Light Synchronization of the Circadian Rhythm of Plasma 11-Hydroxycorticosteroids in Man

Abstract

The levels of plasma 11-hydroxycorticosteroids 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 h until 10.30 a. m. Hourly blood samples were obtained from 2.30 to 11.30 a.m. on days 9 and 10 of each period. Following the period of prolonged darkness there was a shift in the rhythm of the plasma 11\ x=r eq-\ hydroxycorticosteroids. The secretion period in the morning started later than during the control period. Present data indicate that in man the dark-light transition is important for the synchronization of the circadian plasma cortisol rhythm in the morning.

The Plasma Prolactin Levels in Man During Prolongation of Darkness in the Morning

“…The stress may have been more intense during the control period, which in all subjects preceded the experimental period. How¬ ever, it is conceivable that the stress was more intense during the experimental period when the subjects remained in complete darkness for an extra 4 h. Furthermore, the average levels of 11-hydroxycorticosteroids during both periods of investigation were similar, which indicated that the possible dif¬ ference in stress was minimal (Osterman 1974).…”

“…The negligible influence of changes in the dark-light pattern, on the synchronization of the sleep-related changes in the prolactin level, contrasts with the findings of studies on the circadian plasma cortisol rhythm. In man the dark-light transition seems to be important for the synchronization of the circadian plasma cortisol rhythm (Orth Sc Island 1969;Osterman 1974).…”

“…Further details about the experimental design are given in a recent report, which deals with the level of plasma 11-hydroxycorticosteroids in the same experiment (Osterman 1974).…”

A Comparison of 06:00 AM Versus 09:00 AM Serum Cortisol as a Basal Morning Cortisol in Guwahati, Assam: A Pilot Study

“…Cortisol secretion is regulated by the circadian rhythm, which is influenced by external cues called zeitgebers, such as light-dark cycle,[ 5 6 ] awakening[ 7 ] and social cues. [ 8 ] Light, in particular, plays a crucial role in the entrainment of the circadian rhythm.…”