BIOCHEMISTRY A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site melatonin A hormone derived from serotonin and secreted by pinealocytes in the pineal gland and also by the retinas of vertebrates; it passes by way of the blood or through the fluid of the third ventricle to the anterior pituitary gland to control gonadotropic hormone secretion. Melatonin secretion by the pineal is linked to the dark-light cycle of the organism's environment, being greatest at night and lowest by day. It is involved in regulating certain diurnal and seasonal changes in the body, such as the onset and timing of sleep, winter weight gain, and the reproductive cycle in seasonally breeding animals. Melatonin also controls pigmentation changes; it triggers aggregation of the pigment melanin into melanophores in the skin, causing the skin to turn pale. Levels of melatonin decline with age. Melatonin (5-methoxy-N-acetyltryptamine) is naturally synthesized from the amino acid tryptophan (derived from serotonin) by the enzyme 5-hydroxyindole-O-methyltransferase. It can be manufactured artificially and has shown several possible beneficial medical uses. Related category    • BIOCHEMISTRY Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP