Electron microscopic analysis of the specific granule content of human atria: An investigation of the role of atrial pressure and atrial rhythm in the release of atrial natriuretic peptide
Knowledge about the stimulus for the release of atrial natriuretic peptide (ANP) from human atria is incomplete. Atrial stretch is known to be a stimulus and atrial tachyarrhythmias are thought to be another. The effects of atrial size (by twodimensional echocardiography) and atrial fibrillation on the atrial specific granule content of human atria were studied to gain insight into the secretory mechanisms of ANP. An electron microscopic analysis of the atrial granule content was used to study 12 patients - 5 with mitral stenosis and sinus rhythm, 3 with mitral stenosis and atrial fibrillation and 4 controls. Granules were counted using a free count and montage method.
This is the first report of such a morphometric analysis in humans. Granule counts were significantly raised in the patients with mitral stenosis compared with controls (P < 0,014). This observation probably reflects a high turnover state induced by elevated atrial pressures. Further support for this conclusion is provided by the demonstration of a positive correlation between granule counts and left atrial size (r = 0,86; P < 0,01). The tendency for higher counts in patients with atrial fibrillation may be related to the rhythm disturbance itself, but clinical and echocardiographic data suggest more severe atrial pressure overload in this group.