Melatoniini

Melatoniini, or melatonin, is a hormone produced primarily by the pineal gland in humans and other vertebrates. It is synthesized from serotonin through the sequential action of the enzymes arylalkylamine N-acetyltransferase (AANAT) and hydroxyindole O-methyltransferase (HIOMT). Production follows a circadian rhythm and is highest during the night.

Secretion is regulated by the light-dark cycle: light exposure suppresses melatonin release via retinal input to the suprachiasmatic nucleus, while darkness stimulates synthesis. Melatonin promotes sleepiness and helps synchronize circadian rhythms by acting on melatonin receptors MT1 and MT2 in the brain and other tissues.

In addition to sleep regulation, melatonin has antioxidant properties and may modulate immune function. In animals it also influences seasonal reproduction; in humans, evidence for these roles is less certain.

Clinical use and safety: In many countries melatonin is available as an over-the-counter supplement. It is used to treat jet lag, circadian rhythm sleep disorders, and some insomnia. Dosing commonly ranges from 0.5 to 5 mg taken before bedtime. Side effects are generally mild but can include drowsiness, dizziness, and headaches. Caution is advised for people taking anticoagulants, diabetes medications, immunosuppressants, or hormonal therapies. Long-term safety data are limited.

Pharmacokinetics and metabolism: Melatonin is rapidly absorbed, with peak levels occurring within about an hour and a half-life of roughly 20–50 minutes. It is mainly metabolized in the liver by CYP1A2 and excreted as metabolites in urine.

History: Melatonin was first isolated in 1958 by Aaron B. Lerner. It has since become a widely studied signaling molecule in circadian biology.