[Neuroendocrinology of puberty. Role of melatonin in man]

A general scheme of the presently known neuroendocrine events occurring with the onset of puberty has been described. Indirect experiments, both in the animal and the human, suggest that the arcuate nucleus located in the medio-basal hypothalamus secretes GnRH by pulses (with increasing amplitude, and probably frequency). GnRH stimulates the secretion of gonadotropins (LH and FSH) with maturation of the ovary and the testis, ripening of the follicle or spermatogenesis and secretion of oestradiol or of testosterone. The theory of the decrease of the sensitivity of the hypothalamus to the sex steroids which was thought to explain the pubertal increase of gonadotropins may not be valid. The increase of the pulsatile secretion of GnRH may be sufficient to explain the pubertal development. However, the response of the gonadotropins is modified by the feed-back mechanism from sex steroids. One of the factor that may influence the pubertal development is the pineal gland. Its main secretory product, melatonin, inhibits the sexual maturation of the rat and of the hamster. Present studies on night and day plasma concentrations and urinary excretions of melatonin do not attribute a role to this indolamine during human pubertal development.