Intrinsic rates and adrenergic responses of atria from rats on sprinting, endurance and walking exercise programmes.

The effects of three different physical training programmes on the control of sinoatrial rate in the young male rat were investigated. After training for 8 weeks, 5 d/week, the intrinsic rate and chronotropic response to cumulatively applied norepinephrine (NEp) were examined using isolated atrial preparations. Preparations from animals trained by walking for 60 min/d at 16.1 m/min possessed the same intrinsic atrial rate as sedentary controls, while preparations from an endurance-trained group running for 60 min at 32.2 m/min at 15% grade, and from a sprint-trained group running 50, 10-s efforts at 80.5 m/min, 15% grade with a 30-s rest interval, possessed lower intrinsic atrial rates. Atrial preparations from all groups demonstrated similar maximum rates after application of NEp. For all groups there was no statistically significant difference between the EC50 values for the chronotropic effect of NEp. Training induced a modification in intrinsic atrial rate without influencing NEp chronotropic responses.