Abstract
Of the several methods employed in assays of thyrotropic hormone that utilizing the structure and weight responses of the thyroids of guinea pigs is the most commonly used. 1 2 Day-old white leghorn chicks have been found not only to respond more sensitively than guinea pigs but also to give a relatively greater weight increase and to exhibit a more uniform thyroid structure.
The preparation used was a partially purified alkaline extract of beef anterior pituitary. 3 Although a response is elicited by a single dose in 24 hours, 5 daily injections were found to give a maximal reaction. Further division of doses into 2 a day for 5 days gave a somewhat greater response.
One hundred and seventy-five injected chicks and 36 uninjected controls furnish the basis for the assay curve. Each sample of extract was tested on 5 chicks. At autopsy the thyroids, dissected under a binocular microscope, were weighed and body weight and sex recorded. The total dose was divided into 5 daily subcutaneous injections. It was found advisable to do the autopsy 24 hours after the last injection. Table I gives a representative series of the mean thyroid weights and total dose of extract used. Most dosages were repeated on different hatchings, with separate batches of extract. Total doses varied from 0.1 to 20.0 mg. Increases in thyroid weight were produced by increased dosages up to 10.0 mg. but beyond this there was no further increase in thyroid weight. Thus, a maximum thyroid weight is produced with 100 times the minimum stimulating dose. The larger doses produced thyroids averaging 6 to 7 times the mean weights of controls.
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