Angiotensin II increases the release of endothelin-I from human cultured endothelial cells but does not regulate its circulating levels

We investigated the effect of angiotensin II on endothelin-1 secretion in vitro and in vivo. In vivo, angiotensin II was given intravenously to 23 essential hypertensive and 8 control subjects according to different protocols: Study A, 1.0 ngċmin^-1ċkg^-1 and 3.0 ngċmin^-1ċkg^-1 angiotensin II for 30 min each; Study B, 1.0 ngċmin^-1ċkg^-1 and 3.0 ngċmin^-1ċkg^-1 angiotensin II for 120 min each; Study C, 3.0 ngċmin^-1ċkg^-1 angiotensin II for 30 min followed by a dose increment of 3.0 ngċmin^-1ċkg^-1 every 30 min until mean blood pressure levels increased by 25 mmHg; Study D, 1.0 ngċmin^-1ċkg^-1 followed by 3.0 ngċmin^-1ċkg^-1 angiotensin II for 60 min each on two different NaCl diets (either 20 mmol NaCl/day or 220 mmol NaCl/day, both for 1 week). In all in vivo studies neither plasma nor urine endothelin-1 levels changed with angiotensin II infusion. In contrast, angiotensin II (10^-9, 10^-8, 10^-7 mol/l) stimulated endothelin-1 secretion from cultured human vascular endothelial cells derived from umbilical cord veins in a time- and dose-dependent manner. The in vitro angiotensin II effects were abolished by candesartan cilexetil, an inhibitor of the membrane-bound AT₁ receptor, and also by actinomycin D, an RNA synthesis inhibitor, and cycloheximide, a protein synthesis inhibitor, indicating that endothelin-1 release depended on AT₁ receptor subtype and de novo protein synthesis. Our findings indicate that angiotensin II regulates endothelin-1 release by cultured endothelial cells through an AT₁ receptor-dependent pathway, but does not influence circulating endothelin-1 levels in vivo.