Endocrine Abstracts

The suprachiasmatic nucleus (SCN) is the ‘master clock’ of the mammalian brain. It coordinates the peripheral clock in body, including the pineal clock that receives SCN input via a multisynaptic noradrenergic pathway. Melatonin is exclusively involved in signaling the ‘time of day’, ‘time of year’ to all tissues and is thus considered to be the chronological pacemaker or ‘zeitgeber’.

Objective: To determine the chronology of age-related changes in melatonin secretion and relationship with gonadotropin and cortisol levels.

Subjects and methods: Data were combined from a series of studies conducted between 1997 and 2006. A total of 60 healty subjects, aged 3 to 70 years, without sleep complaints or histories of endocrine psychiatric disorders were enrolled. Twenty-four hour profiles of urine aMT6 s, cortisol and gonadotropins were assayed by cosinor analysis.

Results: The circadian patterns of melatonin secretion exhibited a significant decline around pubescence; in younger adults there was no significant change or sex-differences. Correlations between melatonin secretion and gonadotropins showed a positive correlation at the onset of puberty and negative one in both premenopausal women (at ovulation) and men (<60 y). In menopausal women there was a very large variability in chronobiological parameters associated with an increase in gonadotropin excretion, LH and FSH. An age-related decline in melatonin was found after 55–60 years of age. Whereas circadian rhythms persisted, they were associated with earlier timing acrophases and blunted amplitudes. Cortisol secretion exhibited significant circadian rhythm but with a surprisingly long time log; the acrophase occurred across the 24 h.

Conclusion: Aging influences both the amplitude and phase of circadian rhythmicity and melatonin could be an index of circadian rhythm function.

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