Acceleration of Thyroxine and Triiodothyronine Turnover During Bacterial Pulmonary Infections and Fever: Implications for the Functional State of the Thyroid During Stress and in Senescence
Thyroxine and triiodothyronine turnover have been studied in patients experiencing bacterial pulmonary infections, chiefly pneumococcal pneumonias. In 26 patients the acute phase of the illness was characterized by rapid thyroxine turnover (mean t½ 2.3 days ± 0.9, SD). With clinical recovery, turnover reverted abruptly to normal or, in some cases, slower than normal turnover rate (mean t½ 10.8 ± 2.0 days). Thyroxine distribution space was questionably reduced during the acute phase, but plasma hormone concentration (PBI and T4 by column chromatography) was the same during the acute and recovery phases. Calculated mean T4 disposal rate was 5-fold greater during the acute than during the recovery phase. Both old and young subjects showed these turnover changes in the 2 phases. Triiodothyronine turnover was measured concomitantly with T4 turnover in 6 patients and, like T4, showed acceleration during the acute phase (mean t½ 8.8 hr) with reversion to normal (t½ 33.7 hr) during recovery. In 7 additional patients no acceleration of turnover was seen during similar febrile illnesses. Since the plasma thyroxine concentration is maintained during a period of accelerated peripheral disposal, the data suggest acceleration of thyroidal thyroxine secretion during this type of stress. The data also support the concept that decreased thyroxine turnover under basal conditions in the elderly is secondary to an alteration in the mechanism(s) for hormone disposal and/or utilization rather than a decrease in the ability of the thyroid to secrete thyroxine.