in age-matched prepubertal children

In children a progressive decrease in nocturnal serum melatonin (MT) has been shown with advancing age, suggesting a reduction in the amplitude of the circadian MT curve with maturation. Whether this alteration of MT levels is related to human sexual maturation or occurs independently remains to be elucidated. Also, the impact of gonadal steroids on the MT rhythm remains an open question. We examined 56 patients (51 females and 5 males) with central precocious puberty (52 idiopathic and 4 neurogenic). Patients were studied before and 3, 6, and 12 months after initiation of GnRH analog treatment. Three hundred and thirty-seven endocrinologically normal subjects (190 males and 147 females) served as controls. In all subjects nocturnal serum MT (blood collection between 2300 and 0100 h) was measured with a highly specific RIA. In young patients, aged 1-5 yr, we found significantly lower MT levels than in age-matched controls. Pubertal patients, aged 5-9 yr, displayed nocturnal MT levels in the same range as control subjects approaching normal pubertal age. In contrast to endocrinologically normal children, there was no age-dependent decrease in nocturnal MT in untreated precocious puberty; rather, it appeared that serum MT had already declined in association with the onset of sexual maturation. Although there was a significant difference in weight between patients and age-matched controls, the low MT values in patients 1-5 yr old were only partly explained by the weight difference (P less than 0.0009); their pubertal status also contributed significantly (P less than 0.006). Pituitary-gonadal suppression induced by long term GnRH analog treatment did not result in a return to prepubertal MT levels; rather, nocturnal MT decreased during therapy. The collected data indicate that nocturnal serum MT levels are related to sexual maturation, since serum MT is similar in precocious puberty and normal pubertal children. Since suppression of the pituitary-gonadal axis did not result in increases in nocturnal MT levels in young patients with precocity (i.e. return to age-appropriate levels), the reduction of nocturnal MT with normal puberty is not likely to be dependent on pubertal gonadotropin or sex steroid milieu.