Abstract
The interesting observation that turtle or alligator thyroid had practically no effect on the basal metabolic rate of man was made by Swingle and Martin. 1 The iodine content of the thyroid preparations fed was very high, over 4 mg per g, and so, by mammalian standards, these glands should have been fully iodized and resting, with alveoli filled with dense colloid. Such thyroids have always been found to have strong physiological activity. In contrast to the action of these preparations on man, when they were given to rabbits, the metabolic rate was raised to about the same extent as when cattle thyroid was fed. Swingle and Martin attribute the different behavior of reptilian thyroid in man and the rabbit to the fact that the dose used for rabbits was relatively large.
Since this work was reported, methods for the accurate estimation of thyroxine in thyroid have been developed and these were applied to various samples of reptile thyroid, including those used by Swingle and Martin, to determine whether the distribution of iodine differed from that found in mammalian thyroid. As a check on the validity of the analyses, the metamorphosing action of these preparations of tadpoles was studied and compared with the action of several dogs' thyroids.
Methods. Thyroxin was measured by Blau's 2 modification of the Leland and Foster 3 method. In addition to the dried alligator and turtle thyroids used by Swingle and Martin, samples of which had been in this laboratory since Marine determined their influence on rabbit metabolism in 1926, we obtained thyroids of 4 Caribbean Sea turtles. These animals weighed between 70 and 110 kg and had been kept in a warm room on their backs for about 10 days before they were killed.
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