THE EARLY METABOLIC EFFECTS OF DESICCATED THYROID, THYROXINE AND TRIIODOTHYRONINE IN MAN: COMPARISON WITH EARLY EFFECT OF THYROTROPIC HORMONE

In order to determine whether the early metabolic effect of thyrotropic hormone (as demonstrated previously in this laboratory) could be reproduced by certain known thyroid hormone preparations, triiodothyronine (T3), thyroxine (T4) and desiccated thyroid were administered orally on four occasions in single doses to 5 normal males, and the metabolic effects observed. The dose of T3 was 0.5 mg.; of T4 2.5–3.0 mg.; and of thyroid, 1.3–2.0 Gm. Observations were made over an eight-hour period after an overnight fast. It was confirmed that T3 produces a rise in metabolic rate and an increase in the levels of plasma and urinary phosphate within eight hours without significantly raising the level of plasma protein-bound iodine (PBI). There was a less marked rise in metabolic rate following administration of desiccated thyroid, with a significant rise in urinary phosphate within eight hours and a rise in the plasma PBI level to 10.2 μg. per 100 ml. within two hours. T4 produced no elevation in metabolic rate, pulse rate or phosphate excretion, although elevation of the plasma PBI level to 9.0 μg. per 100 ml. occurred within two hours. There were no consistent effects on urine flow and sodium, potassium or creatinine excretion, and no subjective symptoms during treatment with any of the preparations. The results indicate the similarity between the early metabolic effects of triiodothyronine and desiccated thyroid. Thyroxine had no effect over the eight-hour period of observation. None of the preparations reproduced the early metabolic effects of thyrotropic hormone.