Urinary melatonin: a noninvasive method to follow human pineal function as studied in three experimental conditions

Area of Science:

• Endocrinology
• Chronobiology
• Biochemical analysis

Background:

• Melatonin secretion exhibits diurnal and seasonal patterns, crucial for regulating circadian rhythms.
• Urinary 6-sulfatoxymelatonin (aMT6s) is a commonly used marker for melatonin production.
• The utility of urinary melatonin as an alternative marker requires further investigation.

Purpose of the Study:

• To evaluate urinary melatonin as an indicator of melatonin secretion compared to urinary aMT6s.
• To assess the diurnal and seasonal variability of urinary melatonin and aMT6s.
• To determine the correlation between urinary markers and serum melatonin levels.

Main Methods:

• 15 subjects completed three 24-hour periods in a climatic chamber during winter and summer.
• Blood and urine samples were collected at 2- to 5-hour intervals.
• Serum melatonin, urinary melatonin, and urinary aMT6s were quantified using radioimmunoassay.

Main Results:

• Serum melatonin showed a 10-fold increase from day to night.
• Urinary melatonin increased 1.7-fold nocturnally, while urinary aMT6s increased 4.6-fold.
• Both urinary melatonin and aMT6s correlated significantly with serum melatonin levels across all periods.

Conclusions:

• Both urinary melatonin and aMT6s are effective indicators of melatonin secretion.
• Urinary melatonin exhibits less variation than aMT6s, suggesting it may be a more sensitive marker for diurnal and seasonal changes.
• The diurnal variation in the urinary melatonin/aMT6s ratio may indicate changes in liver metabolism of melatonin.