A New Method of Assay for Thyrotrophic Hormone

ADAMS and Purves (1953) have outlined a new method of assaying thyrotrophic hormone. The method is based upon the measurement of the action of the hormone in stimulating the secretion of thyroxine from the thyroids of guinea pigs. The measurement of the thyroxine released into the plasma is facilitated by labelling the iodine compounds of the thyroid with I131. Administration of thyroxine in amounts exceeding the normal demands of the animal inhibits the secretion of thyrotrophin from the animal’s own pituitary. In this paper the method is described in full, and some results obtained by use of the assay are reported. method (a) General Procedure Young guinea pigs, weighing 250–350 gm. are given twice-daily subcutaneous injections of 10 μg. L-thyroxine, these injections being continued until the conclusion of the assay. On the second day, each guinea pig is given 20 μc. carrier free I131 intraperitoneally.