This chapter presents two methods—(1) T4 to T3 Conversion in the rat and (2) T4 to T3 conversion in human subjects. The conversion of T4 to T3 in the rat is determined by measuring the rate of change of radioactive T3 in the whole animal after the injection of tracer T4. The rate of change of tracer T3 in the body is equivalent to the net effect of conversion of T4 to T3 and the irreversible metabolism of the T3 that is generated. In human beings, the fractional rate of conversion of T4 to T3 is determined by measuring simultaneously the turnover rates of T4 and T3 in subjects without endogenous thyroid function who are maintained in the euthyroid state by treatment with synthetic L-thyroxine. As the only source of T3 in these subjects is from the metabolism of the administered T4, the T3 turnover is equivalent to T3 converted from T4.
ASJC Scopus subject areas
- Molecular Biology