La melatonina actúa a través de receptores de alta afinidad que se ubican a nivel central y en numerosos órganos periféricos. El ritmo circadiano de la producción y liberación de melatonina, que se caracteriza por una actividad nocturna y un repose diurno, constituye una importante señal temporal para las estructuras del cuerpo que pueden leerla. La melatonina (MEL) es una hormona que es sintetizada y secretada por la glándula pineal, la cual se ubica en la profundidad del cerebro, en respuesta a señales fotoperiódicas que se transmiten desde la retina a través de un oscilador circadiano que está en el núcleo supraquiasmático del hipo tálamo. As for potential therapeutic applications, exogenous melatonin or a melatonin agonist and selective 5-hydroxytrypiamine receptor (5-HT 2c) antagonist, eg, S 20098, can be used to manipulate circadian processes such as the sleep-vake cycle, which are frequently disrupted in many conditions, most notably seasonal affective disorder.

However, their physiological role remains unelucidated, although livestock management applications already include the control of seasonal breeding and milk production. Different receptor subtypes have been cloned and characterized: MT 1 and MT 2 (transmembrane G-protein-coupled receptors), and MT 3. Melatonin acts through high-affinity receptors located centrally and in numerous peripheral organs. The circadian rhythm of melatonin production and release, characterized by nocturnal activity and daytime quiescence, is an important temporal signal to the body structures that can read it. Melatonin (MEL) is a hormone synthesized and secreted by the pineal gland deep within the brain in response to photoperiodic cues relayed from the retina via an endogenous circadian oscillator within the suprachiasmatic nucleus in the hypothalamus.

Farsky distinguish day and night