Relationship Between Gh Secretion And Sleep In Pathological States

In untreated acromegaly, studies that have examined the GH profile during poly-graphically recorded sleep have reported the absence of sleep-related GH pulses despite the presence of SW sleep (80,81).

A few studies have examined nocturnal GH secretion in patients with obstructive apnea before and after treatment (82-84). As expected, nocturnal GH release is decreased in untreated apneic subjects. Because adult patients with this pathology are frequently obese, the low overnight GH levels could reflect the hyposomatotropism of obesity, rather than result from the shallow and fragmented nature of their sleep. However, two studies that have examined the nocturnal GH profile before and after treatment with continuous positive airway pressure (CPAP) have demonstrated that treatment of the sleep disorder resulted in a clear increase in the amount of GH secreted during the first few hours of sleep (83,84). An example is illustrated in Fig. 7. In children, surgical correction of obstructive sleep apnea may restore GH secretion and normal growth rate (82).

In obese subjects who do not have sleep apnea, a normal relationship between the first SW episode and GH release may be observed both during nocturnal sleep and during

Fig. 7. Mean (+SEM) nocturnal plasma GH profiles in patients with sleep apnea before (top) and after (bottom) CPAP treatment. Black bars represent the scheduled sleep periods. Data source: ref. 83.

daytime recovery sleep after sleep deprivation but, as expected, the amount of GH secreted in the sleep onset pulse is markedly decreased as compared to nonobese control subjects (85).

In a recent study in which polysomnographic recordings and hourly GH levels were obtained for 24 h in African patients infected with trypanosomiasis (i.e., African sleeping sickness), significant correlations between plasma GH levels and SW sleep were iden-titled despite the fact that the temporal distributions of both sleep and GH secretion across the 24-h cycle were markedly disrupted (86).

A number of studies have examined sleep quality and GH secretion in depression and have generally observed a decrease in nocturnal GH release as well as a reduced amount of SW sleep, although quantitative relationships between the magnitude of these two alterations were not demonstrated and cause-effect associations remain elusive (38,87,88).

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