Fluid and electrolyte changes of thyroidectomized rats in a cold environment

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Abstract
Groups of adult male albino rats were thyroidectomized or sham-operated, and later subjected to 10 day, 5°C cold exposure or else maintained at 22°C room temperatures. Tissues were examined for total water, sodium, potassium, Na24 and I131-thyroxine distribution. Thyroidectomized animals in the cold showed significantly greater amounts of water and Na24 specific activity in muscle and brain. Sham-operated animals in the cold showed significantly reduced brain Na24 specific activity. Thyroxine I131/Na24 ratios in tissue were greater at room temperature in thyroidectomized animals and were decreased with cold. Sham-operated animals showed no differences in brain thyroxine I131/Na24 ratios after equilibration and small differences in muscle ratios, with cold. It was concluded that a cold environment imposed on thyroidectomized animals resulted in changes in the animal's capacity to readjust body fluids and electrolytes when compared with intact animals exposed to cold. These differences were attributable to greater tissue water content and increased sodium flux into the tissues.