Immunoreactive N-terminal Pro-Atrial Natriuretic Peptide in Human Plasma: Plasma Levels and Comparisons with α-Human Atrial Natriuretic Peptide in Normal Subjects, Patients with Essential Hypertension, Cardiac Transplant and Chronic Renal Failure

Plasma levels of immunoreactive N-terminal pro-atrial natriuretic peptide (N-terminal ANP) have been measured in 25 normal subjects, 29 patients with essential hypertension, six cardiac transplant recipients, seven patients with dialysis-independent chronic renal failure and 11 patients with haemodialysis-dependent chronic renal failure. Plasma was extracted on Sep-Pak cartridges and N-terminal ANP immunoreactivity was measured using an antibody directed against pro-ANP (1–30). 2. Plasma levels of TV-terminal ANP (means ± sem) were 235.3 ± 19.2 pg/ml in normal subjects and were significantly raised in patients with essential hypertension (363.6 ± 36.3 pg/ml), in cardiac transplant recipients (1240.0 ± 196.2 pg/ml), in patients with chronic renal failure not requiring dialysis (1636.6 ± 488.4 pg/ml) and patients with chronic renal failure on maintenance haemodialysis (10 336.1 ± 2043.7 pg/ml). 3. There were positive and significant correlations between the plasma levels of TV-terminal ANP and α-human ANP (α-hANP) with individual correlation coefficients of 0.68 within the normal subjects, 0.47 in patients with essential hypertension, 0.78 in patients with dialysis-independent chronic renal failure and 0.68 in patients with haemodialysis-dependent chronic renal failure (P < 0.05 in every case). 4. Gel filtration behaviour on Sephadex G-50 of the immunoreactive N-terminal ANP from Sep-Pak extracts of plasma from normal subjects or patients was consistent with a single peak having an elution volume corresponding to that of human pro-ANP (1–67) standard. 5. These studies demonstrate that the N-terminal pro-ANP peptide is co-secreted with α-hANP in both normal subjects and patients with cardiovascular/renal disease. The higher levels of the N-terminal ANP may reflect differences in the rate of elimination from the circulation but the exact structure and functional significance of the circulating N-terminal ANP remains to be established.