MELATONIN AND HUMAN PUBERTY - CURRENT PERSPECTIVES

Many studies of melatonin in human puberty are difficult to interpret in light of methodological considerations such as the use of single blood samples collected either during the day or at night; a small number of observations; the failure to include the temporal characteristics of melatonin secretion; the definition of puberty by the use of broad clinical features without use of hormonal markers of puberty; the lack of control for the actual duration and intensity of light exposure during the days preceding the study; and the cross sectional nature of most studies. The few studies that have examined the plasma melatonin rhythm in humans by multiple blood sampling overnight or over 24 hr suggest that normal pubertal development (as well as normal ovarian function) are not linked to alterations in the plasma melatonin profile. There is, however, some evidence to suggest that disorders of the hypothalamic-pituitary-gonadal axis (delayed puberty, precocious puberty, hypothalamic amenorrhea) may be linked to altered plasma melatonin profile, at least in some cases. These findings, taken together with strong evidence for the role of the pineal gland in the reproductive function of other vertebrate species, render unlikely the inference that the pineal gland has no role in the development and function of the human reproductive axis. Thus, one may speculate that a pineal-puberty relation does exist in humans and that the research techniques applied to date have been inadequate to uncover this relation. Greater knowledge might be gained from studies of melatonin metabolism during growth and pubertal maturation, from longitudinal studies of the melatonin rhythm under rigorously controlled conditions of light exposure, and, perhaps, from the development of research strategies to explore the human melatonin receptor in vivo.