Description
The major hormone of the pineal gland is N-acetyl-5-methoxy-tryptamine or melatonin, which is synthesized from the amino acid tryptophane.
The pineal gland (corpus pineale) has been called a neuroendocrine transducer because of its important role in photoperiodism. Melatonin has its highest levels in plasma during nighttime. Regulation of the melatonin secretion is under neural control. Sympathetic innervation seems to play a major role via its release of noradrenaline. Altered patterns and/or levels of melatonin secretion have been reported to coincide with sleep disorders, jet lag, depression, stress, schizophrenia, hypothalamic amenorrhea, pregnancy, anorexia nervosa, some forms of cancer, immunological disorders as well as control of sexual maturation during puberty. Salivary melatonin is a useful biomarker in circadian dysregulation through shift work or exposure to bright light at night. Most of the circulating melatonin is metabolized in the liver to 6-hydroxymelatonin and subsequently to 6-sulfatoxymelatonin, which is excreted into the urine. The concentration of 6-hydroxymelatonin sulfate in urine correlates well with the total level of melatonin in the blood during the collection period.
