Melatonin, Serum/Plasma

N-acetyl-5-methoxy-tryptamine

Melatonin

Plasma (EDTA); Serum

The pineal gland has been called a neuroendocrine transducer because of its importance in photoperiodism. The major hormone of the pineal gland is Melatonin (N-acetyl-5-methoxy-tryptamine). It is the major indole compound synthesized by the pineal gland. It is converted from Serotonin by Hydroxy Indole-O-Methyl Transferase. It is excreted into the urine as 6-Sulfatoxymelatonin, N-Acetyl Serotonin, other glucuronide and sulfate forms, and also a small amount as unconjugated "free" Melatonin. Melatonin has potent melanocyte contracting properties. Melatonin is primarily secreted during the dark (night) cycle. Levels drop dramatically after exposure to bright light. Melatonin binds to various proteins including Albumin. Patients with cancer frequently have decreased levels of Melatonin as do patients with impaired central nervous system function. Elevated levels can be found in sympathetic orthostatic hypotension. Melatonin has a stimulatory and suppressive feedback on Gonadotropin release depending on Melatonin levels. Altered levels of Melatonin have been reported with sleep disorders, jet lag, depression, stress, schizophrenia, hypothalamic amenorrhea, pregnancy, anorexia nervosa, immunological disorders, as well as sexual maturation during puberty.