Melatonin

Melatonin (from Greek melas = dark colored, tonos = tension) is a hormone that is formed in the epiphysis (pineal gland hormone) of vertebrates and humans from serotonin through N-acetylation (see N-acetyl transferases) and 5-methylation. Further production sites of melatonin are the retina and the intestine.

With versch. In various fishes and amphibians, melatonin as the antagonist of melanotropin induces a concentration of melatonin in the cells and thus causes a lightening of the skin.

In birds and mammals, melatonin formation follows a circadian rhythm (chronobiology).

Thus the melatonin concentration increases during the night. The maximum peak is reached around 3 a.m. The melatonin-induced deep sleep phase stimulates the release of the growth hormone somatropin (STH). Corresponding chronic disorders lead to premature cessation of somatotropin production.

Melatonin production is reduced by daylight. In darkness, the production and secretion of melatonin increases again. The enzyme responsible for the final synthesis step, hydroxyindole-O-methyltransferase, is less active during the day than at night (probably caused by a rhythmically activated gene expression for this enzyme).

Melatonin thus plays an important role in the coordination of circadian-rhythmic processes in the organism. It plays an important role as a timer.

Furthermore, melatonin lowers the secretion of the luteinizing hormone (LTH), thus preventing sexual maturation processes. Especially a reduction (but also an increase) of the melatonin level causes sleep disorders or disturbances of the sleep-wake rhythm.

1. Asghari MH et al (2016) A review of the protective effect of melatonin in pesticide-induced toxicity. Expert Opinion Drug Metab Toxicol 29:1-10.
2. Williams WP 3rd et al. (2016) Comparative Review of Approved Melatonin Agonists for the Treatment of Circadian Rhythm Sleep-Wake Disorders. Pharmacotherapy doi: 10.1002/phar.1822.