Gender differences in the temporal organization of proclactin (PRL) secretion: evidence for a sleep-independent circadian rhythm of circulating PRL levels- a clinical research center study.

Abstract

Although a nocturnal rise in PRL secretion is well known, it has long been presumed to be evoked by sleep. To determine whether PRL secretion was driven by a sleep-independent circadian rhythm, we studied 12 men and 10 women using a constant routine protocol. Under the constant routine conditions of continuous semirecumbent wakefulness in constant indoor room light with hourly meals distributed throughout the day and night, a persistent circadian rhythm of PRL secretion was present in men and in women at the follicular and luteal phases of the menstrual cycle. Furthermore, the amplitude of this rhythm in women was significantly greater than that in men. The present data demonstrate the presence of a robust sleep-independent endogenous circadian rhythm of PRL secretion in humans. We hypothesize that this endogenous component of the circadian rhythm of PRL secretion together with those of body temperature, urine production, and cortisol, TSH, and melatonin secretion are driven by the central circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus.

Sleep and Circadian Rhythms in Humans

“…In humans, many aspects of human physiology and behavior vary with circadian phase (Czeisler and Jewett 1990;Johnson et al 1992;Allan and Czeisler 1994;Waldstreicher et al 1996;El-Hajj Fuleihan et al 1997;Cajochen et al 1999;. Thirty-five years ago, the central neuroanatomic structures responsible for both the generation of endogenous circadian rhythms and their synchronization with the 24-hour day were identified (Moore 1972;Moore and Eichler 1972;Moore and Lenn 1972;Stephan and Zucker 1972 Brigham and Women's Hospital, Boston, Massachusetts 02115 During the past 50 years, converging evidence reveals that the fundamental properties of the human circadian system are shared in common with those of other organisms.…”

From Galactorrhea to Osteopenia: Rethinking Serotonin–Prolactin Interactions

“…PRL release follows a circadian rhythm, with increased secretion in the early evening hours (Sassin et al, 1972;Waldstreicher et al, 1996). Peak PRL levels occur in the early morning secondary to its increased secretion with prolonged sleep.…”

Light Treatment and Circadian Adaptation to Shift Work

“…The major peak of GH secretion is normally observed around sleep onset [38][39][40][41][42][43][44] , even when the sleep episode is delayed 42,45) . Sleep exerts a strong stimulant effect on PRL secretion [46][47][48][49] , and peak PRL levels are observed during the later part of the sleep episode 47,50,51) . A rapid shift in a typical worker's bedtimes will be readily accompanied by a comparable shift in the secretory rhythms for GH and PRL 52,53) .…”