Effects of angiotensin II on nitric oxide generation in growing and resting rat aortic endothelial cells

Objectives To assess the effects of anglotensin II (ang II) and its receptors on nitric oxide (NO) production and endothelial NO synthase (eNOS) activity and expression with respect to rat aortic endothelial cell (RAEC) growth. To also assess whether an intact endothelium is required for ang II activity. Methods RAEC were treated with different doses of ang II, Ca2+ ionophore A23187, valsartan (an AT(2) receptor inhibitor) or PD-123319 (an AT(2) receptor inhibitor) alone or in combination for 24 h before measuring nitrite levels by Griess reaction as an index of NO production and eNOS activity by L-[H-3]-arginine to L-[H-3]-citrulline conversion assay. eNOS mRNA and protein expressions were determined by Northern and Western analyses, respectively. The requirement of endothelium for ang II-mediated relaxant/contractile effects was investigated by isometric tension studies. Results NO production and eNOS activity/expression were almost two-fold greater in proliferating RAEC. Ang II or Ca2+ ionophore A23187 enhanced NO production in proliferating and confluent RAEC without altering the folddifference in basal NO release. Both valsartan and PD123319 significantly diminished NO production in RAEC treated with ang II but not Ca2+ ionophore A23187 while N-G-nitro-L-arginine (L-NNA, 10 mumol/l) equally decreased NO generation in response to both stimulators. L-NNA, valsartan and PD-123319 also abolished endothelium-dependent vasorelaxant responses to ACh and Ca2+ ionophore A23187 in the presence of ang II. Sodium nitroprusside (SNP), a NO donor, increased endothelium-independent vasorelaxant responses that were augmented by valsartan but not L-NNA or PD-123319 in the presence of ang II. Conclusions Ang II induces vascular NO production through endothelial AT(1) and AT(2)-receptors. This may be beneficial in counterbalancing its vasoconstrictor effect on vascular smooth muscle cells. (C) 2003 Lippincott Williams Wilkins.