Inter-relationship of iodine-131 uptake by thyroid gland and CO2 production with metabolic body weight in sheep

Uptake of iodine-131 by thyroid gland was studied in 10 adult sheep of 28.2 kg average body weight. A single dose of 131I(20μCi) was injected subcutaneously on the medial side of thigh. Maximum uptake of labelled iodine ranging from 6-12 percent was observed between 72-96 h after injection. Carbon dioxide production rate was studied in the blood of the same sheep. Labelled sodium bicarbonate (NaH14CO3) was injected continuously through jugular vein at a rate of 200 mμCi/min. Plateau in the specific radio-activity was obtained after 3 h. The average CO2 production rate was 143.5 +- 21.7 ml/min. Carbon dioxide production rate was not found to be affected by the level of radio-iodine uptake. Significant relationship of metabolic body weight was obtained with CO2 production rate, but no such relationship was found with iodine uptake. (author)