The plasma prolactin levels in man during prolongation of darkness in the morning.
The plasma prolactin levels were studied in 4 healthy subjects with a constant sleep-waking cycle and a constant activity schedule before and after experimental alteration of the dark-light cycle.  The subjects slept in the dark from 10.30 p.m. to 6.30 a.m.  During a control period of 10 days the subjects stayed in rooms which were well lighted after 6.30 a.m.  During the following 10 days darkness was prolonged by 4 hours until 10.30 a.m. Blood samples were obtained at 10.30 p.m., and each hour from 2.30 to 11.30 a.m. on days 9 and 10 of each period of investigation.  In all the subjects an increase of the plasma prolactin level occurred during sleep.  At about the time of waking the concentration fell rapidly.  There was no apparent shift in the waking-related decrease in the prolactin level during the experimental period with extended darkness.  Present data do not indicate that the dark-light transition in the morning is essential for the waking-related decrease in the prolactin level.
D000328:Adult; D001143:Arousal; D002940:Circadian Rhythm; D003624:Darkness; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011388:Prolactin / Q000097:blood*
D011388:Prolactin