Physical exercise attenuates the cardiac autonomic deficit induced by nitric oxide synthesis blockade.

Background: The nitric oxide (NO) synthesis blockade is characterized by an increase in the cardiac sympathetic activity and the physical training promotes the decrease in the sympathetic activity.

Objective: We investigated the effect of the NO synthesis blockade on the autonomic cardiovascular control in rats submitted to aerobic exercises during a 10-week period.

Methods: Male Wistar rats were divided in four groups: control rats, treated with chow food and water ad libitum for 10 weeks (CR); control rats, treated with N G-nitro-L-arginine methyl ester (L-NAME) during the last week (CRL); rats trained during 10 weeks on an electrical treadmill (TR); rats trained for 10 weeks and treated with L-NAME during the last week (TRL). The autonomic cardiovascular control was investigated in all groups with the use of a double blockade with methylatropine and propranolol and analysis of variability.

Results: The CRL and TRL groups presented hypertension. The CRL group presented tachycardia and predominance of the sympathetic tonus in heat rate (HR) measurement after the pharmacological autonomic blockade. The TR group presented bradycardia and lower intrinsic HR when compared to the others. The evaluation of the HR variability showed lower absolute and normalized values in the low frequency (LF) band in the CRL group. On the other hand, the TRL presented an increase in the LF band in absolute values. The analysis of variability of the systemic arterial pressure (SAP) showed that the CRL and TRL groups presented higher values in the LF band.

Conclusion: The previous physical exercise prevented the deficit in the autonomic cardiac control induced by the treatment with L-NAME, but did not prevent the increase in the SAP variability.