Melatonin secretion by the pineal gland has circadian rhythmicity regulated by the suprachiasmatic nucleus (SCN) found in the brain.
[4] Melatonin receptors are found throughout the body in places such as the brain, the retina of the eye, the cardiovascular system, the liver and gallbladder, the colon, the skin, the kidneys, and many others.
The two scientists obtained extracts of the pineal gland from bovines and noticed its blanching effects on the skin of tadpoles.
[10] Also, regulation of addictive behavior has been associated with the increase of melatonin receptor-related cAMP in the mesolimbic dopaminergic system.
[5] Melatonin treatment has also been studied as a remedy of disturbed circadian rhythms found in conditions such a jet lag, shift work, and types of insomnia.
[14] Melatonin's action in the retina is believed to affect several light-dependent functions, including phagocytosis and photopigment disc shedding.
Activation of the MT2 receptor promotes vasodilation which lowers body temperature in the extremities upon daytime administration.
[5] The most notable of the functions that are largely mediated by the MT2 receptor is that of phase shifting the internal circadian clock to entrain to the Earth's natural light-dark cycle.
Binding of melatonin to the MT1 receptor leads to inhibition of cAMP production and Protein Kinase A (PKA).
[11] These responses help the MT2 receptor accomplish its role in phase shifting the circadian clock by adjusting the sensitivity and availability of the population of MT2 to melatonin.
The behavior of each of these receptors under prolonged exposure to their chief agonist - melatonin - is indicative of the functions that they are each crucial to.
[11] This functional diversity of melatonin receptors helps give the SCN the ability to not only keep near 24-hour time and entrain to an exactly 24-hour period, but also regulate, among other factors, wakefulness and activity throughout this cycle.
Many people who struggle with falling asleep utilize melatonin supplements to help induce the onset of their sleep.
[citation needed] Irregular/arrhythmic melatonin levels has, in addition to cancer, been linked to development of cardiovascular disease.