Identification of 11,13-dihydroxy-14-octadecaenoic acid as a circulating Na⁺/K⁺-ATPase inhibitor

Two digitalis-like compounds (DLC) were purified to homogeneity from bovine plasma. The purification procedure consisted of organic extractions and batch chromatography followed by three subsequent separations using reverse-phase high-performance liquid chromatography. The presence of a DLC in the different fractions was monitored by their ability to inhibit (a) [³H]ouabain binding to rat brain synaptosomes, and (b) microsomal Na⁺/K⁺-ATPase activity. Using mass spectrometry and nuclear magnetic resonance spectroscopy the structure of one of the DLCs was identified as 11,13-dihydroxy-14-octadecaenoic acid. It is suggested that this new hydroxy, unsaturated, fatty acid derivative may regulate Na⁺/K⁺-ATPase activity under some physiological and pathological conditions.