Effect of swimming training on the cardiovascular system in normotensive rats

Resting bradycardia is considered to be a good marker of exercise training (ET) adaptation. However, the time course to heart rate (HR) and blood pressure (BP) responses occur during the exercise training period has not been clarified yet. Therefore, we studied 16 male normotensive Wistar rats. Eight rats were exercise trained (T) for 8 weeks, at a low intensity swimming protocol and 8 were kept sedentary (S). Systolic blood pressure and heart rate were measured two times per week during ET period by caudal measurements. The signal was recorded on a beat-to-beat basis (AT/CODAS) at a frequency of 100 Hz for 30 min in quiet and conscious rats. After ET, an arterial cannula was implanted for direct BP measurements and resting HR was studied using subcutaneously implanted electrodes. After BP and HR measurements, the rats were sacrificed and cardiac chambers were weighed in order to evaluate the cardiac hypertrophy. Maximal citrate synthase activity was measured in the soleus muscle to evaluate the oxidative muscle adaptation. Blood pressure was not changed by swimming training in normotensive rats. As expected, the resting HR was lower in T than in S rats (355±16 vs. 330±20 bpm). We observed increased left ventricle weight/body weight ratio in T rats (1.95 vs. 2.20 g/gBW) which represented 13% of left ventricle hypertrophy in T rats. The maximal citrate synthase activity increased 52% in the T rats. It was concluded that the swimming training for rats is a good experimental model to study the cardiovascular adaptations to dynamic exercise trainin