Endogenous inotropic substance from heart tissue has digitalis-like properties

Area of Science:

• Cardiology
• Biochemistry
• Pharmacology

Background:

• Cardiac glycosides, like digoxin, are crucial for heart function.
• Endogenous digitalis-like substances (DLS) are implicated in cardiovascular regulation.
• Previous work established an extraction method for DLS from porcine ventricular tissue.

Purpose of the Study:

• To characterize a DLS isolated from porcine left ventricular tissue.
• To investigate the functional and biochemical properties of the purified DLS fraction.
• To determine the organic nature of the isolated DLS.

Main Methods:

• Extraction of crude DLS from porcine left ventricular tissue.
• Silica gel G column chromatography for fraction purification.
• Assays for inotropic activity on canine trabeculae.
• Measurement of ouabain-sensitive 86Rb+ uptake in rat heart slices.
• Enzyme inhibition assays using canine kidney Na+, K(+)-ATPase.

Main Results:

• The crude fraction cross-reacted with digoxin antibodies, showing 4.25 +/- 0.6 ng/ml digoxin equivalent.
• Purified fraction C demonstrated potent positive inotropic effects.
• Fraction C dose-dependently inhibited ouabain-sensitive 86Rb+ uptake (50% inhibition at 25 µl).
• Fraction C inhibited Na+, K(+)-ATPase activity (50% inhibition at 17 µl).
• Ashing fraction C at 500°C abolished its activity, confirming an organic origin.

Conclusions:

• A purified fraction (C) containing an endogenous DLS was isolated from porcine heart.
• This DLS exhibits cardiac glycoside-like properties, including positive inotropy and Na+, K(+)-ATPase inhibition.
• The findings support the role of endogenous DLS in cardiac function and suggest potential therapeutic applications.