1. We studied the effect of a low-dose infusion of atrial natriuretic peptide (ANP) on renal blood flow in healthy volunteers. We additionally investigated the effect of ANP on renal haemodynamic function and on urinary sodium excretion.

2. ANP induced a rise in packed cell volume and a slight increase (but no decrease) in the renal extraction of hippuran. These changes did not offset the observed fall in effective renal plasma flow. Renal blood flow thus truly decreased and renal vascular resistance increased.

3. ANP induced an increase in glomerular filtration rate and a decrease in urinary osmolality in the first hour of ANP infusion, whereas absolute and fractional sodium excretion increased significantly only in the second hour of ANP infusion. The decrease in urinary osmolality in the first hour of ANP infusion correlated with the induced natriuresis. The changes in urinary osmolality and sodium excretion both correlated with the changes in plasma ANP levels.

4. These data indicate that ANP may cause a decrease in renal blood flow and an increase of renal vascular resistance in man. Our results suggest a role for ANP-induced (intra)renal haemodynamic changes in ANP-induced natriuresis, possibly through an increase in the filtered load of sodium into a washed-out medullary interstitium.

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