EFFECT OF HEPARIN ON SERUM FREE THYROXINE LINKED TO POST-HEPARIN LIPOLYTIC ACTIVITY

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Abstract
A possible association between free thyroxine (fT4) changes, occuring after heparin administration, and the post-heparin lipolytic activity, i.e., the release of lipases and the lipolysis of triglycerides to non-esterified fatty acids (NEFA) was studied. In 19 patients heparin increased mean fT4 values obtained by equilibrium dialysis from 23.4 to 38.6 pmol/l (P < 0.01) and mean fT4 values measured by GammaCoat 2-step radioimmunoassay from 17.0 to 24.1 pmol/l (P < 0.01), the results of the 2 methods agreeing well (rS = 0.88). Concurrently, NEFA increased from a mean of 0.55 to 2.20 mmol/l (P < 0.01) and fT4 increases were significantly correlated with post-heparin NEFA (rs = 0.69, P < 0.001). In vitro addition of palmitic acid to sera increased fT4 concentrations to values similar to those observed in vivo. Post-heparin fT4 increases were also strongly correlated to the concentrations of triglycerides (rs = 0.63, P < 0.01). Hypertriglyceridemia was associated with pronounced fT4 increases after heparin administration, and normolipidemia with moderate or no changes. The effect of heparin on fT4 apparently is linked to the activation of lipases by heparin and is mediated by NEFA, which, at high concentrations, compete with T4 for binding proteins.