Identification and characterization of a ouabain-like compound from human plasma

Area of Science:

• Biochemistry
• Physiology
• Pharmacology

Background:

• Animal cells possess sodium-potassium pumps regulating intracellular sodium.
• These pumps have high-affinity receptors for digitalis glycosides, suggesting an endogenous ligand.
• Previous research speculated the existence of an endogenous substance mimicking digitalis effects.

Purpose of the Study:

• To identify and characterize an endogenous ligand for the digitalis receptor.
• To investigate the physiological and pathological implications of this endogenous compound.

Main Methods:

• Purification of endogenous substance from human plasma.
• Structural identification using mass spectroscopy.
• Binding assays with [3H]ouabain.
• Enzyme inhibition assays for Na,K-ATPase activity.
• Measurement of 86Rb+ uptake.
• Detection of immunoreactive OLC in plasma and adrenal tissues.

Main Results:

• An endogenous substance indistinguishable from ouabain was purified from human plasma.
• This human ouabain-like compound (OLC) binds with high affinity to the digitalis receptor.
• OLC inhibits Na,K-ATPase and ouabain-sensitive 86Rb+ uptake, exhibiting cardiotonic actions.
• Immunoreactive OLC is present in mammalian plasma and concentrated in adrenals.
• Circulating OLC may influence intracellular sodium, calcium, and pH homeostasis.

Conclusions:

• An endogenous ouabain-like compound (OLC) exists in human plasma and acts on the sodium-potassium pump.
• OLC may regulate intracellular sodium balance and related physiological processes.
• Altered OLC levels could be implicated in the development of hypertension.