Comparison of Alterations in Circulating Thyroglobulin, Triiodothyronine and Thyroxine in Response to Exogenous (Bovine) and Endogenous (Human) Thyrotropin
The effects of exogenous bovine and endogenous thyrotropin (TSH) on human thyroglobulin (Tg), triiodothyronine (T3) and thyroxine (T4) concentrations in serum were studied. Serum Tg, T3 and T4 concentrations were determined in the same sera by use of a radioimmunoassay specific for each of the 3 thyroidal products. In 5 normal subjects given 10 IU of bovine TSH, the mean peak serum T3, T4 and Tg concentrations were reached at 8, 24 and 48 hr, respectively, after injection. The maximal increase above baseline was 94% for T3 93% for T4 and 474% for Tg. Eight normal subjects were given 200 μg of synthetic TRH iv as a bolus injection. They responded with an increase in serum TSH concentration from a mean baseline value of 3 and T4 levels all occurred at 4 hr after TRH injection, with a mean increase above basal value of 47%, 70% and 34%, respectively. The possible mechanisms for the observed differences in serum Tg, T3 and T4 response to exogenous (bovine) TSH and endogenous (human) TSH are presented in the discussion.