Abstract
The vagal component of the chronotropic response to baroreceptor stimulation in normal man was evaluated by measuring responses of heart rate and arterial pressure to the intravenous administration of the alpha-adrenergic stimulator methoxamine in the presence of total preganglionic sympathetic denervation produced by spinal anesthesia. Mean arterial pressure increased an average of 20.5 per cent with methoxamine. This was associated with a 26.5 per cent decrease in heart rate. Methoxamine-induced bradycardia observed during sympathetic denervation was abolished when total sympathetic denervation was combined with parasympathetic inhibition (atropine). It is concluded that in normal man vagal parasympathetic impulses contribute to the development of the reflex bradycardia associated with elevation of arterial pressure.
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