Atrial natriuretic factor (ANF) is a group of peptides, originally isolated from the cardiac atria, that have a number of important effects on blood pressure, renal function, and salt balance. In the current study, expression of the ANF gene in certain extra-atrial tissues of the rat has been examined by radioimmunoassay of extracted ANF protein and by blothybridization, nuclease S1 analysis, and primer-extension analysis of the ANF mRNA. ANF peptides and mRNA were detected in cardiac ventricles, lung, and pituitary gland at levels generally -<1% those of cardiac atria. The ANF transcripts in extra-atrial tissue appear to be very similar to those synthesized in the atria. They are polyadenylylated, are equivalent in overall length (950-1050 nucleotides), and have identical 5' termini. A secondary transcription start site mapping approximately 80 base pairs upstream from the primary start site is employed in atria and to a lesser extent in other tissues. The ANF transcript is present throughout the cardiac ventricles from apex to base and in the septum as well as the ventricular free walls. The transcript is more prevalent in the left ventricle and interventricular septum than in the right ventricle. Immunocytochemistry using various anti-rat ANF antibodies localized ANF immunoreactivity to the atrial myocytes; the ventricular myocytes, particularly along the endothelial surface of the ventricular chamber; perialveolar cells in the lung; and the gonadotropin-producing cells of the pituitary. The data indicate that the capacity for ANF gene expression extends beyond atrial tissue, albeit at much reduced levels, and may suggest alternative, perhaps paraendocrine, functions for the peptide in these tissues.The atrial natriuretic factor (ANF) consists of a group of peptides with potent diuretic, natriuretic, and vasorelaxant activity (1, 2). As such, they have implied importance as naturally occurring "antihypertensive" regulators of blood pressure, volume status, and cardiovascular homeostasis.Following the description of ANF bioactivity by deBold et al. (1), it was thought that synthesis and secretion of these peptides were confined to the cardiac atria and absent from ventricular as well as other tissues. The atria were found to be rich in secretory granules, while the ventricles were not (3), and atrial extracts had significant natriuretic activity, while no activity was found in ventricular extracts (1,4,5). A number of more recent studies (6-8) also failed to identify either the ANF peptide or its mRNA in the ventricle, as determined by immunocytochemistry and blot hybridization, respectively.Nevertheless, there have been several lines of evidence suggesting that expression of the ANF gene does take place in extra-atrial tissue. First, ANF immunoreactivity has been detected by radioimmunoassay in extracts of rat hypothalamus (9). Second, immunocytochemical studies have revealed several areas in the kidney, adrenal medulla, pituitary (10), and central nervous system, including the hypothalamus (6, 11), t...