Bestimmung der Eiweißbindung verschiedener Herzglykoside mittels Sephadex^®-Gelfiltration

Summary

The binding of tritium labelled cardiac glycosides to plasma proteins was investigated by means of the Sephadex gel-filtration method. After pre-saturation with water, Sephadex G 25 was incubated with an excess of guinea pig plasma which contained ³H-labelled heart glycosides. In this procedure, the Sephadex G 25 could not disturb the equilibrium between the free and protein-bound glycoside to a noticeable extent. The uptake of ³H-glycosides by Sephadex from serum was compared with that from a TRIS-buffered 0.9% NaCl-solution containing the drug in the same concentration as the serum or plasma. From the ratio of both values the amount of protein-bound glycoside could be calculated. Approximately 90% of the ³H-digitoxin incubated with guinea pig plasma or with human serum became bound to protein; for ³H-digoxin, this figure was about 55%. No significant protein binding could be established for ³H-ouabain, neither in guinea pig plasma nor in human serum. In contrast to previous investigators, who used toxic concentrations of the glycosides, the present studies have been carried out with glycoside concentrations within the therapeutic range. The results have been compared with those of previous authors.