CENTRAL-NERVOUS-SYSTEM CONTROL OF THYROTROPIN SECRETION DURING SLEEP AND WAKEFULNESS

Thyrotropin (TSH) is a pulsatile secreted hormone with a pronounced ci rcadian rhythmicity and a characteristic nightly surge based on an aug mentation of pulsatile release, A number of physiological factors infl uence TSH secretion via an alteration in the amount of pulsatile relea sed hormone, An increase in somatostatinergic tone during fasting appe ars to decrease TSH pulse amplitude and sequentially mean TSH serum le vels. In contrast, blockade of dopaminergic tone by metoclopramide inf usion when circulating TSH levels are low during the afternoon hours i ncrease TSH pulse amplitude to levels comparable to the nightly TSH su rge suggesting a physiological dampening of TSH pulse amplitude by dop amine during the daytime.