Tissue fractionation studies on the relationship between an atrial natriuretic factor and specific atrial granules

Mammalian atrial cardiocytes contain storage granules, the specific atrial granules, which morphologically resemble granules found in polypeptide hormone producing cells. The number of these granules may be altered by manipulation of water-electrolyte balance in experimental animals hinting at a role for atrial granules in the regulation of such balance. It has been recently shown that rat atrial muscle contains a factor referred to as atrial natriuretic factor. This factor induces a very powerful diuretic and natriuretic response when injected into nondiuretic assay rats. The present investigations were carried out to determine whether there exists any relationship between atrial natriuretic factor and specific atrial granules. Using a tissue fractionation procedure for the isolation of purified rat atrial granules, it was found that the highest relative purification of natriuretic factor was obtained in granule-rich subfractions. This finding suggests that the specific atrial granules may be a storage site for atrial natriuretic factor.