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Bright light exposure and pituitary hormone secretion
I Kostoglou-Athanassiou1, D F Treacher, M J Wheeler
1Department of Gynaecology, St Thomas' Hospital, UMDS, London, UK.
Clinical Endocrinology
|March 24, 1998
Summary
Bright light exposure disrupts the natural melatonin cycle, affecting pituitary hormone secretion including cortisol, growth hormone, and prolactin. Modifying sleep schedules also impacts vasopressin levels.
Area of Science:
- Endocrinology
- Chronobiology
- Neuroscience
Background:
- Melatonin secretion is inhibited by bright light.
- The relationship between melatonin and pituitary hormone function requires further investigation.
Purpose of the Study:
- To investigate the effect of bright light exposure on melatonin rhythm and pituitary hormone secretion.
- To understand how altering the melatonin rhythm impacts cortisol, growth hormone (GH), and prolactin (PRL) secretion.
Main Methods:
- Randomized controlled clinical trial involving ten healthy adult males.
- Exposure to bright light or normal room lighting during early hours of darkness (2000h-0200h).
- Measurement of serum cortisol, GH, PRL, plasma vasopressin, oxytocin, melatonin, and other parameters over 24 hours.
Main Results:
- Bright light delayed the nocturnal melatonin peak by 2 hours, decreasing cortisol levels.
- Growth hormone (GH) levels initially decreased with a subsequent significant nocturnal increase.
- Prolactin (PRL) peak was delayed, and nocturnal vasopressin concentrations were lower with modified sleep schedules.
Conclusions:
- Exposure to bright light during early darkness alters melatonin, cortisol, GH, PRL, and nocturnal vasopressin secretion.
- Sleep pattern modification, independent of light exposure, reduces vasopressin concentrations and alters its nocturnal peak.