Pro-atrial natriuretic peptide (1-98): the circulating cardiodilatin in man

The nature of plasma cardiodilatin, the amino-terminal product of the human pro-atrial natriuretic peptide, was investigated by two separate radioimmunoassays directed against the N-terminal and the putative C-terminal of the cardiodilatin molecule: ANP-[Asn1-Lys16] and ANP-[Lys87-Arg98], respectively. Serial dilutions of normal and cardiac failure plasma exhibited parallelism with the synthetic peptide standard curves in both assays. The concentrations of N- and C-terminal cardiodilatin-immunoreactivity equivalents (-IE) were significantly higher in cardiac failure patients. N-terminal-IE: 912 +/- 87, normal subjects 129 +/- 13 (mean +/- SEM); C-terminal-IE: 7979 +/- 1784, normal subjects 895 +/- 213 (both p less than 0.001). Although the concentrations determined by the two assays were not identical, significant correlations were found between them in both normal subjects (r = .69, p less than 0.001) and cardiac failure patients (r = .72, p less than 0.01). Characterisation by gel permeation and fast protein liquid chromatography demonstrated coelution of the N- and C-terminal cardiodilatin immunoreactivities in a single chromatographic peak. These results suggest that the circulating cardiodilatin in normal subjects and patients with cardiac failure contains the entire prohormone amino-terminal sequence ANP-[Asn1-Arg98].