Thyrotropin suppressive therapy and TSH rhythm

TSH circadian secretion rhythm and its changes after the response after exogenous TRH administration were evaluated in 7 patients, affected by simple goiter, after diurnal (h 7.00) and nocturnal (h 19.00) administration of l-thyroxine (1.8-2.2 μg/kg). TSH surge after nocturnal administration of l-thyroxine was higher than TSH surge diurnal administration (18.75 ± 3% v.s. 113.9 ± 17.2%; P < 0.001). Besides, the increase of TSH response to TRH after nocturnal administration of l-thyroxine was higher than increase after diurnal administration. These results show the need to administer l-thyroxine in the morning (7.00 h) to obtain the best suppressive effect on thyroid gland.