Varying Effect of Thyroxine on Oxygen Consumption of Different Tissues.

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Abstract
Adult male albino rats were rendered hyperthyroid by subcut. injn. of thyroxine, 2.5-10 mg. every other day for 7-21 days. BMR of the animals showed a mean increase of + 116%. The respiration of tissue slices from normal and hyperthyroid animals was measured by the Warburg Method in 100% 02 at 37.5[degree] C in phosphate buffer and using glucose as substrate. Cerebral gray matter of hyperthyroid rats does not show the increase of respiration shown by the intact animal or by diaphragm muscle or kidney tissue. Liver tissue shows a highly variable respiration in hyperthyroidism, sometimes being abnormally low. These low-respiring tissues are, however, greatly stimulated by the addition of succinate. It would seem that in hyperthyroid liver there may be a shortage of co-enzyme for the glucose-pyruvate cycle. The cytochromeoxidase system, as judged by succinate response, remains intact or is enhanced.