Suppression of human melatonin by light over the course of the rising phase of the synthesis
- 1 February 1994
- journal article
- research article
- Published by Taylor & Francis in Biological Rhythm Research
- Vol. 25 (1) , 37-50
- https://doi.org/10.1080/09291019409360273
Abstract
In several animal species the response of the pineal melatonin synthesis to light alters during the night, but the possible changes in humans are not exactly known. Nine volunteers were exposed to 500‐lx light for one hour at different times over the course of the rising phase of the melatonin synthesis. The exposure times were related to the individual circadian phases by using the time point of the half‐maximal melatonin level as a reference. Melatonin was measured by radioimmunoassay in salivary samples collected at 15–120‐min intervals. Only when the melatonin levels were related to the prelight levels, the light‐induced suppression was smaller and the postlight recovery was greater in the early than in the late rising phase. No differences were found, if the levels were related to the corresponding control values. Thus, the sensitivity of the human melatonin synthesis to light did not change during the rising phase. It cannot explain the increase of the light‐induced phase delays of circadian rhythms that is supposed to occur during the first half of the night.Keywords
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