Using two radio-immunoassays for N-terminal and C-terminal fragments of human atrial natriuretic polypeptide (ANP) precursor, γ-hANP [human atrial natriuretic factor- (1-126)], that is γ -hANP(1-25) [human atrial natriuretic factor-(1-25)] and α-hANP [human atrial natriuretic factor-(99-126)], we studied the secretion of γ -hANP-derived peptides into circulation from the heart in normal subjects and patients with essential hypertension and adrenal disorders. Volume expansion with 2 litres physiological saline increased plasma γ -hANP(1-25)-like immunoreactivity concomitantly with plasma α - hANP-like immunoreactivity in normal subjects. Infusion of angiotensin II (20 ng/kg per min) or noradrenaline (200 ng/kg per min) also caused a parallel increase in plasma γ -hANP(1-25)-like and α -hANP-like immunoreactivity. Plasma γ -hANP(1-25)-like immunoreactivity levels were changed together with α -hANP-like immunoreactivity in patients with essential hypertension and adrenal disorders. These results indicate that γ -hANP-derived peptides, α -hANP and the 10-k N- terminal fragment of γ -hANP (N-peptide) are cosecreted from the heart and that the simultaneous measurement of N-peptide and α -hANP serves as an indicator of the cardiac endocrine function. The significance of N-peptide as a hormone must await further clarification.
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