REDUCED RENAL EXTRACTION OF ATRIAL-NATRIURETIC-PEPTIDE IN PRIMARY ALDOSTERONISM

We investigated renal and peripheral forearm extraction of atrial natr iuretic peptide in patients with primary aldosteronism to determine wh ether alterations in extraction may contribute to the elevated levels of circulating atrial natriuretic peptide observed in primary aldoster onism. We obtained simultaneous venous blood samples from the left ren al vein and a peripheral vein and from the radial artery in 28 patient s with primary aldosteronism and 10 patients with essential hypertensi on. Renal extraction of atrial natriuretic peptide was significantly ( P<.001) reduced (40+/-2%) in primary aldosteronism compared with essen tial hypertensive patients (62+/-3%). Peripheral forearm extraction wa s also reduced (P<.01) in primary aldosteronism compared with essentia l hypertensive patients (24+/-3% versus 38+/-4%). These findings are c onsistent with widespread downregulation of atrial natriuretic peptide receptors in primary aldosteronism. Consistent with reports that mark ed reduction in glomerular filtration rate is required before the rena l extraction of atrial natriuretic peptide is reduced, no significant relationship between renal extraction of atrial natriuretic peptide an d plasma creatinine was seen in primary aldosteronism or essential hyp ertension. Although the major regulators of atrial natriuretic peptide secretion in primary aldosteronism are presumably alterations in arte rial blood pressure and plasma volume, reduced renal and peripheral ex traction of atrial natriuretic peptide in primary aldosteronism may al so contribute significantly to the elevated circulating levels observe d.