Thyroglobulin and thyroid hormone release after intravenous administration of bovine thyrotropin in man

To elucidate the mechanism of thyroglobulin (Tg) release in man, the effects of an iv injection of a submaximal dose of bovine TSH (bTSH) on the serum levels of Tg were compared with the effects on serum T3 and T4. After the administration of bTSH, short term kinetics (0-4 h) were studied in eight subjects receiving 0.5 IU bTSH and seven subjects receiving 1 IU bTSH. Serum Tg did not significantly increase in either of the short term studies. By contrast, serum T3 increased significantly and linearly after the administration of 0.5 and 1 IU bTSH; serum T4 also rose but only after 1 IU bTSH. Long term kinetics (0-120 h) were studied in seven additional subjects after the iv administration of 1 IU bTSH; serum bTSH was no longer detectable after 8 h. Maximum serum concentrations of T3 were obtained at about 4 h, maximum serum concentrations of T4 were obtained between 4-8 h. Serum Tg levels increased linearly with time during the first 24 h. Maximum serum Tg levels correlated well with basal serum Tg values (r = 0.97; P < 0.001). The maximal increment in Tg correlated inversely with the maximal increment in T3 (r = 0.71; P < 0.05). The half-life of Tg was estimated to be approximately 4 days by measuring the disappearance rate of Tg after its peak level was attained.