No melatonin suppression by illumination of popliteal fossae or eyelids.

ABSTRACT

A recent report that popliteal illumination shifted the circadian rhythms of body temperature and melatonin challenged the longstanding belief that light phase-shifting the circadian system in mammals is mediated only through the retina. The authors tested effects of popliteal illumination and illumination provided through the eyelids on melatonin suppression. In randomized, counterbalanced orders, healthy volunteers received three treatments from midnight until 200 AM, one on each of three visits to the laboratory. Treatments included (1) no illumination from light pads applied to the popliteal fossae, with light mask maintained at < 3 lux (control); (2) light mask illuminated at 1700 lux, with popliteal light pads extinguished; and (3) popliteal light pads illuminated (13,000 lux) and light mask at < 3 lux (control). Saliva specimens were sampled at midnight, at 100 AM, and at 200 AM. Mean salivary melatonin concentrations rose from an average of 30.8 (3.9) pg/ml at midnight (baseline), to 33.2 (4.0) pg/ml at 100 AM, and to 37.2 (3.8) pg/ml at 200 AM in all three conditions, but no statistical differences were found using repeated-measures ANOVA. No evidence of melatonin suppression by either popliteal or closed eyelid light stimulation was found. These data suggest that bright retinal illumination is necessary for suppression of melatonin mediated through the suprachiasmatic nuclei.