Exhaustive Exercise On The Rat Cardiac Conduction System

Objective To explore the effect of exhaustive exercise on the cardiac conduction system, the changes of histology, histochemistry and ultrastructure were observed in the SAN, AVN and AVB after rats' exhaustive swimming.Method After the last exercise of rats ECG was tested, then SAN, AVN and AVB were cut off. These specimens were treated respectively with regular procedures of paraffin sections, transmission electron microscope and enzyme histochemistry. The paraffin sections were stained by HE, Masson and Nagar-Olsen stains. The TEM specimens were stained by uranyl and lead citrate. The others were stained by glycogen, lactate dehydrogenase, succinate dehydrogenase, monoamine oxidase, acetyl cholinesterase and alkaline phosphatase.Result (1)ECG showed that rat's heart rate was increased after medium intensity exercise, but after the single exhaustive swimming the heart rate decreased, the duration of P, T wave and P-R, QRS, Q-T, P-J interval prolonged, amplitude of P, T and R increased, J point elevated, R and T wave mixed together, the ratio of J/R increased. After seven consecutive daily exhaustive swimming the changes of ECG were similar to CG, but less severe than the SESG. (2)The AN showed that the amount of myofilalments and mitochondria in cells were increased after medium intensity exercise; but were dissolved after the single exhaustive swimming, and cytoarchitecture injury in SAN was as follows: atrial fibers >T cells >P cells. After seven consecutive daily exhaustive swimming cytoarchitecture had lower damage level than SESG P and T cells showed that the amount of myofilalments were increased and irregularly arranged. The amount of mitochondria were increased but showed more degeneration, and less density of crista. The irregular arrange and abnormal junctions between cells and more apoptosis were observed. The histochemical stain showed that after medium intensity exercise the content of glycogen in SAN was reduced and the activity of MAO and AKP were increased. After the single exhaustive swimming the content of glycogen, the activity of SDH, MAO and ACHE was decreased, while LDH increased. Compared with the SESG, after seven consecutive daily exhaustive swimming, content of glycogen, the activity of ACHE and AKP was increased, while LDH, SDH and MAO decreased. (3)The changes of AVN were similar to SAN. After the single exhaustive swimming the T cells showed cloudy swelling, while the changes of T cells was complicated, some myofilalments irregularly arranged, some granular degeneration, andmore apoptotic cells. The change of histochemistry were similar to SAN, while after medium intensity exercise the activity of MAO and ACHE were no significant change and the activity of AKP increased. The changes of AVB were similar to AVN, but after exhaustive exercise the pathological change were more severe than AVN.Conclusion (1) After medium intensity exercise the excitability and conductivity of self-excitable cell was increased. The automaticity of self-excitable cell and velocity of sino-atrial and atrial-ventricular conduction was decreased, and the time of depolarization and repolarization of atrium and ventricle were prolonged, and the ventricle myocardial ischemic-anoxic injury under the endocardium was aggravated after the single exhaustive swimming. After seven consecutive daily exhaustive swimming self-excitable cells showed some adaptive changes to ultrastructure. (2) After medium intensity exercise cytoarchitecture of SAN showed some adaptive changes to exercise load, and glycogen consumed , sympathetic activity and capability of transmembrane transport enhanced. After the single exhaustive swimming, cytoarchitecture showed injury changes in SAN, while P and T cells injury caused by exhaustive exercise had slighter than atrial muscle cells, and glycogen largely consumed, the capacity of aerobic metabolism reduced, anaerobic metabolism improved, the sympathetic and the vagal activity diminished and capillaries damaged. After seven consecutive daily exhaustive swimming the injury of...