Volume 63 (2001) Issue 12 Pages 1359-1360
To investigate the effects of repeated atropine injection on heart rate (HR) variability in resting Thoroughbred horses, two μg/kg of atropine as parasympathetic nervous blockade was injected intravenously every 6 min to a total of 8 μg/kg after intravenous administration of 0.2 mg/kg of propranolol as sympathetic nervous blockade. We recorded electrocardiograms and obtained the HR, then evaluated variation in HR from the power spectrum in terms of low frequency (LF, 0.01-0.07 Hz) power and high frequency (HF, 0.07-0.6 Hz) power. Administration of atropine decreased parasympathetic nervous activity in a dose-dependent manner, affecting first the LF power, then the HF power and finally HR. These responses may provide valuable information for evaluating autonomic nervous activity in Thoroughbred horses.