Affiliations: Service de Radiopharmacie et Radioanalyse, Centre de
Médecine Nucléaire, Hôpital Neuro-Cardiologique, B.P. Lyon Montchat, 69394
Lyon Cedex 03, France | Service de Neurologie, Hôpital Neurologique, B.P.
Lyon Montchat, 69394 Lyon Cedex 03, France
Abstract: Melatonin (MLT) is a methoxyindole secreted principally by the pineal
gland. It is synthesized at night under normal environmental conditions. The
endogenous rhythm of secretion is generated by the suprachiasmatic nuclei and
entrained by the light/dark cycle. Light is able to both suppress or
synchronize melatonin production according to the light schedule. The
nycthohemeral rhythm of this hormone is determined by repeated measurement of
plasma of saliva MLT or urine sulfatoxymelatonin, the main hepatic metabolite.
Melatonin can be considered as the output (the hand) of the endogenous clock.
Since the regulating system follows central and sympathetic nervous pathways,
an abnormality at any level unspecifically modifies the melatonin secretion,
especially in patients with sympathalgia or dysautonomia. Melatonin plays the
role of an endogenous zeitgeber on sleep-wake cycle or core temperature.
Exogenous melatonin is able to influence the endogenous secretion of the
hormone according to a phase response curve. There are therapeutic implications
for this property in situations when biological rhythms are disturbed (jet-lag
syndrome, delayed sleep phase syndrome, insomnia in blind or elderly people,
shift-work). Improvement of pharmaceutical forms studied in controlled trials
under the responsibility of the medical community or development of melatonin
analogs could lead to decisive progress in this field.
