Melatonin secretion cycle

Melatonin secretion is synchronized to the light/dark (LD) cycle, with a nocturnal maximum (in young humans, about 200 pg/ml plasma) and low diurnal baseline levels (about 10 pg/ml plasma). Studies have supported the value of the exogenous administration of melatonin in circadian rhythm sleep disorders, insomnia, cancer, neurodegenerative diseases, disorders of the immune function, and oxidative damage (Karasek et al. 2002 Pandi-Perumal et al. 2005, 2006 Srinivasan et al. 2005a,b, 2006 Hardeland et al. 2006). 

The circadian pattern of pineal NAT activity and consequently melatonin secretion is controlled by the suprachiasmatic nuclei (SCN) as it is abolished by lesions of the SCN, the major circadian oscillator (Klein and Moore 1979). Thus, the environmental L/D cycle acts as the pervasive and pre-eminent Zeitgeber that regulates melatonin synthesis (Scheer and Czeisler 2005). 

There was suppression of endogenous melatonin secretion in two of five patients with bipolar disorder after 12 weeks of treatment with high-dose melatonin (10 mg/day) (19). One woman developed an unentrained sleep-wake cycle after melatonin was withdrawn (not previously a feature of her illness), which persisted for several months. 

SSRIs can cause insomnia and daytime somnolence however, the symptoms seem to reflect a sleep-wake cycle disorder. It is conceivable that disruptions in the normal pattern of melatonin secretion, particularly a delay in the normal early morning fall in plasma concentrations could be involved in the pathophysiology of these symptoms. The fact that fluvoxamine is the SSRI that is most likely... 

The permissive serotonin hypothesis proposes that serotonin (5-hydroxytryptamine or 5-HT) plays a critical role in modulating brain activity (e.g., stabilization of the catecholamine system and inhibition of dopamine [DA] release), and is low in both mania and depression. L-tryptophan or 5-HT deficiency and changes in the light-dark cycle may result in reduced melatonin secretion from the pineal gland that disrupts the sleep-wake cycle, alters circadian rhythms, and causes seasonal affective changes. ... 

Melatonin has been used to regulate the sleep-wake cycle and is used often to treat insomnia. It is not recommended during pregnancy and breast-feeding becanse of a lack of information abont its safety. Lower doses of melatonin (e.g., 0.1-1 mg at bedtime) are effective in initiating sleep higher doses may not improve the hypnotic effect. The rednction in daytime snnUght, which increases melatonin secretion, may exacerbate PMS in the winter this type of seasonal mood disorder may respond to phototherapy. Early sleep deprivation also may help to correct circadian rhythm disturbances in PMDD. ... 

The HPG axis is responsible for the cyclic hormone secretion that regulates and controls ovulation and plays a major role in menstruation-related disorders. The menstrual cycle is characterized by cyclic alterations in the production of gonadal hormones (estradiol and progesterone), pituitary hormones (gonadatropins, prolactin, growth hormone), melatonin, and cortisol and in temperature rhythms. Menstruation-related disorders are likely the result of a complex interaction between ovarian steroids and central neurotransmitters, neurohormones, and neuropeptides. The occurrence of physical... 

HT is converted to melatonin in the pineal gland under the influence of darkness, and its production is controlled by a circadian temperature rhythm and synchronized by the light-dark cycle. Several studies have reported reduced and earlier secretion of... 

Melatonin, a hormone secreted by the pineal gland that regulates circadian rhythms, including wake-sleep cycles, is biosynthesized by a process in which the first step is an enzyme-catalyzed transfer of the acetyl group from sulfur of acetyl coenzyme A to the —NH2 group of serotonin. 

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