Atrial natriuretic polypeptides (ANP): rat atria store high molecular weight precursor but secrete processed peptides of 25-35 amino acids.

A radioimmunoassay was developed for rat atrial natriuretic polypeptides. Using the radioimmunoassay and gel filtration in reducing and dissociating conditions, extracts of rat atria were found to contain mainly a 15000-dalton immunoreactive material, probably corresponding to pronatriodilatin. However, when isolated beating atria were incubated in plasma-free conditions, the secreted immunoreactive material consisted almost exclusively of 2500-3500-dalton peptide(s). These results show that rat atrial cells secrete a low molecular weight natriuretic peptide which is highly active, but store the less active large molecular weight form(s).