Immunoreactive atrial natriuretic factor is present in both atria and ventricles

A comparative study has been made of the amount and form of immunoreactive atrial natriuretic factor (ANF) present in atria versus ventricles in situ and in cultures of atrial and ventricular cardiocytes in rats of various ages: foetus (-2 days of age), newborn (3 days of age), 10 days, 35 days and 70 days old. It was first established that ANF is present in the circulation at all ages investigated, the highest levels being found in the foetus. The atrial content of ANF increased gradually with time and was always in the microgram range. In ventricles, where it was in the nanogram range, total ANF increased with age. More ANF was found in the right than in the left atrium at all ages except in the foetus where the reverse was true. In ventricles, ANF was distributed equally between right ventricle, left ventricle and septum in the foetus, the newborn and in the adult. At 10 days and 35 days, ANF was unequally distributed: (right ventricle greater than septum greater than left ventricle). In cultured atrial cardiocytes, ANF was more abundant than in cultured ventricular cardiocytes at all ages and the amount decreased with the age of the donor animals. Atrial cardiocytes secreted more ANF than did ventricular cardiocytes at all ages investigated, the amount secreted generally decreasing with the age of the donor animals. The secretory activity of atrial cardiocytes per hour was also higher than that of their ventricular counterparts; over this time period, both types of cells secreted more ANF in the presence of serum.(ABSTRACT TRUNCATED AT 250 WORDS)