The influence of spasmolytic agents on heart rate variability and gastrointestinal motility in normal horses

The effects of hyoscine-N-butylbromide (hyoscine) and propantheline-bromide (propantheline) on heart rate (HR), HR variability (HRV) and gastrointestinal tract (GIT) contractions in the normal horse were determined. Five adult horses had ECG recordings for 180 min after treatment with propantheline (100 mg), hyoscine (120 mg) or saline. Both propantheline and hyoscine reduced GIT sounds, with propantheline having a longer duration of effect (⩾120 min). Both drugs elevated HR relative to the control baseline period (P < 0.05), with the effects of propantheline again being of longer duration. HRV analysis indicated that propantheline suppressed Total Power (P < 0.05), and both the high frequency (HF) and low frequency (LF) components of the power spectral analysis for up to 60–90 min post treatment. Hyoscine had no effect on HRV Total Power but reduced the HF component for 30 min after drug injection. Time domain variables correlated with Total Power and HF data (P < 0.01). The marked effect of these compounds on parasympathetic control of cardiac and GIT function in normal horses should be taken into consideration when evaluating a clinical response to these agents.