Differential Effects of Angiotensin-II Compared to Phenylephrine on Arterial Stiffness and Hemodynamics: A Placebo-Controlled Study in Healthy Humans

Abstract

The α1-adrenoceptor agonist phenylephrine (PE) and Angiotensin II (Ang II) are both potent vasoconstrictors at peripheral resistance arteries. PE has pure vasoconstrictive properties. Ang II, additionally, modulates central nervous blood pressure (BP) control via sympathetic baroreflex resetting. However, it is unknown whether Ang II vs. PE mediated vasoconstriction at equipressor dose uniformly or specifically modifies arterial stiffness. We conducted a three-arm randomized placebo-controlled cross-over trial in 30 healthy volunteers (15 female) investigating the effects of Ang II compared to PE at equal systolic pressor dose on pulse wave velocity (PWV), pulse wave reflection (augmentation index normalized to heart rate 75/min, AIx) and non-invasive hemodynamics by Mobil-O-Graph™ and circulating core markers of endothelial (dys-)function. PE but not Ang II-mediated hypertension induced a strong reflex-decrease in cardiac output. Increases in PWV, AIx, total peripheral resistance and pulse pressure, in contrast, were stronger during PE compared to Ang II at equal mean aortic BP. This was accompanied by minute changes in circulating markers of endothelial function. Moreover, we observed differential hemodynamic changes after stopping either vasoactive infusion. Ang II- and PE-mediated BP increase specifically modifies arterial stiffness and hemodynamics with aftereffects lasting beyond mere vasoconstriction. This appears attributable in part to different interactions with central nervous BP control including modified baroreflex function.

Keywords

• α₁-adrenoceptor
• phenylephrine
• Angiotensin II
• baroreflex
• arterial stiffness
• augmentation index