Plasma melatonin levels and nocturnal transitions between sleep and wakefulness.

During night (11 p.m.-7a.m.) blood was sampled in darkness via an indwelling intravenous catheter simultaneously with polygraphic sleep registration in 7 normal men. The nocturnal melatonin secretion patterns exhibited secretory episodes. Spontaneous waking episodes were shown to be significantly correlated to the occurrence of melatonin peaks (chi c2 = 9.0, p less than 0.005 Melatonin nadirs were significantly associated with rapid eye movement periods (chi c2 = 12.8, P less than 0.005) but not with other sheep stages evaluated by standard criteria. It is hypothesized that melatonin secreted in connection with arousals during night may in turn act to restore sleep in humans.