METABOLISM OF RADIO-IODINE IN THE THYROIDS OF RATS EXPOSED TO HIGH OR LOW TEMPERATURES

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Abstract
The thyroid glands were examined in rats exposed to cold (0[degree]-2[degree]C) or heat (32[degree]-34[degree]C) for various lengths of time, using histological criteria and radio-iodine uptakes as tests of the activity of the glands. In the cold, the thyroid stimulation was doubtful after 1-3 days, definite after 7 days, maximal at 26 days, but absent after exposure for 40 days. At the time of maximal stimulation by the cold, the fixation of radio-iodine by the glands is 2.7 times that in the controls. Separation of the I fractions of the thyroid glands at various time intervals indicates that the turnover of thyroxine and the excretion of iodized products are increased to about twice the normal rates. Exposure of rats to heat lessens thyroid activity. This decrease can be observed as early as one day after the beginning of the exposure and persists for at least 26 days. It is slight, whether I fixation, thyroxine turnover, or excretion of iodized products are considered.