3,3',5'-triiodothyronine (reverse T3) in human cerebrospinal fluid.

Abstract

To examine the metabolic products of thyroid hormones in the central nervous system, total and free rT3 as well as T4 in human cerebrospinal fluid (CSF) were determined in 41 patients. Total T4, T3, and rT3 concentrations in CSF were determined by RIA, and free T4, T3, and rT3 fractions were analyzed by the magnesium precipitation method. The mean (+/- SE) total T4 and T3 concentrations in CSF were 166 +/- 24 and 2.6 +/- 1.5 ng/dl, respectively; the values were approximatey 2% of those in normal control pooled sera. Total rT3 concentrations in CSF from 29 clinically euthyroid patients who were apparently in a normal nutritional state ranged from 5.2-23 ng/dl (mean +/- SE, 11.2 +/- 0.9 ng/dl); the value was approximately 40% of that in sera. A patient with primary hypothyroidism had a markedly diminished CSF rT3 concentration (1.1 ng/dl), and the remaining 11 patients, suffering from severe diseases such as meningitis and cerebrovascular accident, had significantly higher CSF rT3 concentrations (37.5 +/- 6.6 ng/dl) than the clinically euthyroid patients. Although free T4 and T3 concentrations in CSF (5.9 +/- 1.1 and 0.16 +/- 0.05 ng/dl, respectively) were similar to those in serum (2.1 +/- 0.2 and 0.22 +/- 0.01 ng/dl, respectively), the free rT3 concentration in CSF (0.70 +/- 0.12 ng/dl) was approximately 20 times higher than that (0.044 +/- 0.016 ng/dl) in serum. Furthermore, the reciprocal relationship was observed between CSF total rT3 concentrations and free rT3 percentages in CSF. These data suggest the possibility that rT3 may be produced from T4 in human brain and that there may be a transport mechanism regulating free rT3 in CSF.