Recent evidence suggests the existence of several endogenous Na+,K+-
ATPase inhibitors in mammals. Previously, we have shown that the amphibian
Na+,K+-ATPase inhibitor marinobufagenin (3,5-dihydroxy-14,15-epoxy bufodienolide) acts as a
vasoconstrictor in isolated rat and human arteries. Mammalian plasma was shown to contain
marinobufagenin-like immunoreactive material, which is responsive to saline volume expansion. The present study describes purification of a bufodienolide, which is similar to
marinobufagenin, from the urine of patients after acute
myocardial infarction with the use of thin-layer chromatography and reverse-phase high-performance liquid chromatography (HPLC). The purified substance cross-reacted with
marinobufagenin antibody, demonstrated maximal UV absorbance at 300 nm characteristic of bufodienolides, and eluted from HPLC columns with the same retention time as
marinobufagenin. Mass spectrometry of purified material revealed the presence of a substance indistinguishable from amphibian
marinobufagenin and having molecular mass of 400 D. The present studies show that one of the human
digitalis-like factors may have a bufodienolide structure and is likely to represent
marinobufagenin or its isomer, and they suggest a role for this substance in the pathogenesis of
myocardial ischemia.