Failure of atrial myocardial extract to inhibit renal Na+, K+-ATPase

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 less than 30,000) of boiled extract of rat atria and ventricles were prepared. Infusion of 100 microliters of the atrial ultrafiltrate into bioassay rats resulted in a prompt, short-lived natriuresis and diuresis. However, addition of 100 microliters of the atrial ultrafiltrate to 900 microliters 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.