Daily Rhythm of Plasma Melatonin in Normal and Precocious Puberty*

A previous study of normal humans has shown a decrease in plasma melatonin at the onset of puberty, suggesting that melatonin may act to restrain pubertal onset. We have measured plasma melatonin throughout a 24-h period in normal and constitutionally short males at different pubertal stages and in patients with idiopathic true precocious puberty and familial male isosexual precocity. The 24-h profile of plasma melatonin was similar for the prepubertal, pubertal, and adult males studied, with all subjects having low levels (20-50 pg/ml) during the day and high levels (80-100 pg/ml) at night between 0100-0500 h. The 24-h profiles of the patients with isosexual precocity were similar to the profiles observed throughout normal puberty. These data do not support a role for melatonin in the initiation of normal or precocious puberty in man.