Angiotensin II relaxations of bovine adrenal cortical arteries: role of angiotensin II metabolites and endothelial nitric oxide.

Angiotensin (Ang) II regulates adrenal steroidogenesis and adrenal cortical arterial tone. Vascular metabolism could decrease Ang II concentrations and produce metabolites with vascular activity. Our goals were to study adrenal artery Ang II metabolism and to characterize metabolite vascular activity. Bovine adrenal cortical arteries were incubated with Ang II (100 nmol/L) for 10 and 30 minutes. Metabolites were analyzed by mass spectrometry. Ang (1-7), Ang III, and Ang IV concentrations were 146+/-21, 173+/-42 and 58+/-11 pg/mg at 10 minutes and 845+/-163, 70+/-14, and 31+/-3 pg/mg at 30 minutes, respectively. Concentration-related relaxations of U46619-preconstricted cortical arteries to Ang II (maximum relaxation=29+/-3%; EC(50)=3.4 pmol/L) were eliminated by endothelium removal and inhibited by the NO synthase inhibitor, nitro-L-arginine (30 micromol/L; maximum relaxation=14+/-7%). Ang II relaxations were enhanced by the angiotensin type-1 receptor antagonist losartan (1 micromol/L; maximum relaxation=41+/-3%; EC(50)=11 pmol/L). Losartan-enhanced Ang II relaxations were inhibited by nitro-L-arginine (maximum relaxation=18+/-5%) and the angiotensin type-2 receptor antagonist PD123319 (10 micromol/L; maximum relaxation=27+/-5%). Ang (1-7) and Ang III caused concentration-related relaxations with less potency (EC(50)=43 and 24 nmol/L, respectively) but similar efficacy (maximum relaxations=39+/-3% and 48+/-5%, respectively) as losartan-enhanced Ang II relaxations. Ang (1-7) relaxations were inhibited by nitro-L-arginine (maximum relaxation=16+/-4%) and the Ang (1-7) receptor antagonist 7(D)-Ala-Ang (1-7) (1 micromol/L; maximum relaxation=10+/-3%) and eliminated by endothelium removal. Thus, Ang II metabolism by adrenal cortical arteries to metabolites with decreased vascular activity represents an inactivation pathway possibly decreasing Ang II presentation to adrenal steroidogenic cells and limits Ang II vascular effects.