Localization of atrial natriuretic peptide binding sites within the rat kidney

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Abstract
Although synthetic atrial natriuretic peptides (ANP) have potent natriuretic/diuretic properties, the renal mechanisms underlying these effects are not yet clearly defined. To determine the possible sites of action for ANP within the kidney, we have localized 125I-ANP binding sites by in vitro autoradiography. Slices of rat kidney were incubated with 150 pM 125I-ANP [alpha-rat ANP (alpha-rANP), 28 amino acids] alone or in the presence of 10 nM or 1 microM unlabeled ANP. Autoradiography was performed using LKB Ultrofilm or emulsion-coated cover slips together with histochemical/immunohistochemical staining of specific tubular segments. High-affinity 125I-ANP binding sites were concentrated over glomeruli and to a lesser extent over the arterial vasculature. Lower-affinity binding sites were seen over proximal tubules and inner medullary collecting ducts. The remainder of the nephron was unlabeled. The localization of high-affinity 125I-ANP binding sites in rat kidney is consistent with a glomerular filtration/hemodynamic mechanism as the principal means by which ANP promotes natriuresis/diuresis.