Effect of synthetic atrial natriuretic factor on superficial and deep proximal tubule sodium reabsorption

The effects of synthetic atrial natriuretic factor (ANF) on sodium reabsorption by deep and superficial proximal tubules were examined in the rat. In response to ANF infusion (4 micrograms/kg/hr), the urinary fractional excretion of sodium increased from 1.21% +/- 0.53% to 3.48% +/- 0.48%, p less than 0.05 (n = 12). Fractional delivery of sodium (FDNa) from the deep proximal tubule was 25.9% +/- 3.7% before and 33.7% +/- 3.4% after ANF infusion. In time control animals, FDNa from deep proximal tubules was 34.3% +/- 3.0% and 28.5% +/- 4.0% respectively (n = 12). The change in FDNa from deep proximal tubules during ANF infusion (increase of 7.8% +/- 3.9%) was significantly different from the change in control animals (decrease of 5.8% +/- 3.1%) (ANF infusion vs control, delta 13.7% +/- 4.9%, p less than 0.05). No significant change was observed in FDNa in the superficial proximal tubule either during ANF infusion or in control animals. In summary, ANF infusion increased urinary fractional sodium excretion; however, fractional sodium reabsorption by the proximal tubule of superficial nephrons was unchanged. In contrast, sodium delivery to the point of micropuncture in the descending limb of Henle's loop of deep nephrons was increased, as compared with controls, suggesting inhibition of sodium reabsorption by proximal tubules of deep nephrons.