Central nervous system control of thyrotropin secretion during sleep and wakefulness.

Thyrotropin (TSH) is a pulsatile secreted hormone with a pronounced circadian rhythmicity and a characteristic nightly surge based on an augmentation of pulsatile release. A number of physiological factors influence TSH secretion via an alteration in the amount of pulsatile released hormone. An increase in somatostatinergic tone during fasting appears to decrease TSH pulse amplitude and sequentially mean TSH serum levels. In contrast, blockade of dopaminergic tone by metoclopramide infusion when circulating TSH levels are low during the afternoon hours increase TSH pulse amplitude to levels comparable to the nightly TSH surge suggesting a physiological dampening of TSH pulse amplitude by dopamine during the daytime.