The role of melatonin
Melatonin, the hormone secreted by the pineal gland, takes part in the regulation of sleep and circadian rhythm. Measurement of 6- sulfatoxymelatonin (6-SMT), which is a melatonin metabolite and is excreted with urine, reflects secretion of melatonin in healthy subjects.
The concentration of plasma melatonin though is more informative in critically ill patients with multi-organ failure.
Melatonin secretion is described suppressed in critically ill patients. Shilo et al. has studied day secretion of melatonin in a group of intensive care patients compared to a group of patients from ordinary medical wards.
He found a missing nocturnal top of melatonin in all intensive care patients but
two, and these did not require ventilator therapy.
Melatonin secretion was estimated from 6-SMT in urine samples, collected every third hour during 24 h.