THE physiologic basis for the agreement between the clinical effectiveness of various thyroid preparations and their potency as assayed by the u.s.P. total iodine method has been well reviewed by Means (1). From assays in myxedematous patients, Salter, Lerman and Means (2, 3) concluded that the calorigenic activity of thyroid is related to its total organic iodine and not to its thyroxine iodine. In all of their assays of desiccated thyroid the response was four or five times greater than expected on the basis of its thyroxine content. Assays in rats by Gaddum (4) and Frieden et al. (5, 6), in guinea pigs by White, McGinty, Anderson and White (7), and in amphibia by Hamilton, Albert and Power (8) showed similar results. These investigators observed that natural thyroid proteins show more thyroxine-like activity than can be accounted for from their thyroxine content, even assuming that dZ-thyroxine possesses half the activity of Z-thyroxine. With this assumption other investigators reported agreement between the activities of thyroid preparations and dZ-thyroxine in terms of Z-thyroxine content (9, 10). On the other hand, evidence that the activity of thyroid proteins may not be correlated with either total iodine or thyroxine.content was reported by Meyer and Wertz (11).
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Kroc et al. (1954) studied this question.