• H Eiskjaer, C B Nielsen, S S Sørensen, and E B Pedersen.
• Department of Medicine and Nephrology C, Skejby Hospital, University Hospital, Arhus, Denmark.
• Eur. J. Clin. Invest. 1996 Jul 1; 26 (7): 584-95.

AbstractIn order to study the renal and hormonal actions of atrial natriuretic peptide (ANP) during background infusions with angiotensin II (ANG II) or noradrenaline (NA), 69 healthy subjects were examined in three main groups receiving a 90-min infusion with either placebo, ANG II (1.5 ng kg-1 min-1), or NA (25 ng kg-1 min-1). Each of these three main groups were subdivided into two groups receiving an infusion with either placebo or ANP (10 ng kg-1 min-1) for the last 60 min of the background infusion. Lithium clearance was used to evaluate segmental tubular reabsorption. ANG II alone caused a decrease in glomerular filtration rate (GFR), renal plasma flow, urinary absolute and fractional excretion of sodium, both proximal and distal fractional tubular sodium reabsorption, and urinary flow. NA alone caused a decrease in renal plasma flow. ANP alone caused a decrease in renal plasma flow. Urinary absolute and fractional excretion of sodium were increased and the distal fractional tubular reabsorption of sodium decreased, whereas the proximal fractional tubular reabsorption was unchanged by ANP. ANG II + ANP: during a background ANG II infusion, ANP still increased fractional excretion of sodium. Proximal fractional reabsorption was decreased, whereas distal fractional reabsorption of sodium was unchanged by ANP during ANG II infusion. The ANP-induced decreases in proximal absolute (-147 vs. +714 mumol min-1 1.73 m-2, P = 0.05) and fractional (-1.7% vs. +0.6%, P < 0.01) tubular sodium reabsorption were more pronounced, and the decrease in distal fractional tubular reabsorption of sodium (-0.1% vs -1.4%, P < 0.05) less pronounced compared with when ANP was given alone. NA + ANP: during a background NA infusion, ANP still increased urinary sodium excretion and decreased distal fractional reabsorption. None of the ANP-induced absolute changes seen during background infusion with NA were significantly different from the ANP-induced changes seen during placebo background infusion. It is concluded that the natriuretic action of low-dose ANP seems to be preserved during background infusions with ANG II and NA in man. Net sodium excretion during the combined infusion with ANG II and ANP seems to reflect the sum of the opposing influences of each peptide. Low-dose ANP had a very modest but significant inhibitory effect on proximal tubular sodium reabsorption prestimulated by ANG II infusion.

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