A rapid and potent natriuretic response to intravenous injection of atrial myocardial extract in rats.

Supernatants of atrial or ventricular myocardial homogenates were injected intravenously into anesthetized non-diuretic rats. Extract derived from atrial muscle caused a rapid, more than 30-fold increase of sodium and chloride excretions, while urine volume rose 10-fold, and potassium excretion doubled. No such changes were observed after injection of ventricular tissue extract obtained from the same rat hearts, or after injection of the homogenization medium. There was no significant difference in glomerular filtration rates between the two groups. We conclude that the atrial extract contained an extremely powerful inhibitor of renal tubular NaCl reabsorption.