Endocrine Abstracts

Objective: The present study examined the influence of light and dark, seasonal differences, electromagnetic fields, adrenergic and GABA-ergic control, age on melatonin secretion and also which factors affect rhythmicity of melatonin secretion, both in health and disease.

Data were combined from a series of studies conducted between 1997 and 2006. Hormones were temporally assayed by immunometric assays.

The results showed that melatonin is secreted in a circadian pattern with high levels during the night and low ones in the day time and constant from day to day in the same subject when the individual behavior and environment remain relatively unchanged but there is very large variability in amplitude among subjects. In a structured environment there are changes in melatonin production in seasonal photoperiod. In short photoperiod seasons the melatonin circadian profile amplitude is the highest while in long photoperiod seasons it is diminished. Occupational exposure to extremely low frequency magnetic fields altered profiles of melatonin secretion in electric power station workers.

Inhibition of the beta-adrenergic receptor by beta-blockers accounts for approximately 80% of the nightly increase in melatonin production. Benzodiazepine receptors have been found to modulate melatonin production.

The amplitude of circadian rhythm of melatonin decreases with age. Changes in melatonin secretion in puberty development and menstrual cycle and also in disorders of hypothalamic-pituitary-gonadal axis suggest that melatonin by its circadian secretion regulates the temporal organization of HPG axis. Results related to epileptic disorders in children showed disturbances of melatonin circadian rhythm.

Conclusion: The results showed that melatonin is a chronobiotic hormone regulated by light with the ability to modulate various bodily functions using hormones and restore the balance when disorders of circadian regulation occur.

Acknowledgements: The study was done under research project CEEX 100/2006.