Digoxin immunoreactivity in cord and maternal serum and placental extracts. Partial characterization of immunoreactive substances by high-performance liquid chromatography and inhibition of Na+, K+-ATPase.

Digoxin-like immunoreactive substances (DLIS) have been successfully extracted and concentrated from cord serum, mixed (cord and maternal) serum and placentas. Similar substances have also been extracted from normal adult serum, but DLIS in this medium are present in much lower concentrations. Concentrated DLIS have been separated into several immunoreactive fractions by use of reverse-phase high-performance liquid chromatography. Immunoreactive fractions were tested for their ability to inhibit the Na+,K+-ATPase by measuring the 86Rb-uptake of red blood cells in the presence of these fractions. A potent inhibitor was identified in an immunoreactive fraction which also contains progesterone, but the results suggest that the pump inhibitor is not progesterone. Cross-reactivity studies utilising fluorescence polarization immunoassay have shown that cortisone is the most potent immunoreactive substance of cord serum.