DIGOXINLIKE IMMUNOREACTIVE FACTOR ISOLATED FROM HUMAN PLEURAL FLUIDS IS STRUCTURALLY SIMILAR TO DIGOXIN

To further define the chemical structure of human endogenous digoxinli ke immunoreactive factors (DLIF) we used human pleural effusions as a source of the substance. Digoxinlike immunoreactive factor activity wa s detected by radioimmunoassay in the pleural fluid of each of four pa tients; average concentration was 0.35 ng/mL. The chemical profile of DLIF was determined by initial extraction and concentration of DLIF by ion exchange chromatography followed by reverse phase-high-pressure l iquid chromatography (RP-HPLC) separation and purification. Using high -pressure liquid chromatography cochromatography of DLIF, together wit h several radioactively marked glycosides, we observed a single peak o f DLIF activity that was chromatographically identical to digoxin, The present study further supports the recent finding that DLIF is relate d structurally to the cardiac glycosides, and for the first time it ha s been proven that DLIF is present in pleural fluids.