EPISODIC HORMONE-RELEASE IN RELATION TO REM-SLEEP

Similar periodicities of about 90-100 min characterize both hormone pulsatility and NREM-REM sleep cycles suggesting that both processes could be temporally linked. From the current knowledge of the literature, it appears that, in spite of the diversity of the relationship between hormones and the sleep/wake cycle, systematic relationships exist between hormone pulses and the NREM-REM sleep cycles. Early studies have demonstrated the temporal association between GH and SWS episodes occurring soon after sleep onset. Renin, a key enzyme of the renin-angiotensin system, displays nocturnal oscillations that are associated strongly with the NREM-REM sleep cycles, and represents the first identified biological marker of sleep stage alteration. SWS invariably occurs in the descending phases of TSH and cortisol pulses which suggests that some specific mechanisms of this sleep stage could modulate their levels or, conversely, that increased TSH and cortisol secretion prevents the occurrence of deep sleep. Apart from the period of sleep onset associated with reduced prolactin secretion, no systematic relationship has been found between REM sleep and hormone release. These results highlight the complexity of hormone and sleep interactions and provide a basis for further research into their functional significance.