Natriuretic effect of atrial extract on isolated perfused rat kidney

To examine the mechanisms underlying the natriuretic action of a partially purified extract of rat atria (AE) we injected the equivalent of one atrium into isolated perfused rat kidneys. Some kidneys received an infusion of angiotensin II at 0.5 ng/min throughout the experiment. In the absence of angiotensin AE had a variable effect on renal vascular resistance (RVR) but, in the presence of angiotensin II, AE consistently decreased RVR by 3% for 5 min followed by a slight increase. Inulin clearance and filtration fraction increased slightly but significantly. AE increased sodium, chloride, phosphate, and free water clearance but not potassium excretion. Ventricular extract had no effect on any of these variables. Furosemide (50-250 micrograms) increased sodium, chloride, and potassium but not phosphate or free water excretion. AE did not alter dopamine or norepinephrine excretion. We conclude that AE increases the glomerular filtration rate (GFR) and inhibits tubular reabsorption by mechanisms which differ, at least in part, from those affected by furosemide.