Failure of Atrial Myocardial Extract to Inhibit Renal Na+, K+-ATPase

Abstract

The effects of a natriuretic factor contained in extracts of the atrial myocardium on an isolated renal Na⁺, K+-ATPase enzyme system were evaluated. Ultrafiltrates (molecular weight < 30,000) of boiled extract of rat atria and ventricles were prepared. Infusion of 100 µl of the atrial ultrafiltrate into bioassay rats resulted in a prompt, short-lived natriuresis and diuresis. However, addition of 100 µl of the atrial ultrafiltrate to 900 µl of a suspension containing Na⁺, K⁺-ATPase had no significant effect on enzymatic activity. Similarly, ultrafiltrates of ventricular extract also had no significant effect on Na⁺, K⁺-ATPase activity. These results indicate that the atrial natriuretic factor does not alter renal tubular sodium reabsorption by directly inhibiting the Na⁺, K⁺-ATPase enzyme system.