Role of atrial natriuretic factor in the natriuresis of acute volume expansion.

The quantitative role of atrial natriuretic factor (ANF) in mediating the natriuresis induced by acute volume loading was determined in these studies. Plasma level of ANF (PANF), glomerular filtration rate (GFR), and renal excretory responses were measured in three groups of anesthetized Sprague-Dawley rats. In one group of rats (n = 8), acute volume expansion was established by intravenous infusion of saline (5% body wt) over a period of 30 min. A second group of rats (n = 13) was infused with synthetic ANF (2 micrograms X kg-1 X h-1 iv) to mimic the high PANF observed during acute volume loading. A third group (n = 13) served as control. PANF was similar and significantly elevated (P less than 0.05) in volume-expanded and ANF-infused groups compared with control. In control rats, PANF measured 122.0 +/- 12.1 pg/ml, whereas it averaged 389.4 +/- 30.3 pg/ml for volume-expanded and 368.1 +/- 22.3 pg/ml for ANF-infused rats. GFR was also comparable and significantly increased (P less than 0.05) in volume-expanded and ANF-infused groups compared with control rats. Infusion of ANF at a dose to mimic PANF obtained during acute volume expansion resulted in a fourfold increase in the fractional excretion of sodium. The results of these studies suggest that ANF may play an important quantitative role in promoting natriuresis during acute volume expansion.