Immunoreactive prohormone atrial natriuretic peptides 1–30 and 31–67: Existence of a single circulating amino-terminal peptide

Sep-Pak C18 extraction of human plasma and radioimmunoassay using antibodies which recognize atrial natriuretic peptide (99–128) and the prohormone sequences 1–30 and 31–67 resulted in mean values from 20 normal subjects of 26.2 (±9.2), 362 (±173) and 368 (±160) pg/ml, respectively. A high correlation coefficient between values obtained using antibodies recognizing prohormone sequences 1–30 and 31–67 was observed (R=0.84). Extracted plasma immunoreactivity of 1–30 and 31–67 both eluted at 46% acetonitrile. In contrast, chromatographic elution of synthetic peptides 1–30 and 31–67 was observed at 48 and 39% acetonitrile, respectively. Data suggest that the radioimmunoassay of plasma using antibodies recognizing prohormone sequences 1–30 and 31–67 may represent the measurement of a unique larger amino-terminal peptide fragment containing antigenic sites recognized by both antisera.