Abstract 008: Aldosterone Contributes to the Blood Pressure Elevation, Endothelial Dysfunction, and Norepinephrine Sensitivity Caused by Endothelial Human Endothelin-1 Overexpression in Mice

Abstract

Background: The mechanisms of blood pressure (BP) regulation by endothelin (ET)-1 produced by endothelial cells (ECs) are complex and remain unclear. Transgenic mice with tamoxifen-inducible EC-restricted human ET-1 overexpression (ieET-1) exhibited BP elevation 3 months after induction. ET-1 has been shown to stimulate the release of aldosterone from adrenal cortex (AC). Whether aldosterone plays a role in EC ET-1 overexpression-induced BP elevation and vascular injury is still unknown. Methods and results: Nine to 12-week-old male ieET-1 mice and control ieCre mice expressing a tamoxifen-inducible Cre recombinase under the control of EC-specific Tie2 promoter were treated with tamoxifen (1 mg/kg/day, SC) for 5 days and studied 3 months later. Plasma aldosterone levels measured by ELISA was increased in ieET-1 vs. ieCre mice (1.21±0.14 vs. 0.70±0.09 ng/mL, P <0.05). Reverse transcription-quantitative PCR (RT-qPCR) showed that aldosterone synthase ( Cyp11b2 ) was decreased in AC of ieET-1 vs. ieCre mice (fold change: 0.52±0.06 vs. 1.00±0.16, P <0.01). CYP11B2 protein levels measured by Western Blotting was unchanged. Treatment with mineralocorticoid receptor antagonist eplerenone (100 mg/kg/day) during the last 2 weeks decreased daytime systolic BP determined by telemetry in ieET-1 vs. ieCre mice (Systolic after 14 days [mm Hg]: 128±1.6 vs. 137±1.8, P <0.01). The EC50 concentration for norepinephrine-induced MA contraction was reduced in ieET-1 vs. ieCre mice (EC50 [mol/L]: 5x10 -7 ±6x10 -8 vs. 4x10 -6 ±7x10 -7 , P <0.05), which was reversed by elplerenone (EC50 [mol/L]: 8x10 -6 ±5x10 -6 , P <0.05). The MA relaxation response to acetylcholine was decreased in ieET-1 vs. ieCre mice (32.2±5.3% vs. 70.5±5.9%), effect that was reduced by eplerenone (43.1±5.5%). The MA endothelium-independent relaxation response to sodium nitroprusside (SNP) was similar in ieET-1 and ieCre mice. Eplerenone enhanced sensitivity to SNP in iET-1 mice (EC50 [mol/L]: 3x10 -8 ±1x10 -8 vs. 1x10 -7 ±2x10 -8 , P <0.05). Conclusions: Increased aldosterone production contributes to EC human ET-1 overexpression-induced daytime SBP elevation, enhanced contractile response to norepinephrine and endothelial dysfunction.