On the Competitive Interaction of Long-Acting Thyroid Stimulator and Thyrotropinin Vivo1

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Abstract
We have previously demonstrated (2) that thyrotropin (TSH) “protects” the longacting thyroid stimulator (LATS) from inhibition by thyroid microsomes, suggesting that LATS and TSH act at the same site(s) in the thyroid gland. In order to confirm this postulate, we performed experiments to determine if bioassay response to LATS was modified by prior administration of TSH and/or if the converse obtained. The results indicate that TSH given 1–2 hr prior to or concomitant with the administration of LATS results in significant decrease in murine thyroidal response to the latter stimulator. LATS-IgG given 2 hr before 0.8 mU TSH almost completely prevented response (131I release) to the latter despite control mice that exhibited a greater total response to larger doses of either agent. Although these data indicate an action of these stimulators at the same thyroidal site(s) and suggest that the TSH and LATS molecules may have similar thyroid-stimulating groupings, alternate possibilities are not excluded. It is concluded that present information regarding the mode of action of TSH and/or LATS is insufficient to permit definitive interpretation of their competitive interaction in vivo.

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