Assessment of the degradation of thyroid hormones in man during bed rest

The effect of bed rest on the absolute turnover rates of thyroid hormones, thyroxine (T4) and triiodothyronine (T3), was evaluated in man. Bed rest resulted in physical deconditioning, measured by a decreased rate of maximal oxygen consumption; physical deconditioning was associated with no significant alterations in the metabolic clearance of T4 and T3. Plasma concentrations of these iodothyronines were not changed as a result of bed rest. Absolute hormone turnover rates were similar in control and bed-rest subjects. The data suggest that the degradation of thyroid hormones is not influenced by physical deconditioning or hypodynamia.