1. 125I-labelled c-atrial natriuretic peptide-(4–23) was used as radioligand for the direct quantification of atrial natriuretic peptide clearance receptors, and 125I-labelled rat atrial natriuretic peptide-(1–28) was used for the determination of total and biologically active atrial natriuretic peptide receptors, in renal glomerular and papillary membrane preparations of chronically salt-loaded and control rats.
2. The membrane preparation technique included acid-washing (pH 5), and receptor binding was assessed by saturation studies at 4°C for 3 h. Chronic salt loading revealed a 35% decrease in clearance receptor number in the glomerular membrane and a 42% decrease in the papillary membranes. The absolute decrease in clearance receptor number was almost identical with the observed reduction in absolute number of total atrial natriuretic peptide receptors. Biologically active receptors were not affected by chronic salt loading.
3. Selective downregulation of clearance receptors for atrial natriuretic peptide may reflect an important role for the rat renal atrial natriuretic peptide system in long-term fluid and electrolyte regulation.