Abstract
According to the current view, the main function of the pineal gland and its hormone melatonin is to convey information on environmental photoperiods to the endocrine, central nervous and immune systems, allowing their optimal adjustment to the time of the day and season. Within the endocrine system, the gonads are a major target; maturation of the female reproductive organs during pubertal development is inhibited by the pineal hormone. During the reproductive phase, melatonin seems to act as a coordinating signal for the menstrual cycle by timing the LH-peak and supporting progesterone production. A gradual decline of circulating melatonin with age suggests a role in age-associated endocrine changes, e.g. during menopause. Due to its important role in the female reproductive system, the pineal gland has been implicated in the aetiology of human breast cancer. Serum melatonin is depressed in patients with primary mammary cancer and experimental tumours are inhibited, a finding suggesting a therapeutic potential of melatonin. In addition, other potent antineoplastic substances exist in the pineal gland, which may become useful tools for future anti-cancer therapies.