Structure, Expression, and Function of Atrial Natriuretic Factor in Extraatrial Tissues*

I. Introduction THE MAINTENANCE of water and salt balance in the continuously changing conditions of external and internal environment is one of the most important body functions. This function is maintained by the complex interplay of several neuronal and hormonal systems such as renin-angiotensin-aldosterone, vasopressin, and a recently discovered cardiac hormone. Indeed, cardiac myocytes synthesize and secrete into the blood stream (1) a biologically potent peptide, atrial natriuretic factor (ANF), whose existence was first discovered by de Bold and co-workers in 1981 (2). ANF in a 28 amino acid (AA) peptide (ANF-99-126)1 which is present at the carboxyl end of a larger precursor molecule [(ANF 1-126; (3)]. The peptide has been found and characterized in the heart of several mammalians (including human, rat, rabbit, bovine, etc.) birds and amphibians (4) and complementary DNA (cDNA) and genomic clones encoding the ANF precursor have been obtained from several species (5). The ANF sequence is highly con...