Effect of swimming exercise on ultrastructure of atrial muscle of rat

Objective: To explore the effects of different loading swimming exercises on structure of atrial muscle in rat, so as to provide some information for the changes of physiology and pathology by exercise-induced injury and recuperation of cardiac muscle. Method: SD rats were randomly divided into two groups: different loading exercise group and exhaustive exercise group. In the different loading exercise group, the 12-week low, moderate and high loading swimming model was carried out in rats. In the exhaustive exercise group, single exhaustive swimming was carried out in rats. After exercises, rat's atrial muscles were cut off, and treated with routine procedures of transmission electron microscopy before observing the structure of atrial muscle under transmission electron microscope. Result: In low and moderate loading swimming exercise rats, the muscle fibrils arranged orderly, theZlines became thicker and theIbands became wider. The quantities of mitochondria increased, and their cristae arranged densely. The endoplasmic reticulum and Golgi complex revealed high metabolic activity, atrial natriuretic peptide was synthesized and secreted to the outside of cell. The cell junction enhanced. In high loading swimming exercise rats, theZlines of some muscle fibrils became disordered, the nuclear envelope invaginated, the mitochondrion cristae loosened, and the cell junction weakened. For exhaustive swimming exercise rats, the structure of muscle fibrils injured seriously, chromatin condensed, the morphology of some mitochondria changed and their cristae disappeared, while the intact structure of muscle fibrils and mitochondria recovered partly at 24 hours after exhaustive swimming exercise. Conclusion: High loading and exhaustive exercises could destroy the ultrastructure of atrial muscle.