Atropine-induced bradycardia in the guinea pig: dose-response

The effect of atropine sulfate on the heart rate of the unanesthetized guinea pig was studied using a wide range of doses injected via a chronic jugular cannula; dose-response data are presented for the range of 5 mg/kg to 50 mg/kg. A long-lasting dose-dependent bradycardia was produced. This finding is in contrast to the clasically reported effect of atropine in man and dog: tachycardia sometimes preceded by a transient bradycardia. Thus, the guinea pig may be an excellent model for the study of parasympathomimetic, bradycardia-producing effects of atropine.