Shatoor et al J Clin Med Res • 2012;4(3):190-196 Figure 3. Electron micrographs from cardiac atria of amiodarone- and vitamin E-treated rats. A. A semithin section of cardiac muscle showing sarcoplasm of a cardiomyocyte occupied by normal myofibril striations (m), and other myofibrils (stars) appear disrupted. Dissociation of myofibrils in some (stars) and normal pattern (m) in others. B. ANF granules is still less in size (An) while the mito- chondria (M) were preserved with its cristae (Bar = 1 µm). (x: 1000). 1C). The euchromatic nucleus with its nucleolus and closely packed large atrionatriuretic factor (ANF) granules were noted (Fig. 1C). Higher magnification of step-like interca- lated discs was revealed tight junctions and desmosomes (Fig. 1D). Group II (Amiodarone treated rats) Sections from atria of rats administered amiodarone alone, showed ultrastructural changes. Loss of myocardial organi- sation, a scattered area of degenerated cardiomyocytes, and myofibrillar disarray were apparent. Wavy myofibrils, ab- normal pattern of striations, disrupted intercalated discs and abnormal mitochondrial arrangements were identified (Fig. 2A). Myofilaments derangement, partial necrosis, interca- lated disc dissociation and disintegration of filaments were also observed (Fig. 2B). Irregularities of the sarcomere, lower concentration of ANF granules in the perinuclear area and disrupted nuclear chromatin were clearly observed (Fig. 2C). In addition, swollen mitochondria with lysis of its cris- tae and dissolution of the matrix were clearly observed. The intermembrane space of the mitochondria had expanded. In addition, specimens revealed decreased density of the sar- coplasm and marked heterogeneity in the myofibril pattern with ruptures and loss of continuity of the myofilaments (Fig. 2D). Group III (Amiodarone and alpha tocopherol treated rats) Concomitant administration of vitamin E with amiodarone showed a considerable protection of the atrial tissues. Mi- croscopic study of the atrial tissue of this group showed that the sarcoplasm was occupied by normal myofibrils with clear striations and others had been disrupted. These changes did not demonstrate marked cardiac damage as in the amiod- arone-treated group, although occasional focal loss of some myofibrils was observed (Fig. 3A, 3B). There were no altera- tions in mitochondrial morphology compared to the second group (preserved cristae, normal size and shape) (Fig. 3B). Discussion Amiodarone produces its effect as an antiarrhythmic agent by employing different mechanisms of action. It is primarily a potassium channel blocker, but it can also block sodium and calcium channels in addition to beta- and alpha-adrener- gic receptors [25]. The clinical use of amiodarone has been limited to refractory ventricular arrhythmias because of high incidence of side effects, which can be fatal [26]. Most cases of reported amiodarone cardiac toxicity are attributed to its electrophysiological effects, such as bradycardia, heart block and proarrhythmia, whereas the reported histopathologi- cal effects were limited mainly to non-cardiac tissues [27]. Hence, our current study is unique because it is the first in vivo study that demonstrates the ultrastructural changes due to amiodarone in its target cardiac cells. Our study confirmed the toxic effects of amiodarone on mitochondrial morphology. The atrial specimens from the amiodarone-treated group showed swollen mitochondria with lysis of its cristae and dissolution of the matrices. The spaces between the outer and inner membranes of the mito- chondria were clearly enlarged. Our findings support previ- ous reported studies that showed that amiodarone induced perturbations and ultrastructural changes in mitochondrial structure of other non-cardiac tissues [28, 16]. The swelling of the mitochondria could result from failure of the osmotic control mechanism and/or decreased production of adenos- ine triphosphate with subsequent influx of water resulting in breakdown of the inner membranes [29-31]. Furthermore, it is possible that oxidative stress due to an increased amount of oxygen free radicals could cause oxidative damage to the mitochondria and release cytochrome C from mitochondrial Articles © The authors | Journal compilation © J Clin Med Res and Elmer Press™ | www.jocmr.org 193