Melatonin, which shows a robust nycthemeral rhythm, plays the role of an endogenous synchronizer, able to stabilize and reinforce circadian rhythms and maintain their mutual phase relationships. Additionally, melatonin is a potent antioxidant and displays immunological properties. Because free radical generation, immune dysfunction, and sleep and metabolic disorders are involved in the short- and long-term pathophysiology of the burn syndrome, we undertook the study of daily urine melatonin, 6-sulfatoxymelatonin (aMT6s, the main hepatic melatonin metabolite), and cortisol variations plus temperature profiles in burn patients using a non-invasive protocol. Eight patients (6 males, 2 females) were studied on three occasions after admission to the intensive care unit (early session: days 1 to 3; intermediate session: day 10; late session: days 20 to 30). Melatonin, aMT6s, and free cortisol levels were determined in urine samples collected at 4 h intervals over a continuous 24 h span. Core temperature was recorded daily. Controls consisted of healthy subjects in the same age range. Cosinor analysis of the data provided an evaluation of mesor, amplitude, and acrophase of circadian rhythms. Also, we calculated day (D), night (N), and 24 h hormone excretions, N/D ratio for melatonin and aMT6s, and D/N ratio for cortisol. These data were analyzed using Kruskal-Wallis test followed by multiple comparisons. Cosinor analysis did not detect a circadian rhythm in melatonin, aMT6s, or cortisol in any of the three sessions. D melatonin excretion displayed a major increase, resulting in a decreased N/D melatonin ratio, and the melatonin mesor (24 h mean) was increased in the early session, compared with controls. For aMT6s, only the early N/D ratio was decreased, and the mesor of the intermediate session increased. These results were not the consequence of hepatic and/or kidney alteration, as the patients' hepatic and renal parameters were in the normal range. The D and N melatonin/aMT6s ratios of controls and patients were similar, and the aMT6s profiles were superimposed on the melatonin ones, mainly during the day. The D, N, and 24 h cortisol values were increased in all sessions, except for the D level of the early session. The consistently increased mesors in the three sessions provided confirmation. The core temperature profiles were abnormal in all three sessions, mainly during the night, although there was a tendency toward normalization with time. The individual mesors were consistently increased compared with controls. Globally, the abnormalities we report could participate in the pathophysiology of short- and long-term alterations observed in burn syndrome, especially disturbances of sleep, metabolism, and immune function.
