Radioimmunoassay of Atrial Peptide Blood and Tissue Levels

The observation (DeBold et al. 1981) that mammalian atria contain a peptide that is both natriuretic and diuretic has led to the discovery of a novel endocrine hormone (atriopeptin, AP) which regulates salt and water metabolism from the kidney (Needleman et al. 1985). Atrial extracts were found to be both heat and acid stable (Debold et al. 1981), and to possess spasmolytic activity on vascular smooth muscle (Currie et al. 1983). These bioassays facilitated the purification and sequence analysis of three related peptides, termed AP I, II, and III (Currie et al. 1984 a). Several peptides of different lengths, but sharing a common core sequence to the APs, have been identified by different laboratories. These include cardionatrin (Flynn et a. 1983), atrial natriuretic factor (ANF) (Thibault et al. 1983), atrial natriuretic polypeptide (ANP) (Kangawa and Matsuo 1984), and auriculin (Atlas et al. 1984). cDNA probes were constructed from the peptide sequence and used to determine the sequence for the AP gene (Yamanaka et al. 1984; Maki et al. 1984; Oikawa et al. 1984; Seidman et al. 1984). The AP gene codes for a 152 amino acid preprohormone which contains a hydrophobic 24 amino acid leader sequence (Fig. 1).