Regulation of Adrenal Vascular Tone by Steroidogenic Cells

描述(申请人提供)：血管紧张素II(AII)是一种血管收缩药，可刺激肾上腺皮质的肾小球带(ZG)细胞释放醛固酮。醛固酮调节钠、钾平衡和血压。肾上腺血流量(ABF)对醛固酮的合成和作用都是至关重要的。ABF向ZG细胞输送氧气、营养素、胆固醇酯和AII，并将醛固酮输送到其目标组织。因此，影响肾上腺血管张力的机制对ABF的调节和类固醇的生成是重要的。AII及其代谢物对肾上腺血管张力和类固醇生成的肾上腺内调节作用知之甚少。长期目标是了解肾上腺内血管张力、ABF和类固醇合成的调节，以及ABF和类固醇合成的偶联。ZG细胞在解剖上非常接近肾上腺皮质内的肾上腺小动脉，允许相互作用。我们已经确定了ZG细胞通过释放环氧二十碳三烯酸(EETs)来调节肾上腺血管张力的新机制，EETs导致血管松弛。在PM浓度下，AII通过两种机制松弛肾上腺动脉。AII通过血管内皮细胞释放一氧化氮(NO)，间接通过ZG细胞释放EETs，对肾上腺动脉起到松弛作用。这些发现表明ZG细胞在调节肾上腺血管张力和类固醇生成方面起着中心作用。ZG细胞代谢AII的主要途径是氨基肽酶A(APA)将其转化为血管紧张素III(AIII)。AIII在肾上腺皮质中有一个新的作用。在刺激ZG细胞依赖的EET介导的松弛方面，AIII的效力是AII的10倍。抑制AII对AIII的代谢，阻断ZG细胞介导的对AII的松弛。因此，AII对AIII的代谢对AII调节肾上腺血管张力和ABF至关重要。我们在这个方案中的目的是了解ZG细胞的AII代谢在调节肾上腺血管张力、ABF和醛固酮释放方面的重要性。中心假说是APA对AIII的代谢是ZG细胞介导的血管松弛的必经步骤，AII增加ABF。这表明APA在调节肾上腺血管张力和ABF中起重要作用。核心假说将通过三个目标进行检验。(1)我们将通过分离的ZG细胞确定AII代谢的途径，以及AII代谢对EET和醛固酮释放的影响。我们的假设是，ZG细胞将AII代谢成AIII，从而调节EET的AII刺激，但不调节醛固酮的释放。(2)明确AII调节肾上腺皮质动脉张力的机制。我们的假设是，对AIII和APA活性的所有代谢对ZG细胞依赖的EET介导的血管松弛至关重要。(3)在麻醉大鼠体内，建立AII代谢和ZG细胞来源的EET在ABF调节中的作用。我们的假设是，APA对AIII的所有代谢是ABF中AII增加所必需的。这些研究将表明，AII到AIII的代谢是否是ZG细胞调节肾上腺血管张力和ABF的必需步骤。APA可能决定ZG细胞介导的EET和/或内皮介导的NO机制是否对抗AII的收缩，并将ABF维持在高肾素状态。

DESCRIPTION (provided by applicant): Angiotensin II (AII), a vasoconstrictor, stimulates aldosterone release from the zona glomerulosa (ZG) cells of the adrenal cortex. Aldosterone regulates sodium and potassium balance and blood pressure. Adrenal blood flow (ABF) is critical to both aldosterone synthesis and action. ABF delivers oxygen, nutrients, cholesterol esters and AII to ZG cells and carries aldosterone to its target tissues. Thus, mechanisms that influence adrenal vascular tone are important to ABF regulation and steroidogenesis. The intra-adrenal regulation of adrenal vascular tone and steroidogenesis by AII and its metabolites is poorly understood. The long-term goal is to understand the intraadrenal regulation of vascular tone, ABF and steroidogenesis and the coupling of ABF and steroidogenesis. ZG cells are in close anatomical proximity to the adrenal arterioles in the adrenal cortex allowing interactions. We have defined the novel mechanism that ZG cells regulate adrenal vascular tone by releasing epoxyeicosatrienoic acids (EETs) that cause vasorelaxation. In pM concentrations, AII relaxes adrenal arteries by two mechanisms. AII relaxes adrenal arteries directly by endothelial release of nitric oxide (NO) and indirectly by ZG cell release of EETs. These findings indicate the central role of ZG cells in regulating both adrenal vascular tone and steroidogenesis. The major ZG cell pathway for AII metabolism is its conversion to angiotensin III (AIII) by aminopeptidase A (APA). AIII has a new role in the adrenal cortex. AIII is 10-fold more potent than AII in stimulating ZG cell-dependent, EET-mediated relaxation. Inhibition of AII metabolism to AIII blocks the ZG cell-mediated relaxation to AII. Thus, AII metabolism to AIII is critical for the regulation of adrenal vascular tone and ABF by AII. Our objective in this proposal is to understand the importance of AII metabolism by ZG cells in regulating adrenal vascular tone, ABF and aldosterone release. The central hypothesis is that AII metabolism to AIII by APA is an obligatory step for ZG cell-mediated vasorelaxation and increases in ABF by AII. This indicates an important role for APA in regulating adrenal vascular tone and ABF. The central hypothesis will be tested with three aims. (1) We will identify the pathways of AII metabolism by isolated ZG cells and the impact of AII metabolism on EET and aldosterone release. Our hypothesis is that ZG cells metabolize AII to AIII and thereby regulate AII stimulation of EET, but not aldosterone, release. (2) We will identify the mechanisms by which AII regulates vascular tone in isolated adrenal cortical arteries. Our hypothesis is that AII metabolism to AIII and APA activity are critical for ZG cell-dependent, EET-mediated vasorelaxation. (3) We will establish the role of AII metabolism and ZG cell-derived EETs in the regulation of ABF in vivo in anesthetized rats. Our hypothesis is that AII metabolism to AIII by APA is essential for AII increases in ABF. These studies will indicate if metabolism of AII to AIII is an obligatory step to the regulation of adrenal vascular tone and ABF by ZG cells. APA may determine whether ZG cell-mediated EET- and/or endothelial-mediated NO mechanisms oppose the constriction by AII and maintain ABF in high renin states.