[Changes in the activity of the thyroid gland in polar foxes as a function of age and varying temperatures of the...

Investigations were carried out concerning the thyroid activity in 76 adult and 15 young (2 1/2 months old) polar foxes by means of the J131 test. The criteria for determining the thyroid activity were as follows: the rate of J131 excretion in the urine and faeoes, protein-bound J131 in blood plasma (PBJ131), conversion index, and the two hours' test on the uptake of radioactive iodine by the thyroid in the animals tested. The thyroid activity in the young foxes was found to be twice as high on the average as that in the adult animals. Significant differences in the thyroid activity were observed in animals kept under different temperature conditions. The rate of radioactive iodine uptake and of the thyroid hormone synthesis, as well as the rate of the appearance of hormone iodine in blood were higher in the animals kept al lower temperatures. It was found that a higher level of PBJ131 and WKJ131 resulted i lower rate of J131 excretion in the urine and faeces.