1. We have developed a radioimmunoassay for the measurement of immunoreactive brain natriuretic peptide (1–32) in human plasma. Simultaneous measurements of atrial natriuretic peptide have also been carried out to allow for direct comparison between circulating brain natriuretic peptide and atrial natriuretic peptide. Plasma levels of immunoreactive brain natriuretic peptide (means ± sem) were 1.1 ± 0.1 pmol/l in 36 normal healthy subjects and were significantly elevated in cardiac transplant recipients (18.8 ± 3.9 pmol/l, n = 12) and in patients with dialysis-independent (8.8 ± 1.5 pmol/l, n = 11) or dialysis-dependent (41.6 ± 8.8 pmol/l, n = 14) chronic renal failure. Similarly, in these groups of patients plasma levels of atrial natriuretic peptide were also significantly raised when compared with those in the group of normal healthy subjects.
2. The plasma level of atrial natriuretic peptide was significantly higher than that of brain natriuretic peptide in normal subjects and in patients with dialysis-independent chronic renal failure, with ratios (atrial natriuretic peptide/brain natriuretic peptide) of 2.8 ± 0.2 and 2.2 ± 0.3, respectively. However, in both cardiac transplant recipients and patients on dialysis plasma levels of atrial natriuretic peptide and brain natriuretic peptide were similar, with ratios of 1.3 ± 0.2 and 1.0 ± 0.1, respectively, in these two groups.
3. Plasma levels of brain natriuretic peptide and atrial natriuretic peptide were significantly correlated in the healthy subjects and within each group of patients. When all groups were taken together, there was an overall correlation of 0.90 (P<0.001, n = 73).
4. Patients on dialysis had the highest plasma levels of both brain natriuretic peptide (41.6 ± 8.8 pmol/l, n = 14) and atrial natriuretic peptide (41.3 ± 9.4 pmol/l, n = 14) and the levels of both peptides declined significantly after maintenance haemodialysis. However, the overall percentage decrease in the plasma level of atrial natriuretic peptide (43.6 ± 7.5%) after dialysis was significantly greater than that observed for brain natriuretic peptide (15.9 ± 5.3%, P<0.005).
5. Displacement curves of iodinated atrial natriuretic peptide from bovine adrenal membranes by human atrial natriuretic peptide (99–126) and human brain natriuretic peptide (1–32) gave a median inhibitory concentration of 144 pmol/l for atrial natriuretic peptide and 724.4 pmol/l for brain natriuretic peptide. The cross-reactivity of human brain natriuretic peptide with the atrial natriuretic peptide receptor preparation was 19.5% of that of atrial natriuretic peptide, indicating that human brain natriuretic peptide has a lower binding affinity for the atrial natriuretic peptide receptor/binding site on bovine adrenal membranes.
6. These results suggest that brain natriuretic peptide is co-secreted with atrial natriuretic peptide and may also be an important factor in the adaptive mechanisms to impairment of renal function. However, whether brain natriuretic peptide has an independent and fundamentally important role in man remains to be investigated.