Human Melatonin ELISA Kit

Melatonin, an indoleamine hormone produced and secreted by pineal gland cells and extrapineal cells at night, plays an important role mainly in regulating human circadian rhythms and modulating sleep/wake cycles, and has attracted much attention in recent years because of its potent lipophilicity, antioxidant and free radical scavenging effects. Melatonin also exerts immunomodulatory effects by stimulating high-affinity receptors expressed in immunoreactive cells. Mammalian melatonin is secreted primarily by the pineal gland and is regulated by the supraoptic nucleus of the hypothalamus, a process that is light-inhibited and generally synthesized at night. In addition, melatonin secretion by some extrapineal cells (in the gastrointestinal tract, ovaries, lymphocytes, and skin) is not affected by the circadian cycle. Extrapineal melatonin produces paracrine or autocrine effects, superimposed on neuroendocrine hormone responses, and acts primarily as a local antioxidant.

Melatonin is derived from tryptophan, which is converted to serotonin after hydroxylation and decarboxylation reactions, which is then converted to melatonin in two successive reactions catalyzed by enzymes. SNATase deficiency and tryptophan deficiency are two limiting factors in the melatonin synthesis pathway, and seasonal changes in temperature and photoperiod significantly affect melatonin production in humans. Synthesized melatonin has a short half-life and diffuses immediately into the blood and cerebrospinal fluid (CSF), and due to its lipophilic and hydrophilic properties, it diffuses readily through cell membranes and can be detected in other body fluids. Melatonin is unevenly distributed in the body, with higher concentrations in the CSF than in the blood, but changes in blood melatonin levels are usually used to represent changes in systemic levels. Oral administration of 0.1-0.3 mg melatonin achieves physiologic concentration ranges, and even when doses well in excess of physiologic concentrations are taken, no significant toxic reactions have been noted.

Figure 1. Melatonin biosynthesis and intracellular signal-transduction pathways activated by stimulation of melatonin specific receptors
(Source: Ferlazzo N, et al. 2020)

The main targets of endogenous melatonin are two G-protein-coupled receptors, MT1 and MT2, which have a high affinity for being activated by circulating levels of melatonin at night and subsequently activate or inhibit downstream signaling pathways to exert a variety of physiological effects. The signaling pathways activated by MT receptors are highly dependent on cells and tissues, but also on different proteins that form heterodimeric complexes with MT receptors. These characteristics underlie the multiple effects of melatonin in the human body, which can be viewed both as regulation of key metabolic processes and as protection against a variety of diseases.