Effect of sympathetic nervous system in running training on cardiac myosin isozyme composition.

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To clarify the relationship between cardiac myosin isozyme composition in running-trained rats and the sympathetic nervous system, we examined whether the sympathetic nervous system could contribute to the modulation of cardiac myosin isozyme in running-trained rats, using atenolol, a selective blocker of cardiac β<SUB>1</SUB> adrenegic receptor. Male Wistar strain rats (4 weeks old) were used, and divided into four groups: control sedentary (CS), control trained (CT), atenolol sedentary (AS), and atenolol trained (AT) . The AS and AT groups were treated with atenolol in drinking water (65 mg/kg/day) for 9 weeks. The CT and AT groups were trained by treadmill running (at 30 m/min for 1 h/day, 5 days/week), starting at 7 weeks old, for 6 weeks. At 13 weeks old, the hearts were excised. The left and right ventricular myosin isozymes were examined by electrophoresis on pyrophosphate gel. The results showed the followings: 1) In the CT and the AT groups, the citrate synthase activities of the plantaris muscle were increased by 26% compared with the CS group (p<0.05) . 2) In the CT group, the running training had no effect on the myosin isozyme composition, in both ventricular muscles. 3) In the AS group, the atenolol treatment resulted in a decrease in the proportion of the V1 myosin and in an increase in that of the V3 myosin. Therefore, the proportion of the β-myosin heavy chain (MHC) in both ventricles of the AS group showed a significant increase compared with the CS group (p<0.05) . 4) The AT group showed a marked increase in the proportion of the β-MHC in both ventricles, compared with that of the AS group, especially in the left ventricle (p<0.05) .<BR>From the results presented here, we did not observe any effect of the sympathetic nervous system on cardiac myosin isozyme composition in the running-trained rats.<BR>It is generally accepted that hemodynamic overload results in an increase in the proportion of β-MHC, and in contrast, the stimulation of the sympathetic nervous system induces an increase in α-MHC. Therefore, we speculated that the effect of running training on cardiac myosin isozyme composition was induced by the effects of both the sympathetic nervous system and hemodynamic overload. Consequently, running training had apparently no effect on myosin isozyme composition.
日本体力医学会の論文

Effect of sympathetic nervous system in running training on cardiac myosin isozyme composition.

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