Melatonin receptors in humans: biological role and clinical relevance

In addition to its antioxidative effects melatonin acts through specific nuclear and plasma membrane receptors. To date, two G-protein coupled melatonin membrane receptors, MT1 and MT2, have been cloned in mammals, while the newly purified MT3 protein belongs to the family of quinone reductases. Screening studies have shown that various tissues of rodents express MT1 and/or MT2 melatonin receptors. In humans, melatonin receptors were also detected in several organs, including brain and retina, cardiovascular system, liver and gallbladder, intestine, kidney, immune cells, adipocytes, prostate and breast epithelial cells, ovary/granulosa cells, myometrium, and skin. This review summarizes the data published so far about MT1 and MT2 receptors in human tissues and human cells. Established and putative functions of melatonin after receptor activation as well as the clinical relevance of these findings will be discussed.