Effect of thyroxin on assay of thyroid-stimulating hormone

¹ New York Agricultural Experiment Station, Cornell University, Ithaca, New York

The per cent colloid in the thyroid of the 3-day-old cockerel provides a sensitive measure of exogenous thyroid-stimulating hormone (TSH) potency. The smallest detectable dose of TSH is 0.5 mU; the log dose-response relation is linear between 5–500 mU of TSH, with a slope of –19.09 ± 0.90% colloid per unit log dose (mU) TSH, and an index of precision () of 0.21. The assay method shows good repeatability. Statistically, no interaction was detected in a 5 x 5 factorial experiment in which TSH was administered (5 times at 12-hr intervals in doses of 0, 3, 9, 27, or 81 mU) with dl-thyroxin (in doses of 0, 0.04, 0.16, 0.64, or 2.56 µg/injection). No TSH could be detected in the pituitaries of starved or fed 3-day-old cockerels when the equivalent of a total of five pituitaries per assay chick was administered.

Key Words: use of per cent colloid in chick thyroid for TSH bio-assay • TSH-thyroxin interaction

Submitted on March 7, 1963