The measurement of plasma melatonin levels by high performance liquid chromatography

Introduction Melatonin (N-acetyl-5-methoxytryptamine) is synthesized from tryptophan and it is a neurohormone which is secreted from the pineal gland of all mammals [1, 2]. Tryptophan, which is a melatonin precursor, is hydroxylated in the cells and turned into 5-hydroxytryptophan. Then this is decarboxylated and turned into serotonin (5-hydroxytryptamine). Serotonin is acetylated by arylalkylamine n-acetyltransferase (AA-NAT) enzyme to form N-acetylserotonin. N-acetylserotonin turns into melatonin by hydroxyindole-Omethyltransferase (HIOMT) [3]. Melatonin synthesis is affected by periods of light and dark, and the maximum secretion occurs between 2 to 4 a.m. in the night [4, 5]. The release also varies depending on age and season. Recent studies show that melatonin not only affects the immune system, but also has antioxidant, anti-apoptotic, anticarcinogenic, anti-aging properties [4]. There are many methods for the measurement of melatonin. Some of these methods are radioimmunoassay (RIA), gas chromatography-mass spectrometry (GC-MS), enzyme-linked immunesorbent assay (ELISA) and high performance liquid chromatography (HPLC). Among these methods GC-MS is the most sensitive and selective one. However, because of the long sample preparation and being too expensive, this method is not practical for routine use [6]. In this study, we propose to use HPLC method because of its high sensitivity and selectivity. The method is also easily applied and cheaper than the other methods.