Krebs L T, Kramár E A, Hanesworth J M, Sardinia M F, Ball A E, Wright J W, Harding J W
Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman 99164-6520, USA.
Regul Pept. 1996 Dec 3;67(2):123-30. doi: 10.1016/s0167-0115(96)00121-8.
Divalinal-Ang IV [V psi (CH2-NH2)YV psi (CH2-NH2)HPF] is being employed increasingly as a specific AT4 antagonist. This use, which necessitates a comprehensive physiological and pharmacological evaluation of Divalinal-Ang IV's functional and receptor binding characteristics in order to ensure its efficacy and specificity, was the stimulus for this study using bovine adrenal membranes. [125I]Ang IV and [125I]Divalinal-Ang IV were shown to bind with high affinity to a similar number of binding sites, suggesting that both bound the same receptor. This notion was verified by competition curves using [125I]Ang IV and [125I]Divalinal-Ang IV that indicated identical rank order affinities for several angiotensin-related peptides and 100% cross-displacement by Ang IV and Divalinal-Ang IV. Furthermore, an autoradiographic comparison of [125I]Ang IV and [125I]Divalinal-Ang IV in 20 microns sections of bovine adrenals revealed near identical binding distributions characterized by heavy binding in the glomerulosa layer and the medulla. Physiological studies in which test compounds were injected into the internal carotid of the rat and cerebral blood flor (CBF) was measured by laser Doppler flowmetry indicated that pretreatment with Divalinal-Ang IV, but not DuP 753 or PD123177, blocked the increased flow observed with Ang IV infusion. Conversely, DuP 753, but not Divalinal-Ang IV or PD123177, inhibited the decrease in flow witnessed with Ang II. Metabolic stability studies utilizing rat kidney homogenates as a peptidase source, demonstrated that the structural changes present in Divalinal-Ang IV greatly increased its resistance to metabolism as compared to Ang IV. Together, these studies show that Divalinal-Ang IV is a stable, efficacious and specific inhibitor of AT4 receptors.
二缬氨酰 - 血管紧张素IV [V psi (CH2 - NH2)YV psi (CH2 - NH2)HPF] 正越来越多地被用作一种特异性AT4拮抗剂。这种用途需要对二缬氨酰 - 血管紧张素IV的功能和受体结合特性进行全面的生理和药理学评估，以确保其有效性和特异性，这也是本研究使用牛肾上腺膜的动因。[125I]血管紧张素IV和[125I]二缬氨酰 - 血管紧张素IV被证明以高亲和力结合到数量相似的结合位点，这表明两者结合的是同一受体。使用[125I]血管紧张素IV和[125I]二缬氨酰 - 血管紧张素IV的竞争曲线验证了这一概念，该曲线表明几种血管紧张素相关肽具有相同的亲和力排序，并且血管紧张素IV和二缬氨酰 - 血管紧张素IV可实现100%交叉置换。此外，在牛肾上腺20微米切片上对[125I]血管紧张素IV和[125I]二缬氨酰 - 血管紧张素IV进行的放射自显影比较显示，两者的结合分布几乎相同，其特征是在球状带层和髓质中有大量结合。在生理研究中，将测试化合物注入大鼠颈内动脉并通过激光多普勒血流仪测量脑血流量（CBF），结果表明用二缬氨酰 - 血管紧张素IV预处理可阻断血管紧张素IV输注时观察到的血流量增加，但DuP 753或PD123177预处理则无此作用。相反，DuP 753可抑制血管紧张素II引起的血流量减少，而二缬氨酰 - 血管紧张素IV或PD123177则无此作用。利用大鼠肾脏匀浆作为肽酶来源的代谢稳定性研究表明，与血管紧张素IV相比，二缬氨酰 - 血管紧张素IV中的结构变化极大地增加了其对代谢的抗性。这些研究共同表明，二缬氨酰 - 血管紧张素IV是一种稳定、有效且特异性的AT4受体抑制剂。
