Nocturnal melatonin plasma levels in patients with obstructive sleep apnoea syndrome: the effect of continuous positive airway pressure

¹ Service of Pneumology and; and Research Unit, Hospital Universitario de Canarias
² Dept of Physiology, Faculty of Medicine, University of La Laguna, La Laguna, Tenerife, Spain
³ Service of Pneumology and
⁴ Research Unit, Hospital Universitario de Canarias

^* To whom correspondence should be addressed. E-mail: chernandezg{at}teleline.es.

	Abstract

Melatonin is a pineal hormone that regulates the human cycle of sleep and wakefulness. Plasma melatonin levels were investigated in patients with Obstructive Sleep Apnoea Syndrome (OSAS).

Twenty patients with OSAS and eleven healthy controls were studied. OSAS patients were tested twice: the night of the diagnostic polysomnography and the night of the continuous positive airway pressure (CPAP) titration. Controls were tested on one occasion. Plasma melatonin levels were determined at 23:00 (light period), at 02:00 (dark period) and at 06:00 (light period) in patients and control subjects using the radioimmunoassay method.

The control subjects showed a nocturnal melatonin peak value at 02:00 (70.6±14 pg·ml^-1). However, this nocturnal melatonin peak was absent in the OSAS patients. The highest melatonin value was found in OSAS patients the night of diagnosis, at 06:00 (49.3±36.8 pg·ml^-1). We found that the melatonin level at 06:00 was significantly lower in the titration night (35.6±37.9 pg·ml^-1) than in the diagnosis night (p<0.05) in OSAS patients. The melatonin levels at 23:00 and at 02:00 did not differ significantly comparing the OSAS patient's levels in the night of diagnostic polysomnography (23:00: 31.6±29.8 pg·ml^-1; 02:00h: 47.4±33.8 pg·ml^-1) with levels in the night of CPAP titration (23:00: 20.2±10.3 pg·ml^-1, 02:00: 37.7±27.5 pg·ml^-1).

Patients with OSAS have an abnormal melatonin secretion pattern. The absence of a nocturnal serum melatonin peak could partially be related to the difficulty that these patients have to achieve a normal sleep-wakefulness pattern.