Part of “CHAPTER 6 – ENDOCRINE RHYTHMS“

In normal adult men and women, TSH levels are low throughout the daytime and begin to increase in the late afternoon or early evening.61 Maximal levels occur shortly before sleep. During sleep, TSH levels generally decline slowly. A further decrease occurs in the morning hours (see Fig. 6-2 and Fig. 6-6). Studies involving sleep deprivation and shifts of the sleep-wake cycle have consistently indicated that an inhibitory influence is exerted on TSH secretion during sleep. Interestingly, when sleep occurs during daytime hours, TSH secretion is not suppressed significantly below normal daytime levels. When the depth of sleep is increased by prior sleep deprivation, the nocturnal TSH rise is even further blunted. There is a consistent association between descending slopes of TSH concentrations and SW stages.62 The pronounced enhancing effect of sleep deprivation on the nighttime TSH rise is illustrated in Figure 6-2. The timing of the evening rise seems to be controlled by circadian rhythmicity. The temporal pattern of TSH secretion seems to reflect both tonic and pulsatile release, with both the frequency and the amplitude of the pulses increasing during the nighttime. Pulses of TSH secretion persist during somatostatin or dopamine treatment, suggesting that the control of pulsatility is largely thyrotropin-releasing hormone dependent.61