Studies of TSH circadian rhythm in normal males and females

Our results confirm the presence of a significant secretory modification of TSH during the 24 h period; such a pattern is superimposable in both sexes, although significantly lower concentrations have been recorded in females. Our cases almost uniformly showed the highest TSH concentration around the onset of sleep, a decrease during the sleep and in some cases an increase at the awakening. This pattern seems to support the hypothesis of an inhibitory influence of sleep on TSH secretion (although this cannot explain the further decrease of TSH concentrations observed during the morning). This is only partially confirmed by the sleep-reversal experiments. It seems reasonable that TSH secretion is primarily determined by a rhythm, probably of hypothalamic origin, may be related to the light/dark cycles.