SEM/TEM investigation of rat cardiac subcellular alterations induced by changing duration of noise stress.

Abstract

Many studies have shown that loud noise is an environmental stressor. Noise exposure causes changes at different levels in living beings; the cardiovascular system, considered to be the most affected apparatus, has received much attention in both animals and humans. The present study investigated the effect of changing duration of noise stimulation on rat myocardium to determine whether the responses could be related to time. The study was performed on young albino male rats. Three groups of animals were exposed to white noise (100 dBA) for 1, 6, and 12 hr, respectively, and samples of right atrium and ventricle were processed for ultrastructural examination. The subcellular organization of cardiomyocytes was examined by transmission and scanning electron microscopy, the latter being carried out with the modified osmium maceration method. After 1 hr of noise exposure, atrial and ventricular cardiomyocytes did not present significant alterations. After 6 hr, changes were observed in atrial tissue at the mitochondrial level, whereas the ventricular structure appeared unaffected. After 12 hr of treatment, in addition to the mitochondrial alterations, changes in atrial and ventricular myocardium, consisting of areas of enlargement in intercalated disc membranes and decreased density in sarcoplasm, were detected. The methods we applied for the visualization of cellular organelles allowed us to demonstrate that atrial tissue is primarily involved in stress response, especially at the mitochondrial level; a more prolonged time of exposure seems to be necessary for ventricular involvement.