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One of the main differences between atrial and ventricular cardiocytes is the presence in former of specific granules with morphological characteristics very similar to secretory granules found in peptide-secreting endocrine cells. It has been suggested that these granules are the storage place for the atrial natriuretic factor. In the rat, water deprivation produces an increase in atrial granularity but a significant decrease in acid-extractable diuretic and natriuretic activity, suggesting that the number of atrial specific granules does not necessarily represent natriuretic activity. The atrial natriuretic factor activity is destroyed by incubation with several proteases and does not inhibit the sodium-potassium ATPase, suggesting that the active substance is a small peptide that is probably different from the so-called natriuretic hormone. After a series of chromatographic steps in Sep-Pak cartridges, Bio-Gel P-10, CM Bio-Gel, and Mono S columns, the specific activity of the atrial natriuretic factor was increased from 193, corresponding to atrial homogenates, to 242,000, which corresponds to the last chromatographic step representing a 1250-fold purification. This material showed a potent natriuretic activity, as 10 picomoles increased natriuresis by 100%.
Thibault et al. (Tue,) studied this question.