Metabolic Rate Changes Following Thyroid Destruction by AT 211 and I 131 in the Rat

Abstract

Summary

(1) The time course of the development of hypothyroidism in rats, as judged by the animals' metabolic rates, following the administration of thyroidectomizing doses of At²¹¹ and I¹³¹ has been studied. (2) The metabolic rate decreased abruptly to 74% of the control value between 6 and 8 days after the administration of 0.8 μc of At²¹¹ per g of body weight. A further decrease to the subsequent steady value (between 65% and 70% of the corresponding values for the control group) had occurred by about 20 days from the date of injection. (3) Slowing of the metabolic rate was first observed between 8 and 12 days after the administration of I¹³¹ (10 μC per g of body weight). The metabolic rate decreased more slowly in the I¹³¹-treated than in the At²¹¹-treated animals, but ultimately attained a similar steady value(4). It is suggested that the differences which have been observed after the administration of At²¹¹ and I¹³¹ may be correlated with the different nuclear properties of the 2 isotopes.