COMPARISON OF THE METABOLIC EFFECTS OF DIFFERENT THYROID PREPARATIONS*

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Abstract
Rapid onset of increased nitrogen excretion following the daily administration of desiccated thyroid and diminution of the catabolic effect immediately upon cessation of therapy appeared inconsistent with the concept that this thyroid preparation is slow to act and prolonged in its effect. Consequently the effects of single, large, physiologically-comparable doses of triiodothyronine, thyroxine and desiccated thyroid were studied in 6 myxedematous and in 2 cuthyroid subjects. All 3 preparations were similar with regard to rapidity and duration of action, as judged by such indices of metabolic acceleration as nitrogen excretion, BMR, serum cholesterol level and pulse rate. In the patients with myxedema, identical clinical responses followed treatment with triiodothyronine and thyroid. The differences in response, as determined by the various indices of metabolic acceleration, were more pronounced between the subjects than between the compounds. Triiodothyronine induced a minimal rise in the serum PBI level, whereas desiccated thyroid induced a rise which was more consistent with other indices of metabolic acceleration. It is suggested that the calorigenic activity of desiccated thyroid is dependent on its content of, or rapid conversion to, triiodothyronine and thyroxine. Recent emphasis on the potency of triiodothyronine has engendered thebelief that its effects are strikingly different than those of desiccated thyroid and has encouraged the notion that it is a more effective therapeutic agent. The similarities between various thyroid compounds deserve equal stress.