Melatonin is one of the hormones secreted by the pineal gland in the brain. Melatonin is also known as pineal hormone, melatonin, melatonin hormone. It is stored in the pineal body after melatonin is synthesized, and sympathetic nerve excitation innervates the pineal cells to release melatonin. The secretion of melatonin has a distinct circadian rhythm, with suppressed secretion during the day and active secretion at night.