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1 Department of Pharmacology, University of Toronto
Two methods to measure thyroid activity are described and compared with other bioassays of this hormone.
One is a quantal response type of assay depending upon the decreased resistance to anoxia of mice treated with thyroxine. The slope (b) for this procedure was 3.53 ±0.76.
The other is a graded response method based on the acute weight loss of rats during the 48 hours following the first of two injections of thyroxine. The standard deviation of this method was 4.4 and the slope of the log dose response curve was 9.1. The value for 
was, therefore, 0.478.
The acute, transient loss of weight is apparently due to a reduction of the water and food intake by the animals. It is not produced by injections of diiodotyrosine. Rats previously treated with thiouracil have a greater transient weight loss after the administration of thyroxine than have normal rats.
Submitted on July 30, 1948
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