The renal action of atrial natriuretic peptide during control of glomerular filtration

Studies were performed in anesthetized dogs (N = 7) to determine the effects of synthetic atrial natriuretic peptide (ANP) on sodium excretion in the presence and absence of control of glomerular filtration rate produced by suprarenal aortic clamping. Intrarenal infusion of synthetic atrial natriuretic peptide (0.3 μg/kg/min) significantly increased glomerular filtration rate from 29.3 ± 3.0 to 43.2 ± 4.4 ml/min, urinary sodium excretion from 20.1 ± 10.3 to 223.3 ± 52.3 μEq/min, fractional sodium excretion from 0.47 ± 0.19 to 3.75 ± 0.59%. In contrast, aortic clamping blocked the increase in glomerular filtration rate in association with an attenuated natriuresis. Urinary sodium excretion increased from 6.3 ± 2.3 to 68.3 ± 23.4 μEq/min and fractional sodium excretion increased from 0.15 ± 0.04 to 0.90 ± 0.30%. Despite this differential response in glomerular filtration rate and sodium excretion, whole kidney fractional delivery of sodium from the proximal tubule as estimated by the fractional excretion of lithium increased during both unclamped (17.7 ± 1.8 to 30.4 ± 0.8%) and clamped (12.9 ± 2.1 to 23.9 ± 2.7%) periods. These studies demonstrate that atrial natriuretic peptide-induced natriuresis is importantly mediated by an increase in glomerular filtration rate and decrease in tubular reabsorption.