Gamma-atrial natriuretic polypeptide (gamma ANP)-derived peptides in human plasma: cosecretion of N-terminal gamma ANP fragment and alpha ANP.

Using RIAs for the N- and C-terminal fragments of the human atrial natriuretic polypeptide (ANP) precursor gamma ANP, that is gamma ANP-(1-25), and alpha ANP [gamma ANP-(99-126)], we studied the secretion of gamma ANP-derived peptides from the heart in normal subjects and patients with heart disease, chronic renal failure, and cirrhosis. We detected gamma ANP-(1-25)-like immunoreactivity (-LI) in plasma from normal subjects (n = 17) in considerable amounts [mean, 510 +/- 62 (+/- SE) pg/mL (174 +/- 21 pmol/L)]; the mean plasma alpha ANP-LI level at the same time in these subjects was 32.8 +/- 4.4 pg/mL (10.7 +/- 1.4 pmol/L). Gel permeation chromatographic analysis of plasma samples from normal subjects and patients with heart disease and chronic renal failure revealed two major components; one was alpha ANP, and the other was the 10K N-terminal gamma ANP fragment (N-peptide) resulting from the removal of alpha ANP (3K) from gamma ANP (13K). In addition, gamma ANP (13K), which possessed both gamma ANP-(1-25)-LI and alpha ANP-LI, and beta ANP, an antiparallel dimer of alpha ANP, were detected in some patients as minor components. A significant positive correlation between plasma levels of the N-terminal gamma ANP fragment and alpha ANP (P less than 0.01) and almost equal step-ups in the coronary sinus plasma levels of the N-terminal gamma ANP fragment and alpha ANP suggest that they are cosecreted in equimolar amounts. The high molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI (17.4 +/- 1.4) in normal subjects and the significantly higher ratio in patients with chronic renal failure (36.9 +/- 7.1; P less than 0.01) suggest the slower clearance of the N-terminal gamma ANP fragment than alpha ANP and a role for the kidney in its degradation. Since the molar ratio of plasma gamma ANP-(1-25)-LI to alpha ANP-LI in patients with cirrhosis (20.7 +/- 2.7) was similar to that in normal subjects, it is unlikely that the N-terminal gamma ANP fragment is metabolized by the liver. In patients with heart disease, plasma gamma ANP-(1-25)-LI and alpha ANP-LI levels were higher in those with cardiac decompensation and were positively correlated with right atrial pressure, pulmonary arterial pressure, and pulmonary capillary wedge pressure, indicating cosecretion of the N-terminal gamma ANP fragment and alpha ANP in response to atrial stretch.(ABSTRACT TRUNCATED AT 400 WORDS)