Inhibition of the baroreceptor heart rate reflex by angiotensin II in normal man

Eight normotensive male subjects were infused with angiotensin II or phenylephrine in a single blind fashion. Measurements were made of blood pressure and pulse interval every 3 min, and blood drawn for plasma catecholamines at the beginning and end of the infusion. Phenylephrine produced a rise in blood pressure which was associated with a bradycardia in all subjects. A statistically significant relationship between blood pressure and pulse interval was observed in all subjects. In contrast, angiotensin II infusion produced an equal pressor response, but the change in pulse interval was statistically significantly less than that seen following phenylephrine infusion. In seven of eight subjects no significant relationship was observed between blood pressure and pulse interval. Plasma noradrenaline levels were similar before each pressor infusion and were unchanged during each infusion. These observations are consistent with central inhibition of the baroreceptor heart rate reflex by angiotensin II in man.