Sleep and Endocrinology: Hypothalamic-pituitary- adrenal axis and growth hormone.
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Date
2013-07
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Abstract
The supra-chiasmatic nucleus (SCN) is the primarily biological clock determining the
circadian rhythm. The neurons of the nucleus making this clock have inherent rhythm
and set in biological day and night. These periods usually corresponds to day/night, and
indirectly to sleep-wakefulness cycle, in most individuals. Retino-hypothalamic tract
carrying photic information from the retina provides the most important input to
maintain the inherent rhythm of the SCN. The rhythmic discharges from the SCN to
various neurons of the central nervous system, including pineal gland and
hypothalamus, translate into circadian rhythm characteristic of several hormones and
metabolites such as glucose. As a result there is a pattern of hormonal changes
occurring during cycle of sleep wakefulness. Most characteristic of these changes are
surge of melatonin with biological night, surge of growth hormone-releasing hormone
(GHRH)at onset of sleep and surge of corticotropin-releasinghormone(CRH)
during late part of the sleep. The cause and effect relationship of the hypothalamic
releasing hormones and their target hormones on various phases of sleep including
initial non rapid eye movement (NREM) phase at onset of sleep, and rapid eye
movement (REM) phase near awakening, is an upcoming research area. Sleep
electroencephalogram (EEG) determining the onset of NREM and REM sleep is an
important tool complimenting the studies assessing relationship between various
hormones and phases of sleep. The slow wave activity (SWA) corresponds to the
intensity of sleep at its onset during the biological night of an individual. Besides,
GHRH and CRH, several other peptide and steroid hormones such as growth
hormone (GH), its secretagogues, ghrelin, neuropeptide Y, estrogen and
dehydroepiandrosterone sulfate are associated or have the potential to change phases of
sleep including initial slow wave-NREM sleep.
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Goswami Ravinder. Sleep and Endocrinology: Hypothalamic-pituitary- adrenal axis and growth hormone. Annals of the National Academy of Medical Sciences (India). 2013 Jul-Dec; 49(3&4): 177-184.