Background Melatonin (MT) is secreted by the pineal gland and a circadian rhythm of MT secretion is related to light-darkness exposure. MT has been found to influence immune and endocrine functions and is a free radical scavanger. Immune abnormalities and disturbed endocrine secretion have been reported in patients with systemic sclerosis (SSc). Additionally, some of the patients have sleep disturbances or depression, a factors known to effect the MT level. All these findings suggest possible role of MT in pathogenesis of some phenomena seen in SSc patients.
Objectives The aim of the study was to evaluate the circadian profile of serum MT levels in patients with SSc.
Methods Six women with definite SSc, aged 32.4+1.8 yrs (symptoms duration 4–7 yrs) and six age-matched healthy women were investigated. Blood samples were drawn at 8.00, 12.00, 16.00, 20.00, 22.00, 24.00, 02.00, 04.00. 06.00. Light exposure of the subjects was from 07.30 to 21.00. MT was determined with ELISA method.
Results A significant circadian rhythm of serum MT was detected in all investigated subjects. Serum MT levels were lower in the SSc patients than in the controls, MESOR = 21.4 pg/ml and 47.3 pg/ml, in the patients and controls, respectively. In the SSc patients, the night increase in MT was also relatively lower when compared to the daily levels. Maximal values were found between 02.00–04.00 both in the patients and controls.
Conclusion The general nature of the circadian serum MT rhythm is maintained in the SSc patients although secretion of MT is depressed. The mechanism of impaired MT secretion remains unknown. It may be speculated that a low MT level is involved in development of immune abnormalities, neuroendocrine disfunctions and/or impaired free radical elimination. All these phenomena may contribute to development of fibrosis.
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