Importance of changes in plasmatic volume in the evaluation of TSH, L-T3 and L-T4, during muscular activity

The changes in plasma concentrations of TSH and thyroid hormones (L-T3 and L-T4), lactate, proteins and FFA were studied in 8 male volunteers undergoing maximal exercise during 12 min on the bicycle ergometer from 1 to 4 w/kg. Serial blood samples were taken at -30, 0, 3, 6, 9, 12, +3, +15 and +30 min intervals. All samples for TSH, L-T3 and L-T4 measurements were processed by radioimmunoassay. The possibility of interference in the RIA determination, with protein and FFA, has been studied in this work. However, in men the available evidence suggests that protein and FFA do not play an important role of interference in the determination methodology of thyroid hormone levels. This interpretation is in accordance with the fact that in men, plasma concentrations of thyroid hormones are related to changes in plasmatic volume, the intensity and the extended duration of the exercise.