Role for Endothelin-1 in Angiotensin II-mediated Hypertension

Experiments in cultured vascular smooth muscle cells have shown that angiotensin II (Ang II) stimulates expression of endothelin-1. We sought to examine role of endothelin-1 in the effects of Ang II in vivo. Ang II infusion in rats (0.7 mg/kg per day for 5 days) was associated with marked increases in vascular smooth muscle endothelin-1 levels, as assessed by immunostaining. Administration of the selective endothelin type A (ET(A)) receptor antagonist PD 155080 (50 mg/kg per day) abrogated the hypertensive response to a 5-day infusion of Ang II (0.7 mg/kg per day), as did losartan (25 mg/kg per day). ET(A) receptor blockade during Ang II-mediated hypertension was associated with marked elevations of plasma endothelin-1 levels. Ang II-mediated hypertension was associated with heightened vascular responsiveness to a variety of vasoconstrictor agents except endothelin-1. Blockade of ET(A) receptor invariably corrected this vasoconstrictor hyperresponsiveness. We conclude that some of the vascular effects of Ang II thought to be unique to this hormone are likely mediated by endothelin-1.