Melatonina i jej receptoryMelatonin and melatonin receptors

摘要

The pineal hormone melatonin (N-acetyl-5-metoxytryptamine) is an important regulator of seasonal reproduction and cireadian rhythms. Melatonin is synthesized from serotonin, primarily in the pineal gland. The circadian production of melatonin from the mammalian pineal gland is endogenously controlled by the suprachiasmatic nucleus of the hypothalamus, the site of the mammalian cireadian pacemaker, and is synchronized by environmental light. In all vertebrates, melatonin is secreted from the pineal gland during the hours of darkness and acts as a hormonal message of the photoperiod. Its effect is mediated via high-affinty melatonin receptors. Two subtypes of mammalian melatonin receptors have been cloned and characterized: the T1 (Mel1a) and the MT2 (Mel1b) melatonin receptor subtypes. Both subtypes are members of the G protein-coupled receptor family. A third subtype of the high-affinity melatonin receptor was cloned from a chicken brain and termed the Melle. Mammalian MT1 is expressed in the hypophyseal pars tuberalis and hypothalmic suprachiasmatic nuclei, the regions of the brain that have been implicated as being important for reproduction and circadian rhythms. MT2 is found in the retina.