Big ANF: large-molecular-weight ANF in rabbit plasma. II. Acid dissociation and HPLC of dissociated irANF.

A large-molecular-weight form of atrial natriuretic factor (ANF) was found in rabbit plasma. When extraction of plasma utilizing octadecylsilane cartridges is employed, this big ANF is not retained by the cartridge. When this material is dissociated with acid, immunoreactive ANF (irANF) is released. Of the acids tested, formic and acetic acid (0.05 M) were indicated as the most effective in causing the dissociation. High-performance liquid chromatography analysis of dissociated ANF, confirmed by coelution with synthetic peptides, disclosed the presence of ANF-(99-126) and ANF-(103-126) in a ratio of approximately 2:1. Atriopeptin I was detected in most of the samples analyzed, but atriopeptin II was only detected in one analysis. Despite the wide spectrum of the antiserum used for detection of irANF in the eluent fractions, only immunoreactive peaks coeluting with the four standards were detected. We therefore conclude that big ANF is a bound form of atrial peptides found in normal circulation.