1. C-type natriuretic peptide is a neuropeptide, which is also produced by the vascular endothelial cells. Plasma immunoreactive C-type natriuretic peptide concentrations in patients with various diseases have not yet been studied.

2. Plasma immunoreactive C-type natriuretic peptide concentrations were studied by radioimmunoassay in normal subjects, patients with congestive heart failure, non-dialysed patients with chronic renal failure and haemodialysis patients with chronic renal failure. The C-type natriuretic peptide levels were compared with the levels of atrial natriuretic peptide and brain natriuretic peptide.

3. Plasma immunoreactive C-type natriuretic peptide concentrations were greatly elevated in patients with chronic renal failure [non-dialysed, 13.0 ± 4.2 pmol/l (mean ± SEM), n = 9, P < 0.01) compared with normal subjects (4.4 ± 0.4 pmol/l, n = 26); haemodialysis, 16.1 ± 2.1 pmol/l, n = 13, P < 0.01], but not in patients with congestive heart failure (New York Heart Association Class II-IV, 3.0 ± 0.7 pmol/l, n = 11, P > 0.05). Plasma immunoreactive atrial natriuretic peptide and brain natriuretic peptide concentrations were elevated both in patients with congestive heart failure and in haemodialysis patients with chronic renal failure.

4. Reverse-phase high performance liquid chromatography showed that immunoreactive C-type natriuretic peptide in plasma from normal subjects and haemodialysis patients was eluted in the positions of C-type natriuretic peptide −22 and −53.

5. These findings suggest that C-type natriuretic peptide is a non-cardiac circulating hormone and participates in the cardiovascular regulation in a different manner from atrial natriuretic peptide and brain natriuretic peptide.

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