Circadian and sleep-related endocrine rhythms in schizophrenia

Plasma levels of prolactin, growth hormone, corticotropin, and cortisol were measured at 15-minute intervals for 24 hours in nine unmedicated male schizophrenic patients and in nine age-matched normal male subjects. Each study was preceded by 3 days of habituation to the laboratory environment. Sleep was polygraphically recorded. The circadian and pulsatile variations present in each hormonal profile were quantitatively characterized with the use of computer algorithms specifically designed for analyses of hormonal fluctuations. The major abnormality of neuroendocrine release that was observed in the schizophrenic patients was an almost threefold enhancement of the sleep-related increase in the prolactin level, associated with an intensified frequency of nocturnal prolactin pulses. This increased stimulatory effect of sleep on prolactin secretion was evident immediately after sleep onset. The normal inhibition of cortisol secretion during early sleep was absent in schizophrenic patients. The major sleep abnormalities were a prolonged sleep latency and a reduction in total rapid eye movement stage sleep. During wakefulness, prolactin and cortisol levels were normal. The 24-hour profile of growth hormone was unaltered in schizophrenic patients, and a sleep-onset growth hormone pulse was observed in all patients. No abnormalities were noted in the levels or temporal organization of corticotropin secretion. Both the amplitude and the timing of the cortisol rhythm were normal. We conclude that, in schizophrenic men, pituitary-adrenal function and circadian time-keeping are normal but prolactin secretion is hyperresponsive to the physiologic stimulus of sleep onset. Schizophrenia thus appears to be characterized by a subset of neuroendocrine disturbances distinct from that observed in major endogenous depression.