Evidence of Parasympathetic Activity of the Angiotensin Converting Enzyme Inhibitor, Captopril, in Normotensive Man

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Abstract
Captopril (50 mg orally) produced a significant fall in systolic and diastolic blood pressure in 6 normotensive Na replete subjects, without a rise in heart rate. On captopril, there was no change in the expected normal increase in heart rate on standing. Supine plasma noradrenaline [norepinephrine] was not reduced by captopril and normal postural increases were maintained. Atropine (0.04 mg/kg i.v.) reduced the difference in blood pressure change between captopril and placebo. Facial immersion in water produced a bradycardia. This change was abolished by atropine and attenuated both by captopril and edrophonium (10 mg i.v.), a cholinesterase inhibitor. Lying down after 6 min standing produced an immediate transient tachycardia, which was abolished by atropine and attenuated by captopril. Blood pressure and heart rate rose after a cold pressor test on both captopril and placebo. The tachycardia during the Valsalva maneuvre was inhibited by edrophonium and to a lesser extent by captopril. The effects of captopril and edrophonium were additive. Parasympathetic activity of captopril may contribute to its hemodynamic profile.