On the time course of thyrotropin suppression by high doses of thyroid hormones.

Basal and stimulated TSH decreased progressively. Basal TSH was suppressed below the detection limit of 0.4 muU/ml after 74 h in 2 of the T3 and all of the T4 treated individuals. At this time in both groups 3 individuals could be significantly stimulated by TRH (abour 5% of the pretreatment stimulation). There was no significant difference in the time course of suppression obtained by T3 or T4 through plasma T3 levels in the T4 treated group were considerably lower.