RESTORATION OF DETECTABLE MELATONIN AFTER ENTRAINMENT TO A 24-HOUR SCHEDULE IN A FREE-RUNNING MAN

We evaluated a 37-year-old male with a non-24-h sleep-wake disorder. H is environment gave him little exposure to bright light. Circadian pro files of temperature, melatonin, thyrotropin, cortisol and testosteron e were obtained along with endocrine challenges of the thyroid, adrena l, growth hormone and gonadal axes. Multiple endocrine abnormalities w ere detected. Testosterone was low and nocturnal thyrotropin levels we re erratic. Serum melatonin was undetectable throughout the day and ni ght on multiple occasions, and responses to infusions of TRH, GnRH and GRF-44 were abnormal. Responses to CRH infusion were normal. The pati ent was successfully entrained to a 24-h schedule by daily exposure to 2500 lux light from 0700h to 0900h, avoidance of light (by wearing da rk goggles) from 1800h to 2300h, and strict enforcement of a dark envi ronment from 2300h to 0700h. After entrainment, a normal pattern of no cturnal melatonin secretion was found. GH response to GRF-44 also norm alized, although abnormal responses to TRH and GnRH persisted. This ca se raises the possibility that a complex interaction of light exposure with the circadian system can reversibly suspend pineal gland secreti on of melatonin indefinitely. It also suggests that circadian rhythm d isorders be considered in the differential diagnosis of abnormal endoc rine function. Published by Elsevier Science Ltd.