Effect of methylxanthines on binding of L-triiodothyronine (T3) to cytosolic and nuclear extract receptors of human leukocytes.

The effect of 15 mM methylxanthines (theophylline, coffeine) and 15 mM papaverine on T3 binding in the cytosol or nuclear extract receptors of human leukocytes was investigated by charcoal-dextran assay. In the cytosol, the presence of all three compounds increases the apparent association constants (KA) without affecting the total number of binding sites (N). Binding capacity was practically the same, only coffeine slightly decreases the number of binding sites. In the nuclear extract receptor protein, only theophylline increases its apparent affinity for T3.