Qualitative and quantitative analysis of granules in atrial appendage cardiocytes in different physiological states

Atrial appendage cardiocytes of mammals, including man, contain multiple cytoplasmic granules that vary in number in different physiological states. Using morphologic and comprehensive morphometric techniques, these granules were assessed in Sprague-Dawley rats following dehydration for 5 days, volume-loading by substituting 1% NaCl as drinking water for 7 days, unilateral nephrectomy plus volume-loading for 7 days, and in late term pregnant animals (18-20 days; term approximately 21 days). Although principally located in the paranuclear region, granules were observed throughout the sarcoplasm. Cytological features indicative of synthetic activity and granule formation were readily apparent in all groups with the exception of pregnant rats where they were infrequently observed. Granule contents were released by exocytosis and observed in the right appendage of control, dehydrated and nephrectomy/volume-loaded groups and left appendage of volume-loaded animals. Exocytosis was not observed in pregnant animals. By point counting, the proportional volume of cardiocytes occupied by granules (Vv) in controls was significantly greater for right than for left appendage (2.12 +/- 0.22% vs 1.29 +/- 0.16%; mean +/- SEM; p less than 0.05). A significantly similar difference was found for nephrectomy/volume-loaded animals. There was no significant difference in Vv for right appendage between the control and experimental groups; for left appendage there was a significant increase in Vv to 2.42 +/- 0.09% (p less than 0.05) for volume-loaded animals only. Estimation of the maximum diameter of granule profiles in control animals was 238 +/- 9 nm and 230 +/- 6 nm for right and left appendages, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)