Occurrence
Melatonin is a naturally occurring hormone in the body.
Definition
ChEBI: A member of the class of acetamides that is acetamide in which one of the hydrogens attached to the nitrogen atom is replaced by a 2-(5-methoxy-1H-indol-3-yl)ethyl group. It is a hormone secreted by the pineal gland in humans.
World Health Organization (WHO)
Melatonin is promoted as a cure for travel sickness, jet-lag and
insomnia and has recently been claimed in the United States to reverse the ageing
process. A synthetic version has been freely available from health food shops and
pharmacies as a "nutritional supplement" since 1993.
General Description
A hormone that has been postulated as being a mediator of photic-induced anti-gonadotropic activity in photoperiodic mammals. Counteracts the apoptotic effects of etoposide in bone marrow cells. Melatonin receptors are coupled to a G-protein system. Inhibits rat cerebellar nitric oxide synthase (NOS).
Biochem/physiol Actions
Hormone; mediates photoperiodicity in mammals; inhibits cerebellar nitric oxide synthetase; peroxynitrite scavenger. Melatonin has complex effects on apoptotic pathways, inhibiting apoptosis in immune cells and neurons but enhancing apoptotic cell death of cancer cells. Inhibits proliferation/metastasis of breast cancer cells by inhibiting estrogen receptor action.
Clinical Use
Melatonin is most effective in young individuals and appears to be less effective in elderly individuals (possibly because of a decreased number of receptors). Melatonin causes a phase shift of approximately 1 hour per day. This means that the use of melatonin in the morning can delay the onset of evening sleepiness, whereas melatonin taken in the evening has been associated with faster onset of sleep and increased total sleep time. Melatonin is sold as a food supplement in the United States, but it has become popular for use as a hypnotic and for alleviating jet lag (a flight across five or more time zones) and helping to resynchronize individuals who have difficulty adapting to night-shift work. have effects on circadian rhythm and sleep processes. The presence of a pharmacologically specific receptor for melatonin in which the molecular structure is known are referred to as MT1, MT2, and MT3 receptors. The MT1 and MT2 receptors are high-affinity G protein coupled receptors, whereas MT3 is a form of quinone reductase. The MT1 receptor appears to be primarily involved in initiating sleep, whereas the MT2 receptor appears to mediate melatonins effect in the eye, circadian rhythm, and vascular effects. The importance of MT3, although widely distributed in different tissues, is currently unknown. The normal physiological concentration of melatonin observed at night is approximately 100 to 200 pg/mL, and oral doses of 0.1 to 0.3 mg of melatonin are adequate to obtain these concentrations even though melatonin frequently is given at doses of 1 to 10 mg to obtain supraphysiological levels. These higher doses may be the reason for some of the side effects not currently associated with the melatonin receptors.
Veterinary Drugs and Treatments
Melatonin may be useful to treat Alopecia-X in Nordic breeds, canine
pattern baldness, or canine recurrent flank alopecia in dogs.
It has been used anecdotally for the treatment of sleep cycle disorders
in cats and geriatric dogs and to treat phobias and separation
anxiety in dogs. Melatonin implants are used in the mink and fox
pelt industries to promote the development of luxurious hair coats.
Implants are also used to improve early breeding and ovulation
rates in sheep and goats. Preliminary research is being done for this
purpose in horses also.
In pigs, one study (Bubenik, Ayles et al. 1998) demonstrated that
5 mg/kg in feed reduced the incidence
of gastric ulcers in young
pigs.
