Binding of Digitoxin and Digoxin to Normal Human β‐Lipoproteins

Abstract

Abstract The binding of digitoxin and digoxin to purified β‐lipoprotein, obtained from pooled normal human serum, was studied under equilibrium conditions. Even with as high concentrations of unbound digitoxin or digoxin as 4 μmol/1 the preparations of β‐lipoproteins, containing cholesterol 1.98–3.95 mmol/1, did not show any signs of saturation. The binding affinity of digitoxin was about ten times as high as that of digoxin. Gel filtration chromatography, performed on native serum after addition of 3H‐digitoxin or 3H‐digoxin, showed a minor fraction of the cardiac glycosides to be associated with the protein fraction of highest molecular weight. This phenomenon disappeared after precipitation of the β‐lipoproteins. In clinical relations the contribution of protein bound digitoxin caused by the lipoprotein interaction is immaterial, in relation to that caused by the albumin interaction.