Stallone J N, Nishimura H, Nasjletti A
Department of Physiology, University of Tennessee-Memphis 38163.
Am J Physiol. 1990 Mar;258(3 Pt 2):R777-82. doi: 10.1152/ajpregu.1990.258.3.R777.
In domestic fowl, angiotensin II (ANG II) produces a unique vasodepressor response in vivo and endothelium-dependent relaxation of aortic rings in vitro that appear to be a direct effect on vascular smooth muscle mediated through vascular angiotensin receptors. To explore the possible role of the endothelium in ANG II-induced vasodilation, ANG II binding to aortic membrane fractions and intact endothelium and prostaglandin (PG) production were examined in fowl aortas. 125I-[Ile5]ANG II binding by endothelium-intact aortic membrane fractions was consistently higher than binding by identically prepared endothelium-deleted membrane fractions at virtually all concentrations of ligand (10 pM-0.20 microM). Incubation of intact aortic rings with 125I-[Ile5]ANG II (0.50 nM) resulted in specific endothelial binding that increased linearly with time from 5.5 +/- 1.7 (SE) fmol/mg protein at 5 min to 13.7 +/- 1.8 at 30 min. Endothelial ANG II binding increased linearly with the dose of ligand, from 2.7 +/- 0.3 fmol/mg protein at 0.1 nM to 21.0 +/- 2.2 at 1.0 nM. Specific ANG II binding to aortic endothelium was competitively displaced 73 +/- 11% by unlabeled ANG II (0.1 microM) but not by bradykinin (0.1 microM). Incubation of intact aortic rings with [14C]arachidonic acid resulted in the formation of radioactive metabolites that comigrated in thin-layer chromatography with authentic PGE2 but not with 6-keto-PGF1 alpha. PGE2 production by aortic rings (44.4 +/- 4.5 ng.mg dry tissue-1.h-1) was not stimulated by addition of ANG II. These results suggest that specific receptors for ANG II exist in fowl aortic endothelium and that PGs are not involved in ANG II-induced vasodilation of the fowl aorta.
在家禽中，血管紧张素II（ANG II）在体内产生独特的血管减压反应，在体外能使主动脉环产生内皮依赖性舒张，这似乎是通过血管紧张素受体对血管平滑肌产生的直接作用。为了探究内皮在ANG II诱导的血管舒张中的可能作用，研究人员检测了家禽主动脉中ANG II与主动脉膜组分及完整内皮的结合情况以及前列腺素（PG）的生成。在几乎所有配体浓度（10 pM - 0.20 μM）下，完整内皮的主动脉膜组分对125I - [Ile5]ANG II的结合始终高于相同制备的去除内皮的膜组分。用125I - [Ile5]ANG II（0.50 nM）孵育完整的主动脉环，会导致特异性内皮结合，其随时间呈线性增加，从5分钟时的5.5±1.7（SE）fmol/mg蛋白增加到30分钟时的13.7±1.8。内皮ANG II结合随配体剂量呈线性增加，从0.1 nM时的2.7±0.3 fmol/mg蛋白增加到1.0 nM时的21.0±2.2。未标记的ANG II（0.1 μM）能竞争性取代73±11%的主动脉内皮特异性ANG II结合，但缓激肽（0.1 μM）则不能。用[14C]花生四烯酸孵育完整的主动脉环，会形成放射性代谢产物，这些产物在薄层色谱中与 authentic PGE2迁移一致，但与6 - 酮 - PGF1α不一致。添加ANG II不会刺激主动脉环生成PGE2（44.4±4.5 ng·mg干组织-1·h-1）。这些结果表明，家禽主动脉内皮中存在ANG II的特异性受体，且PG不参与ANG II诱导的家禽主动脉血管舒张。
