Daily and seasonal variations in the concentration of melatonin in the human pineal gland

To elucidate whether pineal melatonin secretion is affected by changes in d ay length, we determined the concentration of melatonin in human pineal gla nds obtained at autopsy from 66 male subjects, aged 16-84 years over a peri od of 12 consecutive months. Based on the time of death, a day-night differ ence in pineal melatonin levels was evident only in the long photoperiod (A pril-September) with significantly higher melatonin concentrations occurrin g at night (2200-1000 h). Nighttime values in the long photoperiod were sig nificantly higher than the nighttime values during the short photoperiod (O ctober-March). During the short photoperiod, the data suggested a possible phase-delay in melatonin secretion. Day-night difference was evident in you ng subjects (30-60 years), but not in elderly subjects (61-84 years). Elder ly subjects had lower total melatonin levels (day and night values) althoug h statistically not significant. Therefore, melatonin levels did not declin e with age and when the data were analyzed by age there was no significant day-night difference in melatonin levels. These data indicate that the conc entration of melatonin in the human pineal is augmented only during the lon g photoperiod. The results suggest a partial effect of photoperiod on melat onin secretion in humans. This may result from living in an artificial ligh t environment or due to other nonphotic signals involved in generating mela tonin rhythm. (C) 1998 Elsevier Science Inc.