Microvessel O2 Responses in Salt-Sensitive Hypertension

描述(申请人提供)：局部血流控制机制的改变可能在容量扩张型高血压患者从心输出量升高到血管阻力持续升高的转变中发挥重要作用。在许多形式的高血压中，已经证实了随着氧气的增加，小动脉收缩的增强，但对于介导氧气引起的微血管收缩的机制还知之甚少。细胞色素P450(CyP450)4A omega-羟基酶催化20-HETE(花生四烯酸的血管收缩代谢物)的形成，可能是微循环中的02感受器。本研究在盐敏感型高血压遗传模型S大鼠和将正常血压的棕色挪威大鼠的13号染色体替换为S大鼠的遗传背景的SS.BN13大鼠微循环中，研究了细胞色素P450 4504A omega-羟基酶和20-羟乙基乙酸乙酯在介导O2引起的微循环微循环中的作用。SS.BN13雌性大鼠在遗传上与达尔S大鼠有98%的相似性，但不会因高盐饮食而表现出血压升高。有待检验的总体假设是，Dahl S高血压大鼠小动脉对PO2升高的反应增强是由于三个因素中的一个或三个因素的组合：20-HETE产生增加，小动脉对20-HETE的血管收缩作用更敏感，和/或细胞色素P450 4A omega-羟基酶的表达改变。在高盐(HS)和低盐(LS)饮食条件下，20-HETE抑制对在体提睾肌中PO2升高的微动脉反应的影响将在Dahl S和SS.BN13大鼠中被确定。用RT-PCR法和免疫印迹法检测高盐饮食和低盐饮食的S大鼠和BN13大鼠小动脉和实质细胞中细胞色素P450-4A omega-羟基酶亚型的变化，以及小动脉和实质细胞中20-HETE产量随PO2升高的变化。此外，还将比较高盐饮食和低盐饮食不同时间段Dahl S大鼠和SS.BN13大鼠在体微循环中对外源性20-HETE的反应。这些研究应该提供一个更好的理解，在O2供应变化期间，调节血管张力的机制如何在高血压期间和在饮食盐摄入量增加期间改变。

DESCRIPTION (provided by applicant): Alterations in local blood flow control mechanisms may play a major role in the transition from an elevated cardiac output to a maintained elevation in vascular resistance in volume-expanded forms of hypertension. An enhanced constriction of arterioles, in response to increased O2, availability has been demonstrated in many forms of hypertension, but little is known regarding the mechanisms that mediate O2-induced constriction of microvessels. Cytochrome P450 (CYP450) 4A omega-hydroxylase, which catalyzes the formation of 20-HETE (a vasoconstrictor metabolite of arachidonic acid), may act as an 02 sensor in the microcirculation. This study investigates the role of CYP450 4A omega-hydroxylase and 20-HETE in mediating O2-induced constriction of arterioles in the microcirculation of the Dahl S rat, a genetic model of salt sensitive hypertension, and in SS.BN13 consomic rats, in which chromosome 13 of the normotensive Brown Norway rat is substituted into the Dahl S genetic background. The SS.BN13 consomic rats are 98% identical to the Dahl S rat genetically, but do not exhibit elevated blood pressure in response to high salt diet. The overall hypothesis to be tested is that the enhanced response of arterioles to elevated PO2 in Dahl S hypertensive rats is due to one or a combination of 3 factors: increased 20-HETE production, increased sensitivity of arterioles to the vasoconstrictor effects of 20-HETE, and/or altered expression of CYP450 4A omega-hydroxylase. The effect of 20-HETE inhibition, on arteriolar responses to elevated PO2 will be determined in the in situ cremaster muscle of Dahl S and SS.BN13 rats on high salt (HS) and low salt (LS) diets. Cytochrome P450-4A omega-hydroxylase isoforms in arterioles and parenchymal cells of Dahl S rats and SS.BN13 rats on high and low salt diets will be assessed by RT-PCR and Western blotting, and changes in 20-HETE production in response to elevated PO2 will be measured in arterioles and parenchymal cells. Arteriolar constriction in response to exogenous 20-HETE will also be compared in the in situ microcirculation of Dahl S rats and SS.BN13 rats on high salt and low salt diets for various periods of time. These studies should provide an increased understanding of how the mechanisms that regulate vascular tone during changes in 02 availability, are altered during hypertension and during increases in dietary salt intake