Effects of “Jet Lag ” on Hormonal Patterns. II. Adaptation of Melatonin Circadian Periodicity*

Abstract

The plasma melatonin concentration was measured by RIA in samples obtained at 15-min intervals during seven 24-h studies staggered over a period of 10 weeks (October to January). The five normal male volunteers underwent a 7-h westward time shift by jet preceding the second study and, 1 month later, a 7-h eastward shift preceding the fifth study. In the basal, unperturbed state, the 24-h plasma melatonin profile was characterized by a nocturnal elevation, approximately 2.5-fold above the mean daytime value, occurring at 0130 ± 0039 local time, thus 2.5 h after exposure to darkness and 1.5 h after sleep onset. Episodic fluctuations occurred throughout the entire 24-h period. A significant decrease in the 24-h sleep and daytime mean melatonin levels was observed only after the westward trip, during which the difference between sunrise and sunset (daylight duration) was 16 h rather than 10 h. Shifts in the acrophase observed on the day after the westward trip indicated partial adaptation (>2-and <5-h shift),...