Mechanisms of release of atrial natriuretic factor in vivo.

The aim of the study was to define the relationship between the concentration of immunoreactive atrial natriuretic factor (ANF) in the plasma and atrial stretch, atrial pressure and atrial wall stress during changes in blood volume within the physiological range. Advantage was taken of the potentiation of the release of ANF, in response to blood volume expansion, in the anaesthetized rabbit, by section of the carotid sinus, aortic depressor and vagus nerves. Mean arterial pressure and right and left atrial pressures were measured. Right and left atrial dimensions were measured by sonomicrometry. Blood volume was expanded by 20% and then decreased at 1% of the blood volume per minute for 40 min, before and after section of the nerves. Plasma ANF did not change significantly in response to either the increase or decrease in blood volume in the presence of intact nerves. After the nerves were sectioned, blood volume expansion significantly increased IR-ANF (34.6 +/- 12 to 260.6 +/- 89.8 pg/ml). The relationship between ANF and the changes in left atrial dimensions (extension ratio) was exponential. A significant linear correlation was found between ANF and left atrial pressure and left atrial wall stress. Over a range of atrial pressures from 1-10 cm H2O the atrial wall was extremely distensible, but there were only minor changes in ANF. At higher atrial pressures there was little further extension of the atrial wall but there were much larger increases in plasma ANF. In response to changes in blood volume within the physiological range cardiovascular reflexes normal maintain atrial dynamic function within a narrow range and there is little stimulus for the release of ANF. In conditions in which the cardiovascular reflexes are unable to maintain atrial function constant then there will be changes in the release of ANF and there will be an exponential relationship between atrial wall stretch and plasma ANF.