Effects of Thyroxine, Thyroidectomy and Lowered Environmental Temperature on Incorporation of Deuterium into Cholesterol.

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Abstract
The incorporation of deuterium (D) administered as D2O in H2O into cholesterol was studied in normal rats, in rats injected with thyroxin, and in thyroidectomized rats. D content of the cholesterol isolated from the liver was significantly greater in the hyperthyroid rats, and significantly lower in the thyroidectomized animals, than in the control group. The values for the intestine, kidneys and spleen showed a similar trend. Thyroid hormone probably stimulated the incorporation of D into cholesterol. In further expts. the same phenomenon was compared in thyroidectomized rats kept at room temp. and at 2-5[degree]C. No difference was found in the D uptake of the liver cholesterol of these 2 groups, although the lower environmental temp. is known to cause a significant increase in the metabolic rate even in the absence of the thyroid gland. The incorporation of D into cholesterol was probably specifically related to the concn. of circulating thyroid hormone, and not to the metabolic rate in general.