Abstract
ABSTRACT Thyroid hormone content of cerebrospinal fluid (CSF) pooled from euthyroid patients was studied because of its possible relationship to brain T4 and T3 levels. The mean CSF total T4 level was 185 ng/100 ml, 1/40 the serum level, and the mean CSF T3 level was 17.4 ng/100 ml, 1/10 the serum level. Mean percent CSF free T4 was 3.5 and free T3 was 10.2. CSF absolute free T4 was 5.8 and absolute free T3 was 1.8 ng/100 ml, both exceeding the respective serum levels of 2.4 and 0.32 ng/100 ml. CSF TBPA bound 12.2% of T3 and 43.5% of T4, higher fractions than serum TBPA which bound 3.0% of T3 and 17.3% of T4. As estimated from maximum T4 binding capacities, the CSF TBG level was 13.2 ng/100 ml, 1/75 of the serum level, and the TBPA level was 1.47 mg/100 ml, 1/12 of the serum level. Although the total levels of T3 and T4 binding proteins were relatively small, thyroid hormone transport in CSF qualitatively resembled that in serum.
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