Analogous effects of serum lipids from patients with nonthyroidal illness and normal subjects on the uptake of thyroxine and its conversion to triiodothyronine by rat hepatocytes in culture.

The low level of triiodothyronine (T3) in nonthyroidal illnesses (NTI) has been attributed to the decreased peripheral conversion of thyroxine (T4) to T3; patient's serum lipids decreased the conversion in a cell-free system. The objective of our study was to determine whether patients' serum lipids, whose content was elevated 2.5-fold above the reference serum value, and oleic acid affected the uptake of T4 and its conversion to T3 by rat hepatocytes in culture, thereby providing information on the cell's response to these processes. Serum ether extracts and oleic acid (0.1 mumol/l) were incubated with cells followed by assessment of T4 uptake and conversion of T4 to T3. The mean T4 uptake in the presence of ether extracts of NTI patients' or normals' sera were similar (112 +/- 15% and 110 +/- 24%, respectively). There was no difference in the T4 to T3 conversion between the patient and normal groups (90 +/- 14%); oleic acid also did not influence the conversion (96.7 +/- 1.6%). Uptake and conversion in the absence of either extracts and oleic acid were controls. These results suggest that serum lipids from NTI patients and normal subjects exercise qualitatively and quantitatively almost similar influences on T4 uptake and its conversion to T3; oleic acid is not an inhibitor of T4 uptake and T4 to T3 conversion in the rat hepatocyte. Since hepatocytes actively process fatty acids, their influence on intracellular conversion of T4 is not equitable with T4 conversion using the cell-free system. Our results do not support the hypothesis that abnormal lipid metabolism in NTI impairs hepatic T4 to T3 conversion.