Phase‐shifting effects of light on the circadian rhythms of 5‐methoxytryptophol and melatonin in the chick pineal gland

Rhythmic concentrations of 5-methoxytryptophol and melatonin in the chick pineal gland fluctuate in opposite phases.

• The concentrations of 5-methoxytryptophol and melatonin exhibit circadian rhythms that persist in constant darkness.
• Acute exposure to white light at night increases pineal 5-methoxytryptophol and decreases melatonin levels.
• A 6-hour light pulse applied early in the subjective night delays the rhythms of 5-methoxytryptophol and melatonin by 3.7 and 4.5 hours, respectively.
• When light is applied during the late subjective night, it advances the rhythms of 5-methoxytryptophol and melatonin by 8.1 and 11.9 hours, respectively.
• The effects of light on the phase of circadian rhythms are more pronounced for 5-methoxytryptophol compared to melatonin.

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